hsc 3110 ch.13

components of an active lifestyle

COMPONENTS OF AN ACTIVE LIFESTYLE Despite the many benefits of an active lifestyle, levels of physical activity remain low for all populations of Americans. In 2016, the Centers for Disease Control and Prevention (CDC) reported the following statistics about the proportion of adult Americans who meet the CDC recommendations for aerobic and muscle-strengthening exercise: Only 20.6% of U.S. adults met both aerobic and muscle-strengthening guidelines, but compliance by state varied from 12.7% (West Virginia) to 26.7% (Colorado). Check to see how your state compares at the website for CDC's Nutrition, Physical Activity, and Obesity: Data, Trends, and Maps (https://nccd.cdc.gov/NPAO_DTM). Nearly 52% of adults met the aerobics recommendation, but only 29% met the muscle-strengthening guidelines. People with higher levels of education were more active than people with lower educational attainment, younger people were more active than older people, and men were more active than women.Page 350 Other studies found that 12% of Americans report exercising vigorously for more than 20 minutes, three times per week. However, electronic measurements of people involved in normal daily activity showed that the actual proportion is closer to 3%. Most surveys show large gaps in exercise habits of Americans based on ethnicity, socioeconomic status, and education level. Regardless of statistics, however, evidence is growing that becoming more physically active may be the single most important lifestyle change for promoting health and well-being. QUICK STATS Fewer than 3 in 10 high school students get at least 60 minutes of physical activity every day. —Centers for Disease Control and Prevention, 2016 Levels of Physical Activity Physical activity is any body movement carried out by the skeletal muscles that requires energy. Different types of physical activity can be arranged on a continuum based on the amount of energy they require. Quick, easy movements such as standing up or walking down a hallway require little energy or effort. More intense, sustained activities such as cycling five miles or running in a race require considerably more. Exercise refers to a subset of physical activity—planned, structured, repetitive movement of the body intended specifically to improve or maintain physical fitness. To develop fitness, a person must perform enough physical activity to stress the body and cause long-term physiological changes. Moderate-intensity physical activity is essential to health and confers wide-ranging health benefits, but more intense exercise is necessary to improve physical fitness. This important distinction between physical activity and exercise is a key concept in understanding the guidelines discussed in this chapter. Ask Yourself QUESTIONS FOR CRITICAL THINKING AND REFLECTION When you think about exercise, do you think of only one or two of the five components of health-related fitness, such as muscular strength or body composition? If so, where do you think your ideas come from? What role do the media play in shaping your ideas about fitness? Increasing Physical Activity In 2011, the American College of Sports Medicine (ACSM) released the newest version of its exercise guidelines for healthy adults. This update followed the 2010 U.S. Surgeon General's report on overweight and obesity in American children and adults, The Surgeon General's Vision for a Healthy and Fit Nation, and the landmark 2008 report from the U.S. Department of Health and Human Services, Physical Activity Guidelines for Americans. Although each of these reports has a somewhat different focus, they all stress the importance of regular physical activity for health, wellness, and the prevention of chronic diseases and premature death. The 2011 guidelines include the following key recommendations for adults: For substantial health benefits, adults should do at least 150 minutes (2.5 hours) a week of moderate-intensity aerobic physical activity, or 75 minutes (1 hour and 15 minutes) a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity. Activity should preferably be spread throughout the week. For additional and more extensive health benefits, adults should increase their aerobic physical activity to 300 minutes (5 hours) a week of moderate-intensity activity, or 150 minutes (2.5 hours) a week of vigorous-intensity activity, or an equivalent combination of moderate- and vigorous-intensity activity. Adults can enjoy additional health benefits by engaging in physical activity beyond this amount. Adults should also do muscle-strengthening activities that are moderate or high intensity and involve all major muscle groups on two or more days a week; these activities provide additional health benefits. Everyone should avoid inactivity. Adults, teenagers, and children should spend less time in front of a television or computer screen because it decreases metabolic health and contributes to a sedentary lifestyle and increases the risk of obesity. The reports state that physical activity benefits people of all ages and of all racial and ethnic groups, including people with disabilities. The benefits of activity outweigh the dangers. Page 351 These levels of physical activity promote health and wellness by lowering the risk of high blood pressure, stroke, heart disease, type 2 diabetes, colon cancer, and osteoporosis and by reducing feelings of mild to moderate depression and anxiety. What's the difference between moderate- and vigorous-intensity physical activity? 2008 Physical Activity Guidelines for Americans defines moderate-intensity physical activity as activity that causes a noticeable increase in heart rate, such as brisk walking. Vigorous-intensity physical activity is activity that causes rapid breathing and a substantial increase in heart rate, such as jogging. Figure 13.4 shows examples of moderate activities. Brisk walking, dancing, swimming, cycling, and yardwork can all help you meet the physical activity recommendations. You can burn the same number of calories by doing a moderate-intensity activity for a longer time or higher-intensity activity for a shorter time. For more examples of moderate and vigorous activities, see Table 13.1. Table 13.2 summarizes the physical activity recommendations for promoting general health, fitness, and weight management. Activities listed from least to most vigorous. The less vigorous, the more time needed to burn 150 calories; the more vigorous, the less time needed. [D] FIGURE 13.4 Examples of moderate amounts of physical activity. note: Each example uses about 150 calories. source: National Heart, Lung, and Blood Institute. 2010. Why Is Exercise Important? (http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/phy_act.htm). Table 13.1 Examples of Moderate- and Vigorous-Intensity Exercise MODERATE-INTENSITY PHYSICAL ACTIVITY (requires a moderate amount of effort and noticeably accelerates the heart rate) VIGOROUS-INTENSITY PHYSICAL ACTIVITY (requires a large amount of effort and causes rapid breathing and a substantial increase in heart rate) Brisk walking Walking/climbing briskly up a hill Dancing Running Gardening Fast cycling Housework and domestic chores Aerobics Doubles tennis Fast swimming Active involvement in games and sports with children/walking domestic animals Competitive sports and games (e.g., traditional games, singles tennis, football, volleyball, hockey, basketball) General building tasks (e.g., roofing, thatching, painting) Heavy shoveling or digging ditches Carrying/moving moderate loads (less than 45 pounds) Carrying/moving heavy loads (greater than 45 pounds) source: Reprinted with permission from WHO from Global Strategy on Diet, Physical Activity and Health, What is Moderate-intensity and Vigorous-intensity Physical Activity? Table 13.2 Physical Activity and Exercise Recommendations for Promoting General Health, Fitness, and Weight Management GOAL RECOMMENDATION General health Perform moderate-intensity aerobic physical activity for at least 150 minutes per week or 75 minutes of vigorous-intensity physical activity per week. Also, be more active in your daily life: Walk instead of driving, take the stairs instead of the elevator, and watch less television. Increased health and fitness benefits Exercise at a moderate intensity for 300 minutes per week or at a vigorous intensity for 150 minutes per week. Achieve or maintain weight loss Exercise at a moderate intensity for 60-90 minutes per day on most days of the week. Muscle strength and endurance Perform one or more sets of resistance exercises that work the major muscle groups for 8-12 repetitions (10-15 reps with a lighter weight for older adults) on 2 or 3 nonconsecutive days per week. Examples include weight training and exercises that use body weight as resistance (such as core-stabilizing exercises, pull-ups, push-ups, lunges, and squats). Flexibility Perform range-of-motion (stretching) exercises at least 2 days per week. Hold each stretch for 10-30 seconds. Neuromuscular training Older people should do balance training 2 or 3 days per week. Examples include yoga, tai chi, and balance exercises (standing on one foot, step-ups, and walking lunges). These exercises are also beneficial for young and middle-aged adults. sources: Garber, C. E., et al. 2011. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: Guidance for prescribing exercise. Medicine & Science in Sports & Exercise 43(7): 1334-1359; American Heart Association. 2015. American Heart Association Recommendations for Physical Activity in Adults (http://www.heart.org). The daily total of physical activity can be accumulated in multiple bouts of 10 or more minutes—for example, two 10-minute bike rides to and from class and a brisk 10-minute walk to the store. In this lifestyle approach to physical activity, people can choose activities that they find enjoyable and that fit into their daily routine. Everyday tasks at school, work, and home can be structured to contribute to the daily activity total (see the box "Making Time for Physical Activity"). If all Americans who are currently sedentary were to increase their lifestyle physical activity to 150 minutes per week, the benefit to public health and individual well-being would be enormous. TAKE CHARGE: Making Time for Physical Activity "Too little time" is a common excuse for not being physically active. Learning to manage your time successfully is crucial if you are to maintain a wellness lifestyle. Begin by keeping a record of how you currently spend your time. List each type of activity and the total time you engaged in it on a given day—for example, sleeping, 7 hours; eating, 1.5 hours; studying, 3 hours; and so on. Prioritize your activities according to how important they are to you, from essential to somewhat important to not important at all. Make changes in your daily schedule by subtracting time from some activities in order to make time for physical activity. Look carefully at your leisure-time activities and your methods of transportation—these are areas where it is easy to build in physical activity. For example, you may choose to reduce the total amount of time you spend playing computer games to make time for an after-dinner bike ride or a walk with a friend. You may decide to watch 10 fewer minutes of television in the morning to change your 5-minute drive to class into a 15-minute walk. Here are just a few ways to incorporate more physical activity into your daily routine: Take the stairs instead of the elevator or escalator. Walk to the mailbox, post office, store, bank, or library whenever possible. Do at least one chore every day that requires physical activity: Wash the windows or your car, clean your room or house, mow the lawn, or rake the leaves. Take study or work breaks to avoid sitting for more than 30 minutes at a time. Get up and walk around the library, your office, or your home or dorm; go up and down a flight of stairs. When you take public transportation, get off one stop early and walk to your destination. Take the dog for a walk every day. If weather or neighborhood safety rule out walking outside, look for alternative locations—an indoor track, an enclosed shopping mall, or even a long hallway. Seize every opportunity to get up and walk around. Move more and sit less. Increasing Physical Activity to Manage Weight Because more than two-thirds of Americans are overweight, the U.S. Department of Health and Human Services also published physical activity guidelines focusing on weight management. These guidelines recognize that for people who need to prevent weight gain, lose weight, or maintain weight loss, 150 minutes per week of physical activity may not be enough. Instead they recommend up to 90 minutes of physical activity per day. Exercising to Improve Physical Fitness As mentioned earlier, moderate-intensity physical activity confers significant health and wellness benefits, especially for those who are currently sedentary and become moderately active. However, people can obtain even greater health and wellness benefits by increasing the duration and intensity of physical activity. With increased activity, they will see more improvements in quality of life and greater reductions in disease and mortality risk. More vigorous activity—as in a structured, systematic exercise program—is also needed to improve physical fitness; moderate physical activity alone is not enough. Physical fitness requires more intense movement that poses a substantially greater challenge to the body. Reducing Sedentary Time Researchers have found that too much sedentary time—sitting too much—is detrimental to health regardless of Page 352whether an individual meets the physical activity goals for health or exercise. A 2015 review found that sedentary time was associated with increased risk of disease and death independent of activity level. The risk of negative outcomes from sedentary time was lower among people with higher levels of physical activity, but they were not eliminated. How does sedentary time affect health? Although not completely understood, sedentary time is associated with markers of poor metabolic functioning, including unhealthy levels of blood glucose, insulin, and blood fats, as well as a large waist circumference. A study that looked at the impact of increased sedentary time in moderately active individuals found that sitting for more than 30 or 60 minutes at a time Page 353resulted in significantly elevated glucose and insulin levels. Sedentary time also affects blood fats and markers for inflammation. All these factors can contribute to the development of type 2 diabetes, metabolic syndrome, heart disease, and cancer. What does this mean for an individual? Studies have found that the average American adult spends more than half her or his waking day in sedentary activities, such as using a computer, studying, or watching television. Luckily, evidence so far suggests that frequent breaks from sedentary time—2 minutes every 20 or 30 minutes, for example—protect against some impacts of sedentary time. So, take frequent breaks when you are engaged in sedentary activities, whether at work or school or during leisure time. Try the strategies suggested in the box "Move More, Sit Less" and invent your own. TAKE CHARGE: Move More, Sit Less Regular exercise provides huge wellness benefits, but it does not cancel out all the negative effects of too much sitting during the day. Advances in technology promote sedentary behavior: We can now work or study at a desk, watch TV or play video games in our leisure time, order take-out and delivery for meals, and shop and bank online. To avoid the negative health effects of too little daily activity, try some of the following strategies: Stand up and/or walk when you are at work or making personal phone calls. Take the stairs whenever and wherever you can; walk up and down escalators instead of riding them. At work, walk to a coworker's desk rather than e-mailing or calling, take the long route to the restroom, and take a walk break whenever you take a coffee or snack break. Drink plenty of water so that you'll have to take frequent restroom breaks. Set reminders to get up and move: Use commercial breaks while watching TV to remind yourself to move or stretch. At work or while using a digital device, set the clock function on your computer or phone to remind you to get up at least every hour. Moving every 20 or 30 minutes is even better. Engage in active chores and leisure activities. Track your sedentary time to get a baseline, and then continue monitoring to note any improvements. You can also use a step counter to track your general activity level and movement patterns. Ask Yourself QUESTIONS FOR CRITICAL THINKING AND REFLECTION Does your current lifestyle include enough physical activity—150 minutes of moderate-intensity activity a week—to support health and wellness? Do you go beyond this level to include enough vigorous activity and exercise to build physical fitness? What changes could you make in your lifestyle to start developing physical fitness?

what is physical fitness

WHAT IS PHYSICAL FITNESS? Physical fitness is a set of physical attributes that allow the body to respond or adapt to the demands and stress of physical effort—to perform moderate to vigorous levels of physical activity without becoming overly tired. A person's level of fitness depends on physiological factors, such as the heart's ability to pump blood and the energy-generating capacity of the cells. These factors depend on genetics—a person's inborn potential for physical fitness—and on behavior—getting enough physical activity to stress the body and cause long-term physiological changes. Some components of fitness are related to specific activities or sports, whereas others relate to general health. Health-related fitness includes the following components: Cardiorespiratory endurance Muscular strengthPage 348 Muscular endurance Flexibility Body composition Health-related fitness helps you withstand physical challenges and protects you from diseases. Cardiorespiratory Endurance Cardiorespiratory endurance is the ability to perform prolonged, large-muscle, dynamic exercise at moderate to high intensity. It depends on factors such as the lungs' ability to deliver oxygen to the bloodstream, the heart's capacity to pump blood, the ability of the nervous system and blood vessels to regulate blood flow, and the cells' ability to use oxygen and process fuels for exercise. When cardiorespiratory fitness is low, the heart has to work hard during normal daily activities and may not be able to work hard enough to sustain high-intensity physical activity in an emergency. Poor cardiorespiratory fitness is linked with heart disease, diabetes, colon cancer, stroke, depression, anxiety, and premature death from all causes. Regular cardiorespiratory endurance training, however, conditions the heart and metabolism. Endurance training makes the heart stronger and improves the function of the entire cardiorespiratory system. As cardiorespiratory fitness improves, related physical functions also improve: The heart pumps more blood per heartbeat. Resting heart rate slows and resting blood pressure decreases. Blood volume increases. Blood supply to tissues improves. The body can cool itself better. Metabolic health improves, which helps the body process fuels and regulate cell function. A healthy heart can better withstand the strains of daily life, the stress of occasional emergencies, and the wear and tear of time. Endurance training also improves the function of the body's chemical systems, particularly in the muscles and liver, enhancing the body's ability to use energy from food and to do more exercise with less effort. You can develop cardiorespiratory endurance through activities that involve continuous, rhythmic movements of large muscle groups, such as the legs. Such activities include walking, jogging, cycling, and aerobic dancing. Muscular Strength Muscular strength is the amount of force a muscle can produce with a single maximum effort. It depends on factors such as the size of muscle cells and the ability of nerves to activate muscle cells. Strong muscles are important for everyday activities, such as climbing stairs, as well as for emergencies. Strong muscles help keep the skeleton in proper alignment, preventing back and leg pain and providing the support necessary for good posture. Recreational activities also require muscular strength: Strong people can hit a tennis ball harder, kick a soccer ball farther, and ride a bicycle uphill more easily. Cardiorespiratory endurance is a critical component of fitness. © Blend Images/Michael DeYoung/Getty Images RF Muscle tissue is an important element of overall body composition. Greater muscle mass makes possible a higher rate of metabolism and faster energy use, which help people to maintain a healthy body weight. Maintaining strength and muscle mass is vital for healthy aging. Older people tend to lose muscle cells (a condition called sarcopenia), and many of the remaining muscle cells become nonfunctional because they lose their attachment to the nervous system. Strength training helps maintain muscle mass, function, and balance in older people, which greatly enhances their quality of life and prevents injuries. Strength training promotes cardiovascular health, reduces the risk of osteoporosis (bone loss), and prevents premature death from all causes. Page 349 Muscular strength can be developed by training with weights or by using the weight of the body for resistance during calisthenic exercises such as push-ups and curl-ups. Muscular Endurance Muscular endurance is the ability to resist fatigue and sustain a given level of muscle tension—that is, to hold a muscle contraction for a long time or to contract a muscle over and over again. It depends on factors such as the size of muscle cells, the ability of muscles to store fuel, the content of mitochondria (cell energy centers), and the blood supply to muscles. Muscular endurance is important for good posture and for injury prevention. For example, if abdominal and back muscles cannot hold the spine correctly, the chances of low-back pain and back injury are increased. In fact, good muscular endurance in the trunk muscles is more important than muscular strength for preventing back pain. Muscular endurance helps people cope with the physical demands of everyday life and enhances performance in sports and work. Stressing the muscles with a greater load (weight) than they are accustomed to develops muscle endurance as well as muscular strength. The degree to which strength or endurance develops depends on the type and amount of stress that is applied. Flexibility Flexibility is the ability of joints to move through their full range of motion. It depends on joint structure, the length and elasticity of connective tissue, and nervous system activity. Flexible, pain-free joints are important for good health and well-being. Inactivity causes the joints to become stiffer with age. Stiffness, in turn, often causes older people to assume unnatural body postures that can stress joints and muscles. Stretching exercises can help ensure a healthy range of motion for all major joints. Body Composition As discussed earlier, body composition refers to the proportion of fat and fat-free mass (muscle, bone, and water) in the body. Healthy body composition involves a high proportion of fat-free mass and an acceptably low level of body fat, adjusted for age and sex. The best way to lose fat is through a lifestyle that includes a sensible diet and exercise. The best way to add muscle mass is through resistance training such as weight training. (Chapter 14 discusses body composition in detail.) Skill-Related Components of Fitness In addition to the five health-related components of physical fitness, the ability to perform a particular sport or activity may depend on skill-related fitness components such as the following: Speed. The ability to perform a movement in a short period of time. Power. The ability to exert force rapidly, based on a combination of strength and speed. Agility. The ability to change the body's position quickly and accurately. Balance. The ability to maintain equilibrium while either moving or stationary. Coordination. The ability to perform motor tasks accurately and smoothly using body movements and the senses. Reaction time. The ability to respond quickly to a stimulus. Skill-related fitness is sport specific and is best developed through practice. For example, playing basketball best develops the speed, coordination, and agility needed to play basketball. Playing a sport can be fun, can help build fitness, and may contribute to other areas of wellness.

designing your exercise program

DESIGNING YOUR EXERCISE PROGRAM The best exercise program has two primary characteristics: It promotes your health, and it's fun for you to do. Exercise can provide some of the most pleasurable moments of your day, once you make it a habit. A little thought and planning will help you achieve these goals. Figure 13.5 shows a physical activity pyramid. At the top, the small triangle represents what you should limit: sedentary activities. The wide section at the bottom of the pyramid shows activities that you should engage in more frequently throughout the day: walking, climbing stairs, doing yardwork, and sweeping the floor. From there, work up to meeting the goal of 150 minutes of moderate-intensity exercise per week. Choose to be active whenever you can. If weight management is a concern for you, begin by achieving the goal of 150 minutes per week and then gradually increase your activity level to 300 minutes per week while reducing caloric intake, especially from added sugars and other empty calories (see Chapter 12). Detailed physical activity pyramid guidelines, listed from the base of the pyramid to the top. [D] FIGURE 13.5 Physical activity pyramid. Make activities at the base of the pyramid part of your everyday life; limit the amount of time you spend in the sedentary activities listed at the top. © Stockbyte/PunchStock; © Ryan McVay/Getty Images RF; © McGraw Hill Education/Seth Foley, photographer; © Joaquin Palting/Getty Images RF; © Doug Menuez/Getty Images RF; © UpperCut Images/Alamy For even greater benefits, move up to the next two levels of the pyramid, which illustrate parts of a formal exercise program. They take up less of your time than the activities on the lower two levels of the pyramid, but they will develop all the health-related components of physical fitness. As described earlier, regardless of your pattern of physical activity and formal exercise, you should limit your overall sedentary time (the tip of the pyramid) and take frequent active breaks. New research shows that high-intensity interval training—repetitions of high-intensity exercise followed by rest—builds fitness rapidly in less time than traditional aerobic training (see the box "Interval Training: Pros and Cons"). The remaining sections of this chapter will show you how to develop a personalized exercise program. For a summary of the health and fitness benefits of different levels of physical activity, see Figure 13.6. TAKE CHARGE: Interval Training: Pros and Cons Few exercise techniques are more effective at improving fitness rapidly than high-intensity interval training (HIIT)—a series of very brief, high-intensity exercise sessions interspersed with short rest periods. The four components of interval training are distance, repetition, intensity, and rest, defined as follows: Distance refers to either the distance or the time of the exercise interval. Repetition is the number of times the exercise is repeated. Intensity is the speed at which the exercise is performed. Rest is the time spent recovering between exercises. Canadian researchers found that six sessions of high-intensity interval training (HIIT) on a stationary bike increased muscle oxidative capacity by almost 50%, muscle glycogen by 20%, and cycle endurance capacity by 100%. The subjects made these amazing improvements by exercising only 15 minutes in two weeks. Each workout consisted of 4-7 repetitions of high-intensity exercise (each repetition consisted of 30 seconds at near-maximum effort) on a stationary bike. Follow-up studies showed that practicing HIIT three times per week for six weeks improved endurance and aerobic capacity just as well as training five times per week for 60 minutes for six weeks. These studies (and more than 60 others) showed the value of high-intensity training for building aerobic capacity and endurance. You can use interval training in your favorite aerobic exercises. In fact, the type of exercise you select is not important as long as you exercise at a high intensity. HIIT training can even be used to help develop sports skills. For example, a runner might do 4-7 repetitions of 200-meter sprints at near-maximum effort. A tennis player might practice volleys against a wall as fast as possible for 4-8 repetitions lasting 30 seconds each. A swimmer might swim 4-8 repetitions of 50 meters at 100% effort. It is important to rest 3-5 minutes between repetitions, regardless of the type of exercise being performed. If you add HIIT to your exercise program, do not practice interval training more than 3 days per week. Intervals are exhausting and easily lead to injury. Let your body tell you how many days you can tolerate. If you become overly tired after doing interval training 3 days per week, cut back to 2 days. If you feel good, try increasing the intensity or number of intervals (but not the number of days per week) and see what happens. As with any kind of exercise program, begin HIIT training slowly and progress conservatively. Although the Canadian studies showed that HIIT training produced substantial fitness improvements by themselves, it is best to integrate HIIT into a total exercise program. High-intensity interval training appears to be safe and effective in the short term, but there are concerns about the long-term safety and effectiveness of this type of training, so consider the following issues: Maximal-intensity training could be dangerous for some people. A physician might be reluctant to give certain patients the green light for this type of exercise. Always warm up with several minutes of low-intensity exercise before practicing HIIT. Maximal-intensity exercise without a warm-up can cause cardiac arrhythmias (abnormal heart rhythms) even in healthy people. High-intensity interval training might trigger overuse injuries in unfit people. For this reason, it is essential to start gradually, especially for someone at a low level of fitness. Exercise at submaximal intensities for at least four to six weeks before starting HIIT. Cut back on interval training or rest if you feel overly fatigued or develop overly sore joints or muscles. Chart compares lifestyle physical activity with both moderate and vigorous exercise programs. [D] FIGURE 13.6 Health and fitness benefits of different amounts of physical activity and exercise. © RubberBall Productions; © Royalty-Free/CORBIS; © Thinkstock Images/Jupiter Images RF First Steps Are you thinking about starting a formal exercise program? A little planning can help make it a success.Page 355 Medical Clearance Previously inactive men over 40 and women over 50 should get a medical examination before beginning an exercise program. Diabetes, asthma, heart disease, and extreme obesity are conditions that may call for a modified program. If you have an increased risk of heart disease because of smoking, high blood pressure, or obesity, get a physical checkup, including an electrocardiogram (ECG or EKG), before beginning an exercise program. Basic Principles of Physical Training To put together an effective exercise program, you should first understand the basic principles of physical training. Specificity To develop a fitness component, you must perform exercises that are specifically designed for that component. This is the principle of specificity. Weight training, for example, develops muscular strength but is less effective for developing flexibility or cardiorespiratory endurance. Specificity also applies to the skill-related fitness components and to the different parts of the body. A well-rounded exercise program includes exercises geared to each component of fitness, to different parts of the body, and to specific activities or sports. Progressive Overload Your body adapts to the demands of exercise by improving its functioning. When the amount of exercise, or overload, is increased progressively, Page 356fitness continues to improve. This training principle is called progressive overload. Too little exercise has no effect on fitness; too much may cause injury. The appropriate amount depends on your current level of fitness, your genetic capacity to adapt to exercise, your fitness goals, and the fitness components being developed. The amount of overload needed to maintain or improve a particular level of fitness is determined in four dimensions, represented by the acronym FITT: Frequency Intensity Time Type Frequency, or how often. Optimal exercise frequency, expressed in number of days per week, varies with the component being developed, how vigorously you exercise, and your goals. A frequency of 3-5 days per week is recommended for cardiorespiratory endurance exercise, 2 or 3 days per week for strength training, and 2 or 3 days per week (ideally 5-7 days per week) for stretching. Intensity, or how hard. Fitness benefits occur when you exercise harder than your usual level of activity. To develop cardiorespiratory endurance, you must raise your heart rate above normal; to develop muscular strength, you must lift a heavier weight than you normally do; to develop flexibility, you must stretch your muscles beyond their usual length. A gradual increase in intensity is recommended to avoid injury. Time (duration), or how long. If fitness benefits are to occur, exercise sessions must last for an extended period. Depending on the component being developed and your intensity level, a duration 20-60 minutes is usually recommended. The U.S. Department of Health and Human Services exercise recommendations are to accumulate at least 150 minutes per week of moderate-intensity physical activity. Type, or mode of activity. The type of exercise in which you should engage varies with each fitness component and with your personal fitness goals. To develop cardiorespiratory endurance, you need to engage in continuous activities involving large muscle groups—walking, cycling, or swimming, for example. Resistance exercises develop muscular strength and endurance; stretching exercises build flexibility. The frequency, intensity, and time of exercise will be different for each type of activity. Rest and Recuperation Fitness gains occur following exercise as the body adapts to the stress of training. Adequate rest is as important to this process as training. Overtraining—an imbalance between training and recovery—leads to injury, illness, and excessive fatigue. Reversibility The body adjusts to lower levels of physical activity the same way it adjusts to higher levels—this is the principle of reversibility. When you stop exercising, you can lose up to 50% of fitness improvements within two months. Try to exercise consistently, and don't quit if you miss a few workouts. If you must temporarily curtail your training, you can maintain your fitness improvements by keeping the intensity of your workouts constant while reducing their frequency or duration. Individual Differences There are genetic limits to how much a person can improve fitness, as well as large individual differences between people in their ability to improve fitness, achieve a desirable body composition, and perform and learn sports skills. In studies, some people on a diet and exercise program improve fitness by 50%, whereas others on the same program improve by only 2-3%. It is more difficult for those whose bodies don't respond as well to exercise to make changes in fitness or body fat levels. Elite athletes start out with a genetic advantage over the average person. However, everyone has the capacity to improve fitness and reap the health benefits of exercise. Selecting Activities If you have been inactive, begin by gradually increasing the amount of moderate physical activity in your life (the bottom of the activity pyramid shown in Figure 13.5). Once your body adjusts to your new level of activity, you can choose additional activities for your exercise program. Be sure the activities you choose contribute to your overall wellness and make sense for you. Are you competitive? If so, try racquetball, basketball, or squash. Do you prefer to exercise alone? Then consider cross-country skiing or road running. Have you been sedentary? A walking program may be a good place to start. If you think you may have trouble sticking with an exercise program, find a structured activity that you can do with a friend, a personal trainer, or a group. Be realistic about the constraints presented by some sports, such as accessibility, expense, and time. For example, if you have to travel for hours to get to a ski area, skiing may not be a good choice for your regular exercise program. And if you've never played tennis, it will probably take some time to reach a reasonable skill level; you may be better off with a program of walking or jogging to get good workouts as you're improving your tennis game. Ask Yourself QUESTIONS FOR CRITICAL THINKING AND REFLECTION Which benefits of exercise are most important to you, and why? For example, is there a history of heart disease or diabetes in your family? Have you thought about how regular exercise could reduce your risks for specific diseases? Page 357 Cardiorespiratory Endurance Exercise Exercises that condition your heart and lungs and improve your metabolism should have a central role in your fitness program. Frequency The optimal workout schedule for endurance training is 3-5 days per week. Beginners should start with 3 days and work up to 5 days. Training more than 5 days a week often leads to injury for recreational athletes. Although you get health benefits from exercising vigorously only 1 or 2 days per week, you risk injury because your body never gets a chance to adapt fully to regular exercise training. Intensity The most misunderstood aspect of conditioning, even among experienced athletes, is training intensity. Intensity is the crucial factor in attaining a significant training effect—that is, in increasing the body's cardiorespiratory capacity. A primary purpose of endurance training is to increase maximal oxygen consumption (V.O2max). V.O2max represents the cells' maximum ability to use oxygen and is considered the best measure of cardiorespiratory capacity. Intensity of training is the crucial factor in improving V.O2max. One of the easiest ways to determine exactly how intensely you should work involves measuring your heart rate. It is not necessary or desirable to exercise at your maximum heart rate—the fastest heart rate possible before exhaustion sets in—to improve your cardiorespiratory capacity. Beneficial effects occur at lower heart rates with a much lower risk of injury. Your target heart rate zone is the range of rates within which you should exercise to obtain cardiorespiratory benefits. To determine the intensity at which you should exercise, see the box "Determine Your Target Heart Rate" and Figure 13.7. TAKE CHARGE: Determine Your Target Heart Rate One of the best ways to monitor the intensity of cardiorespiratory endurance exercise is to measure your heart rate. It isn't necessary to exercise at your maximum heart rate to improve maximal oxygen consumption. Fitness adaptations occur at lower heart rates with a much lower risk of injury. According to the American College of Sports Medicine, your target heart rate zone—rates at which you should exercise to experience cardiorespiratory benefits—is between 65% and 90% of your maximum heart rate. To calculate your target heart rate zone, follow these steps: Estimate your maximum heart rate (MHR) by subtracting your age from 220, or have it measured precisely by undergoing an exercise stress test in a doctor's office, hospital, or sports medicine lab. (Note: The formula to estimate MHR carries an error of about ±10-15 beats per minute [bpm] and can be very inaccurate for some people, particularly older adults and young children.) Multiply your MHR by 65% and 90% to calculate your target heart rate zone. Very unfit people should use 55% of MHR for their training threshold. For example, a 19-year-old would calculate her target heart rate zone as follows: MHR = 220 − 19 = 201 65% training intensity = 0.65 × 201 = 131 bpm 90% training intensity = 0.90 × 201 = 181 bpm To gain fitness benefits, the young woman in our example would have to exercise at an intensity that raises her heart rate to between 131 and 181 bpm. An alternative method for calculating target heart rate range uses heart rate reserve, the difference between maximum heart rate and resting heart rate. With this method, target heart rate is equal to resting heart rate plus between 50% (40% for very unfit people) and 85% of heart rate reserve. Although some people (particularly those with very low levels of fitness) will obtain more accurate results using this more complex method, both methods provide reasonable estimates of an appropriate target heart rate zone. When feeling for the carotid pulse under the angle of the jaw, use very light pressure. The radial pulse is felt on the wrist just under the thumb. FIGURE 13.7 Checking your pulse. The pulse can be taken at the carotid artery in the neck (a) or at the radial artery in the wrist (b). Courtesy Robin Mouat After you begin your fitness program, you may improve quickly because the body adapts readily to new exercises. The rate of improvement may slow after the first month or so. The more fit you become, the harder you will have to work to improve. By monitoring your heart rate, you will always know if you are working hard enough to improve, not hard enough, or too hard. For most people, a fitness program involves attaining an acceptable level of fitness and then maintaining that level. There is no need to keep working indefinitely to improve; doing so only increases the chance of injury. After you have reached the level you want, you can maintain fitness by exercising at the same intensity 3-5 days per week. If you have been sedentary, start by exercising at the lower end of your target heart rate range (65% of maximum heart rate) for at least 4-6 weeks. Exercising closer to the top of the range can cause fast and significant gains in maximal oxygen consumption, but you may increase your risk of injury and overtraining. You can achieve significant health benefits by exercising at the bottom of your target range, so don't feel pressure to exercise at an unnecessarily intense level. If you exercise at a lower intensity, you can increase the duration or frequency of training to obtain as much benefit to your health, as long as you are above the 65% training threshold. For people with a very low initial level of fitness, a lower training intensity of 55-64% of maximum heart rate may be sufficient to achieve improvements in maximal oxygen consumption, especially at the start of an exercise program. Intensities of 70-85% of maximum heart rate are appropriate for average individuals. Page 358 By monitoring your heart rate, you will always know if you are working hard enough to improve, not hard enough, or too hard. As your program progresses and your fitness improves, you will need to jog, cycle, or walk faster in order to reach your target heart rate zone. To monitor your heart rate during exercise, count your pulse while you're still moving or immediately after you stop exercising. Count beats for 15 seconds and then multiply that number by 4 to see if your heart rate is in your target zone. Table 13.3 shows target heart rate ranges and 15-second counts based on the maximum heart rate formula. Table 13.3 Target Heart Rate Range and 15-Second Counts AGE (YEARS) TARGET HEART RATE RANGE (bpm)* 15-SECOND COUNT (beats) 20-24 127-180 32-45 25-29 124-176 31-44 30-34 121-171 30-43 35-39 118-167 30-42 40-44 114-162 29-41 45-49 111-158 28-40 50-54 108-153 27-38 55-59 105-149 26-37 60-64 101-144 25-36 65+ 97-140 24-35 *Target heart rates lower than those shown here are appropriate for individuals with a very low initial level of fitness. Ranges are based on the following formula: target heart rate = 0.65 to 0.90 of maximum heart rate, assuming maximum heart rate = 220 ‒ age. Heart rate monitors are useful if close tracking of heart rate is important in your program. They offer several advantages: They are accurate, and they reduce the risk of mistakes when checking your own pulse. They are easy to use, although a sophisticated, multifunction monitor may take some time to master. They do the monitoring for you, so you don't have to worry about checking your own pulse. Heart rate can be integrated into workout information provided by smartphone apps such as Cyclemeter, Strava, Spotify, and Garmin Connect. When shopping for a heart rate monitor, do your homework. Quality, reliability, and warranties vary. Ask personal trainers for recommendations, and look for product reviews in consumer magazines or online. Another way scientists describe fitness is in terms of the capacity to increase metabolism (energy usage level) above rest. Scientists use METs to measure the metabolic cost of an exercise. One MET represents the body's resting metabolic rate—that is, the energy or calorie requirement of the body at rest. Exercise intensity is expressed in multiples of resting metabolic rate. For example, an exercise intensity of 2 METs is twice the resting metabolic rate. Page 359 METs are used to describe exercise intensities for occupational activities and exercise programs. Exercise intensities of less than 3-4 METs are considered low. Household chores and most industrial jobs fall into this category. Exercise at these intensities does not improve fitness for most people, but it will improve fitness for people with low physical capacities. Activities that increase metabolism by 6-8 METs are classified as moderate-intensity exercises and are suitable for most people beginning an exercise program. Vigorous exercise increases metabolic rate by more than 10 METs. Fast running or cycling, as well as intense play in sports like racquetball, can place people in this category. Table 13.4 lists the MET ratings for various activities. Table 13.4 Approximate MET and Caloric Costs of Selected Activities for a 154-Pound Person ACTIVITY METS CALORIC EXPENDITURE (kilocalories/min) Rest 1 1.2 Light housework 2-4 2.4-4.8 Bowling 2-4 2.5-5 Walking 2-7 2.5-8.5 Archery 3-4 3.7-5 Dancing 3-7 3.7-8.5 Hiking 3-7 3.7-8.5 Horseback riding 3-8 3.7-10 Cycling 3-8 3.7-10 Basketball (recreational) 3-9 3.7-11 Swimming 4-8 5-10 Tennis 4-9 5-11 Fishing (fly, stream) 5-6 6-7.5 In-line skating 5-8 6-10 Skiing (downhill) 5-8 6-10 Rock climbing 5-10 6-12 Scuba diving 5-10 6-12 Skiing (cross-country) 6-12 7.5-15 Jogging 8-12 10-15 note: Intensity varies greatly with effort, skill, and motivation. source: Adapted from American College of Sports Medicine. 2013. ACSM's Guidelines for Exercise Testing and Prescription, 9th ed. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins Health. METs are intended to be only an approximation of exercise intensity. Skill, body weight, body fat, and environment affect the accuracy of METs. As a practical matter, however, these limitations can be disregarded. METs are a good way to express exercise intensity because this system is easy for people to remember and apply. Time (Duration) A total time of 20-60 minutes per workout is recommended for cardiorespiratory endurance training. Exercise can be done in a single session or several sessions lasting 10 or more minutes. The total duration of exercise depends on its intensity. To improve cardiorespiratory endurance during a moderate-intensity activity such as walking or slow swimming, you should exercise for 45-60 minutes. For high-intensity exercise performed at the top of your target heart rate zone, a duration of 20 minutes is sufficient. Start with less vigorous activities and gradually increase intensity. Type The best exercises for developing cardiorespiratory endurance stress a large portion of the body's muscle mass for a prolonged period of time. These include walking, jogging, running, swimming, bicycling, and aerobic dance. Many popular sports and recreational activities, such as racquetball, tennis, basketball, and soccer, are also good if the skill level and intensity of the game are sufficient to provide a vigorous workout. The Warm-Up and Cool-Down It is always important to warm up before you exercise and to cool down afterward. Warming up enhances your performance and decreases your chances of injury. Your muscles work better when their temperature is elevated slightly above resting level. Warming up helps your body progress gradually from rest to exercise. Blood needs to be redirected to active muscles, and your heart needs time to adapt to the increased demands of exercise. A warm-up bathes joints with lubricating fluid, which helps protect joint surfaces from wear and tear. A warm-up session should include low-intensity movements similar to those in the activity that will follow. For example, hit forehands and backhands before a tennis game or jog slowly for 400 meters before progressing to an 8-minute mile. Some people like to include stretching exercises in their warm-up, but experts recommend stretching after the active part of your warm-up, when your body temperature is elevated. Studies have found that stretching prior to exercise can temporarily decrease muscle strength and power, so if a high-performance workout is your goal, it is best to stretch after a workout. Stretching is discussed in detail later in this chapter. Cooling down after exercise is important to restore the body's circulation to its normal resting condition. When you are at rest, a relatively small percentage of your total blood volume is directed to muscles, but during exercise, as much as 90% of the heart's output is directed to them. During recovery from exercise, continuing to exercise at a low level is important to provide a smooth transition to the resting state. Cooling down helps regulate the Page 360return of blood to your heart. After exercising, avoid taking a hot shower until you have cooled down. Woman doing a bench press exercise at the gym. Weight training exercises are isotonic (dynamic) exercises that involve applying force with movement. © Glow Wellness/Alamy QUICK STATS 5-10 minutes of warming up and cooling down are adequate for a 30-minute workout of brisk walking. —Centers for Disease Control and Prevention, 2016 Exercises for Muscular Strength and Endurance Any program designed to promote health should include exercises that develop muscular strength and endurance. Your ability to maintain correct posture and move efficiently depends in part on muscle fitness. Strengthening exercises also increase muscle tone, which improves the body's appearance. Types of Strength Training Exercises Muscular strength and endurance can be developed in many ways, from weight training to calisthenics. Common exercises such as curl-ups, push-ups, pull-ups, and nonweighted squats maintain the muscular strength of most people if they practice them several times a week. To condition and tone your whole body, choose exercises that work the major muscles of the shoulders, chest, back, arms, abdomen, and legs. To increase muscular strength and endurance, you must do resistance exercise—exercises in which your muscles must exert force against a significant amount of resistance. Resistance can be provided by weights, exercise machines, your own body weight, or even objects such as rocks. Isometric (static) exercises involve applying force without movement, such as when you contract your abdominal muscles. This type of exercise is valuable for toning and strengthening muscles. Isometrics can be practiced anywhere and do not require any equipment. For maximum strength gains, hold an isometric contraction maximally for 6 seconds, and do 3-10 repetitions. Don't hold your breath: Doing so can restrict blood flow to your heart and brain. Within a few weeks, you will notice the effect of this exercise. Isometrics are particularly useful when recovering from an injury. Isotonic (dynamic) exercises involve applying force with movement, as in weight training exercises such as the bench press. These types of exercises are the most popular for increasing muscle strength and seem to be most valuable for developing strength that can be transferred to other forms of physical activity. They include exercises using barbells, dumbbells, kettlebells, weight machines, and body weight (as in push-ups or pull-ups). Core Training The core muscles include those in the abdomen, pelvic floor, sides of the trunk, back, buttocks, hips, and pelvis (Figure 13.8). They stabilize the midsection when you sit, stand, reach, walk, jump, twist, squat, throw, or bend. During any dynamic movement, the core muscles and active muscles work together. Some shorten to cause movement, whereas others contract and hold to provide stability, lengthen to brake the movement, or send signals to the brain about the movements and positions of the muscles, joints, and bones. When specific core muscles are weak or tired, the nervous system steps in and uses other muscles. This substitution causes abnormal stress on the joints, decreases power, and increases the risk of injury. Superficial and deep abdominal, spinal, trunk, hip, buttocks, pelvis, and pelvic floor muscles. FIGURE 13.8 Major core muscles. source: Fahey, T. D., P. M. Insel, C. E. Insel and W. T. Roth. 2017. Fit and Well: Core Concepts and Labs in Physical Fitness and Wellness, 12th ed. New York: McGraw-Hill. Copyright © 2017 The McGraw-Hill Companies, Inc. For more than 100 years, traditional core training included dynamic exercises such as sit-ups, back extensions, and twists. However, since 2000, scientists have confirmed that spinal stability and stiffness are more important for health and performance than core movement strength. Isometric core exercises like side bridges build core stiffness, which strengthens core muscles and improves their endurance, reduces low back pain, and boosts sports performance. Greater core stiffness transfers strength and speed to the limbs, increases the load-bearing capacity of the spine, and protects the internal organs during sports movements. A series of studies directed by Stuart McGill from the University of Waterloo in Canada showed that isometric exercises for the core resulted in greater core stiffness than did whole-body dynamic exercises that activated core muscles. His studies on core stiffness are changing the way we train for sports. Page 361 The best exercises for low-back health are whole-body exercises that force the core muscles to stabilize the spine in many different directions. Exercises that focus on the core muscles include the lunge, side bridges, stir-the-pot, and bird dogs. These exercises are generally safe for beginning exercisers and, with physician approval, people with back pain. Sex Differences in Muscular Strength Within a given genetic population, men are generally stronger than women because their bodies are typically larger overall and a larger proportion of their total body mass is made up of muscle. But when strength is expressed per unit of muscle tissue, men are only 1-2% stronger than women in the upper body and about equal to women in the lower body. Individual muscle cells are larger in men, but the functioning of the cells is the same in both sexes. Three factors that help explain the strength disparities between men and women are testosterone levels, skeletal size, and nerve-conduction velocity. Testosterone promotes the growth of muscle tissue in both males and females, but testosterone levels are about 6-10 times higher in men than in women, so men develop larger muscles. Also, men are usually bigger than women, which gives them more leverage. Nerve-conduction velocity in the brain is about 4% faster in men than women, which provides a slight advantage in muscle activation speed. Most women will not develop large muscles from strength training. Resistance exercise helps women reduce their overall body fat levels and reduce fat in the midsection. Losing muscle over time is a much greater health concern for women than small gains in muscle weight in response to strength training, especially because any gains in muscle weight are typically more than balanced with loss of fat weight. Men and women lose muscle mass and power as they age, but because men start out with more muscle when they are young and don't lose power as quickly as women, older women often have greater impairment of muscle function than older men. This disparity may partially explain the higher incidence of life-threatening falls in older women. Choosing Equipment Many people prefer weight machines to free weights because they are safe, convenient, and easy to use. You set the resistance, sit down at the machine, and start working. Free weights require more care, balance, and coordination to use, but they strengthen your body in ways that are more adaptable to real life. Choosing Exercises A complete weight training program works all the major muscle groups: neck, upper back, shoulders, arms, chest, core, thighs, buttocks, and calves. Different exercises work different muscles, so it usually takes about 8-10 exercises to get a complete workout for general fitness. For example, you can do bench presses to develop the chest, shoulders, and upper arms; pull-ups to work the biceps and upper back; squats to develop the legs and buttocks; toe raises to work the calves; and so on. If you are also training for a particular sport, include exercises to strengthen the muscles that are important for optimal performance and those that are most likely to be injured. Whole-body functional exercises, such as kettlebell swings and snatches, work many large muscle groups in the lower and upper body. Page 362 Exercising with a kettlebell works large muscle groups in the upper and lower body. © Jordan Siemens/Getty Images RF Frequency For general fitness, the American College of Sports Medicine (ACSM) recommends a strength workout frequency of at least 2 nonconsecutive days per week. This schedule allows your muscles one or more days of rest between workouts to avoid soreness and injury. If you enjoy weight training and would like to train more often, try working different muscle groups on alternate days. Intensity and Time The amount of weight (resistance) you lift in weight training exercises is equivalent to intensity in cardiorespiratory endurance training, and the number of repetitions of each exercise is equivalent to time. To improve fitness, you must do enough repetitions of each exercise to temporarily fatigue your muscles. The number of repetitions needed to cause fatigue depends on the amount of resistance: The heavier the weight, the fewer repetitions to reach fatigue. In general, a heavy weight and a low number of repetitions (1-5) build strength, whereas a light weight and a high number of repetitions (10-25) build endurance. For a general fitness program to build both strength and endurance, try to do 8-12 repetitions of each exercise. For people who are over 50 years of age, 10-15 repetitions of each exercise using a lighter weight is recommended. The first few sessions of weight training should be devoted to learning the exercises. To start, choose a weight that you can move easily through 8-12 repetitions. Add weight when you can do more than 12 repetitions of an exercise. If adding weight means you can do only 7 or 8 repetitions before your muscles fatigue, stay with that weight until you can again complete 12 repetitions. If you can do only 4-6 repetitions after adding weight, or if you can't maintain good form, you've added too much and should take some off. As a general guideline, try increases of approximately a half-pound of additional weight for each 10 pounds you are currently lifting. For developing strength and endurance for general fitness, a single set (a group of repetitions) of each exercise is sufficient, provided you use enough weight to fatigue your muscles. Doing more than one set of each exercise may increase strength development further, and most serious weight trainers do at least three sets of each exercise. If you do more than one set of an exercise, rest long enough between sets (1-5 minutes) to allow your muscles to recover. You should warm up before every weight training session and cool down afterward. You can expect to improve rapidly during the first 6-10 weeks of training; gains will then come more slowly. Factors such as age, motivation, sex, and genetics will affect your progress. Your ultimate goal depends on you. After you have achieved the level of strength and muscularity that you want, you can maintain your gains by training 2 or 3 nonconsecutive days per week. A Caution about Supplements No nutritional supplement or drug will change a weak person into a strong person. Those changes require regular training that stresses the body and causes physiological adaptations. Supplements or drugs that promise quick, large gains in strength usually don't work and are often dangerous, expensive, or illegal. Over-the-counter supplements are not regulated carefully, and their long-term effects have not been studied systematically. Performance-enhancing drugs such as anabolic steroids and growth hormone have potentially dangerous side effects. Flexibility Exercises Flexibility, or stretching, exercises are important for maintaining the normal range of motion in the major joints of the body. Some exercises, such as running, can decrease flexibility because they require only a partial range of motion. Like a good weight training program, a good stretching program includes exercises for all the major muscle groups and joints of the body: neck, shoulders, back, hips, thighs, hamstrings, and calves. In tandem with core training, flexibility training is important for preventing low-back injuries and maintaining low-back health. Proper Stretching Technique Timing determines the best stretching technique: In general, do static stretching after a workout and dynamic or active stretching before a workout. Static stretching involves extending to a certain position and then holding it. Dynamic stretching is done by actively moving through the joints' ranges of motion. Ballistic stretchingPage 363 (known as "bouncing") is dangerous and counterproductive. The safest and most convenient technique for increasing flexibility may be active static stretching with a passive assist. For example, you might do a seated stretch of your calf muscles by contracting the muscles on the top of your shin and by grabbing your feet and pulling them toward you. When performed regularly, stretching exercises help maintain or improve the range of motion in joints. © Brian Caissie/Getty Images RF Frequency Do stretching exercises at least 2 or 3 days per week (but 5-7 days is optimal). If you stretch during your cool-down after cardiorespiratory endurance exercise or strength training, you may develop more flexibility because your muscles are warmer then and can be stretched farther. Intensity and Time Do stretching exercises statically. Stretch to the point of mild discomfort, hold the position for 10-30 seconds, rest for 30-60 seconds, and then repeat, trying to stretch a bit farther. Stretch each muscle group for a total of 60 seconds. Older adults might benefit more from holding a stretch for 30-60 seconds. Increase your intensity gradually over time. Improved flexibility takes many months to develop. There are large individual differences in joint flexibility. Don't feel you have to compete with others during stretching workouts. Training in Specific Skills The final component in your fitness program is learning the skills required for the sports or activities in which you choose to participate. By taking the time and effort to acquire competence, you can achieve a sense of mastery and add a new physical activity to your repertoire. The first step in learning a new skill is getting help. Sports like tennis, golf, and skiing require mastery of basic movements and techniques, so instruction from a qualified teacher or coach can save you hours of frustration and increase your enjoyment. Skill is also important in conditioning activities such as jogging, swimming, and cycling. Even if you learned a sport as a child, additional instruction now can help you refine your technique, get over stumbling blocks, and relearn skills that you may have learned incorrectly. Putting It All Together Now that you know the basic components of a fitness program, you can put them all together in a program that works for you. Remember to include the following: Cardiorespiratory endurance exercise. Do at least 150 minutes of moderate-intensity aerobic exercise or 75 minutes of vigorous-intensity exercise per week (or a combination). Muscular strength and endurance. Work the major muscle groups (one or more sets of 8-10 exercises) at least 2-3 nonconsecutive days a week. Flexibility exercise. Do stretches at least 2 or 3 days a week and ideally 5-7 days a week, preferably after exercise when your muscles are warm. Skill training. Incorporate some or all of your aerobic or strengthening exercise into an enjoyable sport or physical activity. See Figure 13.9 for a summary of the FITT principle for the health-related components of fitness. FITT recommendations for Cardiorespiratory Endurance Training, Strength Training, and Flexibility Training. [D] FIGURE 13.9 A summary of the FITT principle for the health-related components of fitness.

getting started and staying on track

Page 364 GETTING STARTED AND STAYING ON TRACK Once you have a program that fulfills your basic fitness needs and suits your personal tastes, adhering to a few basic principles will help you improve quickly, have fun, and minimize the risk of injury. These principles include buying appropriate equipment, eating and drinking properly, and managing your program so that it becomes an integral part of your life. Selecting Instructors, Equipment, and Facilities Once you've chosen the activities for your program, you may need to look for the appropriate information, instruction, and equipment or find an appropriate facility. Finding Help and Advice One of the best places to get help is an exercise class, where an expert instructor can teach you the basics of training and answer your questions. A qualified personal trainer can also get you started on an exercise program or a new form of training. Make sure that your instructor or trainer has proper qualifications, such as a college degree in exercise physiology, kinesiology, or physical education and certification by the American College of Sports Medicine, National Strength and Conditioning Association, International Sports Science Association, or another professional organization. Don't seek out a person for advice simply because he or she looks fit. You can further your knowledge by reading articles by experts in fitness magazines such as Fitness Rx for Men and Fitness Rx for Women. Many websites provide fitness programs, including ongoing support and feedback via e-mail. Many of these sites charge fees, so it is important to review the sites, decide which ones seem most appropriate, and if possible go through a free trial period before subscribing. Also remember to consider the reliability of the information at fitness websites, especially those that also advertise or sell products. A few popular sites are listed in the "For More Information" section at the end of the chapter. QUICK STATS More than 54 million Americans used health clubs in 2014, an increase of 40% since 2000. —International Health, Racquet & Sportsclub Association, 2016 Selecting Equipment Good equipment will enhance your enjoyment and decrease your risk of injury. Appropriate safety equipment, such as pads and helmets for skateboarding, is particularly important. If you shop around, you can often find bargains through mail-order companies and discount or used equipment stores. Before you invest in a new piece of equipment, investigate it. Try it out at a local gym to make sure that you'll use it regularly. Make sure you have space to use and store it at home. Ask the experts (coaches, physical educators, and sports instructors) for their opinions. Also, educate yourself and become a lifelong student of physical activity and sport. Footwear is an important piece of equipment for almost any activity; see the box "What to Wear" for shopping strategies. CRITICAL CONSUMER: What to Wear Clothing Modern exercise clothing is attractive, comfortable, and functional. Shorts made of elastic material, such as spandex, hug the body, supplying support. If you prefer, you can wear running shorts and a T-shirt. The main requirement for workout clothes is that they let you move easily but are not so loose that they get caught in the exercise machines or on fences when running outside. Don't wear street clothes when exercising because they can interfere with movement, and sweat, oil, and dirt can ruin them. If you run or cycle on the street, wear bright-colored clothing so that motorists can see you, and cyclists should wear a helmet to prevent head injury in case of an accident. Specifics for Women and Men For women. Wear a good sports bra whenever you exercise. Breast support is important when running, playing volleyball, or weight training, The breasts can be injured if barbells press too firmly against them when you are weight-training or if they aren't properly supported when you run. A good sports bra should support the breasts in all directions, contain minimal elastic material, absorb moisture freely, and be easily laundered. Seams, hooks, and catches should not irritate the skin. You might consider buying a bra with an underwire for added support and a pocket in which to insert padding if you do exercises that could cause injury. For men. Wear a protective cup and jockstrap when participating in contact sports, such as football, baseball, cricket, hockey, wrestling, and karate. These protections can help guard against male infertility. Footwear Footwear is perhaps the most important item of equipment for almost any activity. Shoes protect and support your feet and improve traction. When you jump or run, you place as much as six times more force on your feet than when you stand still. Shoes can help cushion against the stress that this additional force places on your lower legs, thereby preventing injuries. Some athletic shoes are also designed to help prevent ankle rollover, another common source of injury. When choosing athletic shoes, first consider the activity you've chosen for your exercise program. Shoes appropriate for different activities have different characteristics. Foot type is another important consideration. If your feet tend to roll inward excessively, you may need additional stability features on the inner side of the shoe to counteract this movement. If your feet tend to roll outward excessively, you may need highly flexible and cushioned shoes that promote foot motion. Most women will get a better fit if they choose shoes that are specially designed for women's feet rather than downsized versions of men's shoes. Barefoot Shoes or Minimalist Footwear Two-thirds of runners experience an injury every year. Humans have evolved to run, so some scientists blame running shoes for the high injury rate. Most runners strike heel first when using heavily padded running shoes. Barefoot runners strike the ground with their forefoot (at least they're supposed to), which better uses the shock absorbing capacity of the skeleton. Some researchers speculated that using "minimalist" footwear allows people to run more naturally, which should cut down on the injury rate. Other research suggests that traditional running shoes provide a physiological advantage that makes running easier. We need more research to determine whether barefoot running is safe and viable or just the latest running fad. Labeled parts of a running shoe. [D] © Photodisc Successful Shopping For successful shoe shopping, keep the following strategies in mind: Shop late in the day or, ideally, following a workout. Your foot size increases during the day and after exercise. Wear socks like those you plan to wear during exercise. Try on both shoes and wear them around for 10 minutes or more. Try walking on an uncarpeted surface. Approximate the movements of your activity: walk, jog, run, jump, and so on. Check the fit and style carefully: Is the toe box roomy enough? Your toes will spread out when your foot hits the ground or you push off. There should be at least one thumb's width of space from the longest toe to the end of the toe box. Do the shoes have enough cushioning? Do your feet feel supported when you bounce up and down? Try bouncing on your toes and on your heels. Do your heels fit snugly in the shoe? Do they stay put when you walk, or do they slide up? Are the arches of your feet on top of the shoes' arch supports? Do the shoes feel stable when you twist and turn on the balls of your feet? Try twisting from side to side while standing on one foot. Do you feel any pressure points? If you exercise at dawn or dusk, choose shoes with reflective sections for added visibility and safety. Replace athletic shoes about every three months or 300-500 miles of jogging or walking. Choosing a Fitness Center Are you thinking of joining a health club or fitness center? Be sure to choose one that has the right programs and equipment available at the times you will use them. You should feel comfortable with the classes and activities available; the age, fitness level, and dress of others in the club; and the types of music used in classes. The facility and equipment should be clean and well maintained, including the showers and lockers. The staff should be well trained and helpful. Also make sure the facility is certified. Look for the displayed names American College of Sports Medicine, National Strength and Conditioning Association, American Council on Exercise, or Aerobics and Fitness Association of America. These trade associations have established standards to help protect consumer health, safety, and rights. Eating and Drinking for Exercise Most people do not need to change their eating habits when they begin a fitness program. Many athletes and other physically active people are lured into buying aggressively advertised vitamins, minerals, and protein supplements, but in most cases a well-balanced diet contains all the energy and nutrients needed to sustain an exercise program (see Chapter 12). A balanced diet is also the key to improving body composition when you begin to exercise more. One of the promises of a fitness program is a decrease in body fat and an increase in muscle mass. As a general rule, if you consume more calories than you expend through metabolism and exercise, fat increases. However, the control of body fat is determined by the amount and kind of calories you consume. Reduce your intake of added sugars and trans fats, and be physically active. One of the most important principles to follow when exercising is to keep your body well hydrated by drinking enough fluids. Your body depends on water to sustain many chemical reactions and to maintain correct body temperature. Sweating during exercise depletes the body's water supply and can lead to dehydration if fluids are not replaced. Serious dehydration can cause reduced blood volume, accelerated heart rate, elevated body temperature, muscle cramps, heat stroke, and other serious problems. Page 366 Drinking fluids before and during exercise is important to prevent dehydration and enhance performance. Thirst receptors in the brain make you want to drink fluids, but during heavy or prolonged exercise or exercise in hot weather, thirst alone isn't a good indication of how much fluid you need to drink. As a rule of thumb, drink at least 16 ounces of fluid two to four hours before exercise and then drink enough during exercise to prevent significant fluid loss in sweat. Don't drink more than one quart per hour during exercise. After exercise, let thirst be your guide to your fluid needs. You can also check your weight before and after an exercise session; any weight loss is due to fluid loss that needs to be replaced. Carry fluids when you exercise so that you can replace your fluids when they're depleted. For exercise sessions lasting less than 60-90 minutes, cool water is an excellent fluid replacement. For longer workouts, ACSM recommends a sports drink that contains water and small amounts of electrolytes (sodium, potassium, and magnesium) and simple carbohydrates (sugar, usually in the form of sucrose or glucose). After your workout, replace any lost fluids. Nonfat or low-fat milk, for those who can tolerate dairy products, are excellent post-exercise fluid replacement beverages because they promote long-term hydration. Milk is digested more slowly than water or sports beverages and also contains electrolytes. Managing Your Fitness Program How can you tell when you're in shape? When do you stop improving and start maintaining? How can you stay motivated? For your program to become an integral part of your life, these questions are key. Starting Slowly, Getting in Shape Gradually As Table 13.5 shows, an exercise program can be divided into three phases: Beginning phase. The body adjusts to the new type and level of activity. Progress phase. Fitness increases. Maintenance phase. The targeted level of fitness is sustained over the long term. Table 13.5 Sample Progression for an Endurance Program STAGE/WEEK FREQUENCY (days/week) INTENSITY* (beats/minute) TIME (duration in minutes) Initial stage 1 3 120-130 15-20 2 3 120-130 20-25 3 4 130-145 20-25 4 4 130-145 25-30 Improvement stage 5-7 3-4 145-160 25-30 8-10 3-4 145-160 30-35 11-13 3-4 150-165 30-35 14-16 4-5 150-165 30-35 17-20 4-5 160-180 35-40 21-24 4-5 160-180 35-40 Maintenance stage 25+ 3-5 160-180 20-60 *The target heart rates shown here are based on calculations for a healthy 20-year-old. The program progresses from an initial target heart rate of 50% to a maintenance range of 70-90% of maximum heart rate. source: Adapted from American College of Sports Medicine. 2013. ACSM's Guidelines for Exercise Testing and Prescription, 9th ed. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins Health. When beginning a program, start slowly to give your body time to adapt to the stress of exercise. Choose activities carefully according to your fitness status. Exercising Consistently Consistency is the key to getting into shape without injury. Steady fitness improvement comes when you overload your body consistently over time. The best way to ensure consistency is to record the details of your workouts in a journal: how far you ran, how much weight you lifted, and so on. This record will help you evaluate your progress and plan workout sessions intelligently. Don't increase your exercise volume by more than 5-10% per week. Table 13.5 shows how the amount of overload is increased gradually over time in a sample walking-running program. Regardless of the activity chosen, an exercise program must begin slowly and progress gradually. Once you achieve the desired level of fitness, you can maintain it by exercising 3-5 days a week. Assessing Your Fitness When are you in shape? It depends. One person may be out of shape running a mile in 5 minutes, but another may be in shape running a mile in 12 minutes. As mentioned earlier, your ultimate level of fitness depends on your goals, your program, and your natural ability. The important thing is to set goals that make sense for you. To assess your own approximate level of cardiorespiratory endurance, take the test in the box "The 1.5-Mile Run-Walk Test." ASSESS YOURSELF: The 1.5-Mile Run-Walk Test You can obtain a general rating of your cardiorespiratory fitness by taking the 1.5-mile run-walk test. Don't attempt this test unless you have completed at least 6 weeks of some type of conditioning activity. Also, if you are over age 35 or have questions about your health, check with your physician before taking this test. You'll need a stopwatch, clock, or watch with a second hand and a running track or course that is flat and provides measurements of up to 1.5 miles. You may want to practice pacing yourself before taking the test to avoid going too fast at the start and becoming fatigued before you finish. Allow yourself a day or two to recover from a practice run before taking the test. Warm up before taking the test with some walking, easy jogging, and stretching exercises. The idea is to cover the distance as fast as possible at a pace that is comfortable for you. You can run or walk the entire distance or use some combination of running and walking. If possible, monitor your own pace, or have someone call out your time at various intervals to help you determine whether your pace is correct. When you have completed the test, refer to the table for your cardiorespiratory fitness rating. Be sure to cool down by walking or jogging slowly for about 5 minutes. Standards for the 1.5-Mile Run-Walk Test (Minutes: Seconds) Superior Excellent Good Fair Poor Very Poor Women Age: 18-29 11:00 or less 11:01-12:59 13:00-14:29 14:30-15:59 16:00-17:29 17:30 or more 30-39 11:45 or less 11:46-13:29 13:30-15:29 15:30-16:29 16:30-18:29 18:30 or more 40-49 12:45 or less 12:46-14:29 14:30-16:29 16:30-18:29 18:30-19:29 19:30 or more 50-59 14:15 or less 14:16-16:29 16:30-18:29 18:30-19:29 19:30-20:29 20:30 or more 60 and over 16:29 or less 16:30-17:29 17:30-19:29 19:30-20:29 20:30-20:59 21:00 or more Men Age: 18-29 9:15 or less 9:16-10:29 10:30-11:59 12:00-12:59 13:00-14:14 14:15 or more 30-39 9:45 or less 9:46-10:59 11:00-12:29 12:30-13:44 13:45-14:59 15:00 or more 40-49 10:00 or less 10:01-11:59 12:00-12:59 13:00-14:29 14:30-15:59 16:00 or more 50-59 10:45 or less 10:46-12:59 13:00-14:29 14:30-15:59 16:00-17:59 18:00 or more 60 and over 11:15 or less 11:16-13:59 14:00-15:59 16:00-17:59 18:00-20:59 21:00 or more source: Adapted from The Aerobics Program for Total Well Being by Kenneth H. Cooper, M.D., M.P.H. Bantam Books, 1982. Preventing and Managing Athletic Injuries Although they are annoying, most injuries are neither serious nor permanent. If an injury is not cared for properly, however, it can escalate into a chronic problem. If you learn how to deal with injuries, they won't derail your fitness program (Table 13.6).Page 367 Table 13.6 Care of Common Exercise Injuries and Discomforts INJURY SYMPTOMS TREATMENT Blister Accumulation of fluid in one spot under the skin Don't pop or drain it unless it interferes too much with your daily activities. If it does pop, clean the area with antiseptic and cover with a bandage. Do not remove the skin covering the blister. Bruise (contusion) Pain, swelling, and discoloration R-I-C-E: rest, ice, compression, elevation. Fracture and/or dislocation Pain, swelling, tenderness, loss of function, and deformity Seek medical attention, immobilize the affected area, and apply cold. Joint sprain Pain, tenderness, swelling, discoloration, and loss of function R-I-C-E. Apply heat about 2 days after injury. Stretch and strengthen affected area. Muscle cramp Painful, spasmodic muscle contractions Gently stretch for 15-30 seconds at a time and/or massage the cramped area. Drink fluids and increase dietary salt intake if exercising in hot weather. Muscle soreness or stiffness Pain and tenderness in the affected muscle Stretch the affected muscle gently; exercise at a low intensity; apply heat. Muscle strain Pain, tenderness, swelling, and loss of strength in the affected muscle R-I-C-E. Apply heat about 2 days after injury. Stretch and strengthen the affected area. Plantar fasciitis Pain and tenderness in the connective tissue on the bottom of the foot Apply ice and stretch. Wear night splints when sleeping. Shin splint Pain and tenderness on the front of the lower leg; sometimes also pain in the calf muscle Rest. Apply ice or heat to the affected area several times a day and before exercise; wrap with tape for support. Stretch and strengthen muscles in the lower legs. Purchase good-quality footwear and run on soft surfaces. Side stitch Pain on the side of the abdomen Stretch the arm on the affected side as high as possible; if that doesn't help, try bending forward while tightening the abdominal muscles. Tendinitis Pain, swelling, and tenderness of the affected area R-I-C-E. Apply heat about 2 days after injury. Stretch and strengthen the affected area. source: Fahey, T. D., et al. 2017. Fit and Well: Core Concepts and Labs in Physical Fitness and Wellness, 12th ed. New York: McGraw-Hill. Copyright © 2017 The McGraw-Hill Companies, Inc. Some injuries require medical attention. See a physician right away if you suffer a head or eye injury, a possible ligament injury, a broken bone, or an internal disorder such as chest pain, fainting, or intolerance to heat. Also seek medical attention for apparently minor injuries that do not get better within a reasonable amount of time. For minor cuts and scrapes, stop the bleeding and clean the wound with soap and water. Treat soft tissue injuries (muscles and joints) with the R-I-C-E principle: Rest: Stop using the injured tissue as soon as you experience pain, protect it from further injury, and avoid any activity that causes pain. Ice: Ice reduces bleeding, but it also decreases inflammation, new blood vessel formation, and release of tissue growth factors. Ice decreases pain and spasm following an injury, but it might delay healing and eventual return to the playing field, so use it only during the early phases of injury rehabilitation. Apply ice to the injured tissue to reduce swelling and alleviate pain. Apply ice immediately for 10-20 minutes, and repeat every few hours until the swelling disappears.Page 368 Compression: Wrap the injured area with an elastic or compression bandage between icings. If the area starts throbbing or begins to change color, the bandage may be wrapped too tightly. Do not sleep with the bandage on. Elevation: Raise the injured area above heart level to decrease the blood supply and reduce swelling. After 36-48 hours, if the swelling has disappeared, apply heat to relieve pain, relax muscles, and reduce stiffness. Immerse the affected area in warm water or apply warm compresses, a hot water bottle, or a heating pad. After a minor athletic injury, gradually reintroduce the stress of the activity until you can return to full intensity. Before returning to full exercise participation, you should have a full range of motion in your joints; normal strength and balance; no injury compensation movements, such as limping; and little or no pain. To prevent injuries, follow six basic guidelines: Stay in condition: Haphazard exercise programs invite injury. Warm up thoroughly before exercising. Use proper body mechanics when lifting objects or executing sports skills. Don't exercise when you're ill or overtrained (experiencing extreme fatigue due to overexercising). Use the proper equipment. Don't return to your normal exercise program until athletic injuries have healed. You can minimize the risk of injury by following safety guidelines, respecting signals from your body that something may be wrong, and treating injuries promptly. Use special caution in heat or humidity (over 80°F and over 60% humidity): Exercise slowly, rest frequently in the shade, wear clothing that breathes, and drink plenty of fluids. Slow down or stop if you begin to feel uncomfortable. During hot weather, exercise in the early morning or evening when temperatures are lowest. Staying with Your Program Once you have attained your desired level of fitness, you can maintain it by exercising regularly at a consistent intensity, 3-5 days a week. You must work at the intensity that brought you to your desired fitness level. If you don't, your body will become less fit because less is expected of it. In general, if you exercise at the same intensity over a long period, your fitness will level out and can be maintained easily. Adapt your program to changes in environment or schedule. Don't use wet weather or a new job as an excuse to give up your fitness program. If you walk in the summer, dress appropriately and walk in the winter as well. (Exercise is usually safe even in very cold temperatures as long as you dress warmly in layers and don't stay out too long.) If you can't go out because of darkness or an unsafe neighborhood, walk in a local shopping mall or on campus or join a gym and walk on a treadmill. Page 369 What if you run out of steam? Although good health is an important reason to exercise, it's a poor motivator. You'll find specific suggestions for staying with your program in the Behavior Change Strategy box at the end of the chapter. Cross-training can add variety to your workouts. Cross-training emphasizes whole-body, high-intensity training using exercises such as deadlifts, cleans, squats, presses, jerks, kettlebell exercises, snatches, plyometrics, sled pulls, and weight carrying. Cross trainers learn to handle their bodyweight by practicing gymnastics, pull-ups, dips, kettlebell swings and snatches, rope climbing, push-ups, Olympic lifts, handstands, pirouettes, flips, and splits. They also do aerobics such as running, cycling, rope skipping, and rowing, but the emphasis is on speed and intensity. Cross-training programs, such as CrossFit, attempt to develop well-rounded fitness by including exercises that build cardiovascular and respiratory endurance, stamina, strength, flexibility, power, speed, coordination, agility, balance, and accuracy. Explore many exercise options. Consider competitive sports at the recreational level, or find out how you can participate in an activity you've never done before. Try new activities, especially ones that you will be able to do for the rest of your life. Ask Yourself QUESTIONS FOR CRITICAL THINKING AND REFLECTION Think of a few physical activities and sports that you would like to do, but haven't. Given your current fitness and skill level, which ones could you reasonably incorporate into your exercise program?

the benefits of exercise

THE BENEFITS OF EXERCISE The human body is adaptable. The greater the demands, the more it adjusts and the more fit it becomes. Over time, immediate, short-term adjustments translate into long-term changes and improvements (Figure 13.1). Detailed list of benefits of exercise by organ and body system. [D] FIGURE 13.1 Health benefits of exercise. © PeopleImages/Getty Images RF Reduced Risk of Premature Death Physically active people have a reduced risk of dying prematurely from all causes; the most active people experience the greatest health benefits (Figure 13.2). Image details [D] VITAL STATISTICS FIGURE 13.2 Exercise promotes longevity. Poor muscle strength increases the risk of premature death. sources: Adapted from a composite of 13 studies involving more than 200,000 men and women. Arem, H., et al. 2015. Leisure time physical activity and mortality: A detailed pooled analysis of the dose-response relationship. JAMA 175(6): 959-967; Physical Activity Guidelines Advisory Committee. 2008. Physical Activity Guidelines Advisory Committee Report, 2008. Washington, DC: U.S. Department of Health and Human Services. Page 344 Improved Cardiorespiratory Functioning Every time you take a breath, oxygen enters your lungs and is picked up by red blood cells and transported to your heart. From there, the heart pumps oxygenated blood throughout the body to organs and tissues that use it. During exercise, the cardiorespiratory system (heart, lungs, and circulatory system) must work harder to meet the body's increased demand for oxygen. Regular cardiorespiratory endurance exercise improves the functioning of the heart and the ability of the cardiorespiratory system to carry oxygen to body tissues. Exercise directly affects the health of your arteries, keeping them from stiffening or clogging with plaque and reducing the risk of cardiovascular disease. Exercise also improves sexual function and general vitality. More Efficient Metabolism and Improved Cell Health Endurance exercise improves metabolism—the process that converts food to energy and builds tissue. This process involves oxygen, nutrients, hormones, and enzymes. A physically fit person's body can more efficiently use energy from carbohydrates Page 345and fats and better regulate hormones. Exercise may also protect cells from damage from free radicals, which are destructive chemicals produced normally during metabolism (see Chapter 12), and from inflammation caused by obesity, high blood pressure or cholesterol, nicotine, and overeating. Training activates antioxidants that prevent free radical damage and maintain cell health. Regular physical activity prevents the deterioration of telomeres, which form the protective ends of chromosomes that are vital for cell health and repair. Improved Body Composition Healthy body composition means that the body has a high proportion of fat-free mass and a relatively small proportion of fat. Too much body fat, particularly abdominal fat, is linked to a variety of health problems, including heart disease, high blood pressure, cancer, and diabetes. Healthy body composition can be difficult to achieve and maintain because a diet that contains enough essential nutrients can be relatively high in calories, especially for someone who is sedentary. Excess calories can be stored in the body as fat. Exercise can improve body composition in several ways. Endurance exercise significantly increases daily calorie expenditure. It can also slightly raise metabolic rate, the rate at which the body burns calories, for several hours after an exercise session. Strength training increases muscle mass, thereby tipping the body composition ratio toward fat-free mass and away from fat. It can also help with losing fat because metabolic rate is directly proportional to fat-free mass: The more muscle mass, the higher the metabolic rate. Physical activity reduces the risk of death regardless of its effect on body composition. That is, greater levels of activity are associated with lower death rates, no matter your weight, although this effect is especially true for people who are overweight or obese. A counterintuitive finding from a 1998 study of death rates among men is that "being fat and fit is better than unfat and unfit" (Figure 13.3). A 2015 study of 1.3 million Swedish men, however, found that men who were overweight as young men had a higher risk of premature death, regardless of fitness. Physical activity does not eliminate the health risks associated with overweight, but it reduces its effects. Those who are fit have a lower relative risk of death compared to those who are unfit among those who are normal weight, overweight, and obese. VITAL STATISTICS FIGURE 13.3 Relationship among fitness, body weight, and risk of death among men. source: Adapted from Hainer, V., et al. 2009. Fat or fit: What is more important? Diabetes Care 32(Suppl. 2): s392-s397. Disease Prevention and Management Regular physical activity lowers your risk of many chronic, disabling diseases. Cardiovascular Disease A sedentary lifestyle is one of six major risk factors for cardiovascular disease (CVD), including heart attack and stroke. The other major risk factors are smoking, abnormal blood fats, high blood pressure, diabetes, and obesity. Most of these risk factors are linked by a group of symptoms called the metabolic syndrome. These symptoms include insulin resistance, high blood pressure, abnormal blood fats, abdominal fat deposits, type 2 diabetes, blood clotting abnormalities, and blood vessel inflammation. Sedentary people have CVD death rates significantly higher than those of fit individuals. Physical inactivity increases the risk of CVD by as much as 240%. (See Chapter 15 for an in-depth discussion of cardiovascular disease and its risk factors.) The benefits of physical activity begin at moderate levels of exercise and increase as the amount and intensity of activity rise. Exercise positively affects the risk factors for Page 346CVD, including cholesterol levels, insulin resistance, and blood pressure. Exercise also directly interferes with the disease process itself, lowering the risk of heart disease and stroke. Blood Fat Levels High concentrations of lipids (fats), such as cholesterol and triglycerides, are linked to heart disease because they contribute to the formation of fatty deposits on the linings of arteries. When blood clots block a narrowed artery, a heart attack or stroke can occur. Cholesterol is carried in the blood by lipoproteins, which are classified according to size and density. Cholesterol carried by low-density lipoproteins (LDLs) sticks to the walls of coronary arteries. High-density lipoproteins (HDLs) pick up excess cholesterol in the bloodstream and carry it back to the liver for excretion from the body. High LDL levels and low HDL levels increase the risk of cardiovascular disease. Cardiorespiratory endurance exercise and strength training influence blood lipids in a positive way by increasing HDL and decreasing LDL and triglycerides—reducing the risk of CVD. High Blood Pressure Regular cardiorespiratory endurance exercise tends to reduce high blood pressure (hypertension), a contributing factor in diseases such as coronary heart disease, stroke, heart failure, kidney failure, sexual dysfunction, and blindness. Intense, long-duration exercise works best, but even moderate-intensity exercise can produce significant improvements. Strength training also reduces resting blood pressure. Coronary Heart Disease Coronary heart disease (CHD) involves blockage of one of the coronary arteries. These blood vessels supply the heart with oxygenated blood. An obstruction in a coronary artery can cause a heart attack. Exercise directly interferes with the disease process that causes coronary artery blockage. It also enhances the function of cells lining the arteries that help regulate blood flow. Stroke The most common kind of stroke occurs when a blood vessel leading to the brain is blocked or leaks, often through the same disease process that leads to heart attacks. Regular exercise reduces the risk of stroke. Cancer Studies have shown a relationship between increased physical activity and a reduced risk of cancer. Specifically, a new analysis of data from studies of 1.44 million subjects concludes that higher levels of leisure-time physical activity were associated with lower risks for 13 of 26 types of cancer, including kidney, colon, head and neck, bladder, rectal, and liver cancer. Most of these associations applied whether or not the participants were overweight/obese or had a history of smoking. Exercise may decrease the risk of colon cancer by speeding the movement of food through the gastrointestinal tract (quickly eliminating potential carcinogens), lowering blood-insulin levels, enhancing immune function, and reducing blood fats. Physical activity during high school and college years may be particularly important for preventing breast cancer later in life. Osteoporosis A special benefit of exercise, especially for women, is protection against osteoporosis, a disease that results in loss of bone density and poor bone strength. Weight-bearing exercise, which includes almost everything except swimming, helps build bone during childhood and the teens and twenties. Older people with denser bones can better endure the bone loss that occurs with aging. Strength training and impact exercises such as jumping rope help maintain bone and muscle health throughout life. With stronger bones and muscles and better balance, fit people are less likely to experience debilitating falls and bone fractures. Along with exercise, a well-balanced diet containing adequate calcium and vitamin D and normal hormone function are also essential for strong bones. (One caution: Too much exercise can depress levels of estrogen, which helps maintain bone density, thereby leading to bone loss, even in young women.) Type 2 Diabetes People with diabetes are prone to heart disease, blindness, and severe problems of the nervous and circulatory systems. Exercise prevents type 2 diabetes, the most common form of the disease. Exercise burns excess sugar and makes cells more sensitive to insulin. When people have a condition called insulin resistance, the body produces insulin but fails to use it effectively. Instead of the insulin enabling their cells to absorb and burn excess calories, insulin-resistant people store the excess calories as fat. Exercise helps keep body fat at healthy levels, which is important because obesity is a key risk factor for type 2 diabetes. For people who have diabetes, physical activity is an important part of treatment. See Chapter 14 for more about diabetes. QUICK STATS 75,578 Americans died from diabetes in 2014, making it the seventh leading cause of death that year. —Centers for Disease Control and Prevention, 2016 Improved Psychological and Emotional Wellness Physically active people enjoy many social, psychological, and emotional benefits, including the following: Reduced anxiety. Exercise reduces symptoms of anxiety, such as worry and self-doubt, both in people who are anxious most of the time and in people who become anxious in response to a particular experience. Exercise is associated with a lower risk for panic attacks, generalized anxiety disorder, and social anxiety disorder. Reduced depression and improved mood. Exercise relieves feelings of sadness and hopelessness and can be as effective as psychotherapy in treating mild to moderate cases of depression. Exercise improves mood and increases feelings of well-being in both depressed and nondepressed people.Page 347 Improved sleep. Regular physical activity helps people fall asleep more easily; it also improves sleep quality. Reduced stress. Exercise reduces the body's overall response to all forms of stressors and helps people deal more effectively with stress. Enhanced self-esteem, self-confidence, and self-efficacy. Exercise can boost self-esteem and self-confidence by providing opportunities for people to succeed and excel. Exercise also improves body image. Sticking with an exercise program increases people's belief in their ability to be active, thereby boosting self-efficacy. Enhanced creativity and intellectual functioning. In studies of people of all ages, physically active people score higher than sedentary people on tests of creativity and mental function. Exercise improves alertness and memory in the short term. Over time, exercise helps maintain reaction time, short-term memory, and nonverbal reasoning skills and enhances brain metabolism. Improved work productivity. Studies show that workers' quality of work, time management abilities, and mental and interpersonal performance are better on days they exercise. Increased opportunities for social interaction. Exercise provides many chances for people to have positive interactions with other people. Because exercise improves workers' quality of work and mental and physical abilities, many large companies provide on-site fitness facilities or gym memberships as employee benefits. © Comstock Images/Jupiter images RF Improved Immune Function Exercise can have either positive or negative effects on the immune system—the physiological processes that protect us from disease. Moderate endurance exercise boosts immune function, whereas excessive training depresses it. Physically fit people get fewer colds and upper respiratory tract infections than people who are not fit. The immune system and ways to strengthen it are discussed further in Chapter 17. Prevention of Injuries and Low-Back Pain Increased muscle strength and endurance provide protection against injury because they help people maintain spinal stability, good posture, and appropriate body mechanics when performing everyday activities such as walking, lifting, and carrying. Good muscle endurance in the abdomen, hips, lower back, and legs supports the back in proper alignment and helps prevent low-back pain, which afflicts more than 85% of Americans at some time in their lives. Improved Wellness for Life Although people differ in the maximum levels of fitness they can achieve through exercise, the wellness benefits of exercise are available to everyone. Exercising regularly may be the single most important thing you can do now to improve the quality of your life in the future. All the benefits of exercise continue to accrue but gain new importance as the resilience of youth begins to wane. Simply stated, exercising can help you live a longer and healthier life.