Chapter 6 Adaptations to Aerobic Training
Acute Responses to Aerobic Exercise: •Respiratory responses
-Aerobic exercise provides for the greatest impact on both oxygen uptake and carbon dioxide production, as compared to other types of exercise. -Significant increases in oxygen delivered to the tissue, carbon dioxide returned to the lungs, and minute ventilation provide for appropriate levels of alveolar gas concentrations during aerobic exercise.
Chronic Adaptations to Aerobic Exercise: Neural Adaptations
-Efficiency is increased and fatigue of the contractile mechanisms is delayed.
Two physiological mechanisms are responsible for the regulation of stroke volume.
-End-diastolic volume (the volume of blood available to be pumped by the left ventricle at the end of the filling phase, or diastole_ -The action of catecholamines including epinephrine and norepinephrine, which are hormones of the sympathetic nervous system. Just before and at the beginning of an exercise session, a reflex or anticipatory stimulation of the sympathetic nervous system results in an increase in heart rate.
•Cardiovascular responses in overtraining
-Greater volumes of training affect heart rate.
Acute Responses to Aerobic Exercise: Other Cardiovascular Responses
-Heart rate increases linearly with increases in intensity -Oxygen uptake (the amount of oxygen consumed by the body's tissues) •Increases during an acute bout of aerobic exercise •Is directly related to the mass of exercising muscle, metabolic efficiency, and exercise intensity
•Biochemical responses to overtraining
-High training volume results in increased levels of creatine kinase, indicating muscle damage. -Muscle glycogen decreases with prolonged periods of overtraining.
•Detraining
-If inactivity, rather than proper recovery, follows exercise, an athlete loses training adaptations.
•Acute aerobic exercise results in
-Increased cardiac output -Increased stroke volume -Increased heart rate -Increased oxygen uptake -Increased systolic blood pressure -Increased blood flow to active muscles -Decreased diastolic blood pressure
Chronic Adaptations to Aerobic Exercise: Cardiovascular adaptations
-Increases in maximal cardiac output, stroke volume, and fiber capillary density -Increased parasympathetic tone leads to decreases in resting and submaximal exercise heart rates
External and Individual Factors Influencing Adaptations to Aerobic Endurance Training: age and sex
-Maximal aerobic power decreases with age in adults. -Aerobic power values of women range from 73% to 85% of the values of men. -The general physiological response to training is similar in men and women.
Chronic Adaptations to Aerobic Exercise: Muscular adaptations
-One of the fundamental adaptive responses to aerobic endurance training is an increase in the aerobic capacity of the trained musculature. -This adaptation allows the athlete to perform a given absolute intensity of exercise with greater ease after aerobic endurance training.
Endocrine responses to overtraining
-Overtraining may result in a decreased testosterone-to-cortisol ratio, decreased secretion of GH, and changes in catecholamine levels.
Aerobic endurance training results in
-Reduced body fat -Increased maximal oxygen uptake -Increased running economy -Increased respiratory capacity -Lower blood lactate concentrations at submaximal exercise -Increased mitochondrial and capillary densities -Improved enzyme activity
•Tapering
-The planned reduction of volume in training that occurs before an athletic competition or a planned recovery microcycle.
Chronic Adaptations to Aerobic Exercise: Respiratory adaptations
-Ventilatory adaptations are highly specific to activities that involve the type of exercise used in training. -Training adaptations include increased tidal volume and breathing frequency with maximal exercise.
Diffusion
Diffusion is the movement of oxygen and carbon dioxide across a cell membrane and is a function of the concentration of each gas and the resulting partial pressure exerted by the molecular motion of each gas. Diffusion results from the movement of gas from high concentration to low concentration. The diffusing capacities of oxygen and, in particular, carbon dioxide increase dramatically with exercise, which facilitates their exchange.
Aerobic endurance training results in several changes in cardiovascular function, including increased maximal cardiac output, increased stroke volume, and reduced heart rate at rest and during submaximal exercise.
In addition, muscle fiber capillary density increases as a result of aerobic endurance training, supporting delivery of oxygen and removal of carbon dioxide. For optimal aerobic exercise performance, increasing maximal oxygen uptake is of paramount importance.
-Decreased performance -Decreased percentage of body fat -Decreased maximal oxygen uptake -Altered blood pressure -Increased muscle soreness -Decreased muscle glycogen -Altered resting heart rate
Some of the markers of aerobic overtraining
-Decreased ratio of total testosterone to sex hormone-binding globulin -Decreased sympathetic tone (decreased nocturnal and resting catecholamines) -Increased sympathetic stress response -Change in mood states -Decreased performance in psychomotor speed tests
Some of the markers of aerobic overtraining
-Increased submaximal exercise heart rate -Decreased lactate -Increased creatine kinase -Altered cortisol concentration -Decreased total testosterone concentration -Decreased ratio of total testosterone to cortisol -Decreased ratio of free testosterone to cortisol
Some of the markers of aerobic overtraining
•cardiac output (or Q):
The amount of blood pumped by the heart in liters per minute (SV × HR).
Maximal aerobic power decreases with age in adults as a consequence of various physiological changes that accompany aging—for example, reduced muscle mass and strength (also called sarcopenia) and increased fat mass.
The differences in aerobic power in men and women may be caused by several factors, including women's higher percentage of body fat and lower blood hemoglobin values and men's larger heart size and blood volume.
•stroke volume:
The quantity of blood ejected with each beat.
After training, an athlete can exercise at a greater relative intensity of a now-higher maximal aerobic power. The muscular component of an aerobic endurance training program involves submaximal muscle contractions extended over a large number of repetitions with little recovery. Therefore, the relative intensity is very low, and the overall volume is very high.
This manner of training encourages relative increases in aerobic potential that are similar in Type I and Type II fibers.
primary mechanisms for regulating regional blood flow.
Vasoconstriction and vasodilation of blood vessels
•One of the most commonly measured adaptations to aerobic endurance training is
an increase in maximal oxygen uptake associated with an increase in maximal cardiac output.
Most adaptations in maximal oxygen consumption can be achieved within
a 6-to 12-month training period.
Ventilation generally does not limit aerobic exercise and is either unaffected or only moderately affected by training. Furthermore, the ventilatory adaptations observed appear to be highly specific to activities that involve the type of exercise used in training; that is,
adaptations observed during lower extremity exercise primarily occur as a result of lower extremity training. If exercise training focuses on the lower extremities, one will not likely observe ventilatory adaptation during upper extremity activities.
•Proper exercise variation, intensity, maintenance programs, and active recovery periods can
adequately protect against serious detraining effects.
Unusually high training volume can result in increased levels of creatine kinase (CK), indicating muscle damage. Lactate concentrations, on the other hand, either
decrease or stay the same when training volumes increase.
Compared to Type II fibers, Type I fibers
have a higher preexisting initial aerobic capacity, to which the increase in aerobic potential from training is added. Thus, Type I fibers possess an oxidative capacity greater than that of Type II fibers both before and after training.
Endocrine responses to overtraining stimulus appear to be due to
impaired hypothalamic function, not pituitary function. Whether these endocrine alterations are responsible for performance decrements is open to debate.
Increased training volumes, within a given time period, associated with overtraining do not generally affect resting blood pressures. However, increased training intensity can produce
increased resting diastolic blood pressures without affecting resting systolic pressures.
Overtraining syndrome can lead to dramatic performance decreases in all athletes; the most common cause is intensified training without adequate recovery.
intensified training without adequate recovery.
•Overtraining syndrome can lead to dramatic performance decreases in all athletes; the most common cause is
intensified training without adequate recovery.
As the intensity of exercise increases, oxygen consumption rises to maximal levels. When oxygen consumption can no longer increase to meet the demands,
maximal oxygen uptake has been achieved even in the presence of continuing oxygen availability. Aerobic endurance training can improve an athlete's aerobic power by 5% to 30%, depending, in part, on the starting fitness level as well as the genetic potential of the individual.
•During aerobic exercise, large amounts of oxygen diffuse from the capillaries into the tissues; increased levels of carbon dioxide move from the blood into the alveoli; and
minute ventilation increases to maintain appropriate alveolar concentrations of these gases.
The intensity of training is
one of the most important factors in improving and main-taining aerobic power.
Normal resting blood pressure generally ranges from 110 to 139 mmHg systolic and from 60 to 89 mmHg diastolic. With maximal aerobic exercise,
systolic pressure can normally rise to as much as 220 to 260 mmHg, while diastolic pressure remains at the resting level or decreases slightly.
Neural adaptations- improved aerobic performance may result in a rotation of neural activity among synergists (i.e., rather than maintaining a constant state of activation, synergistic muscles alternate between active and inactive to maintain low-level muscular force production ) and among motor units within a muscle. Thus,
the athlete produces more efficient locomotion during the activity with lower energy expenditure
With aerobic exercise, increased minute ventilation occurs as a result of increases in
the depth of breathing, frequency of breathing, or both.
During strenuous exercise, the breathing frequency of healthy young adults usually increases from 12 to 15 breaths per minute at rest to 35 to 45 breaths per minute, while tidal volume, (the amount of air inhaled and exhaled with each breath), increases from resting values (of 0.4 to 1 L) to as much as 3 L or greater. Consequently,
the minute ventilation can increase to 15 to 25 times the resting value, or to values of 90 to 150 L of air per minute
The primary functions of the cardiovascular system during aerobic exercise are to deliver oxygen and other nutrients to the working muscles and remove metabolites and waste products. Stroke volume begins to increase at
the onset of exercise and continues to rise until the individual's oxygen consumption is at approximately 40% to 50% of maximal oxygen uptake. At that point, stroke volume begins to plateau.
Minute ventilation
the volume of air breathed per minute
Acute Responses to Aerobic Exercise: Control of local circulation
•During aerobic exercise, blood flow to active muscles is considerably increased by the dilation of local arterioles. •At the same time, blood flow to other organ systems is reduced by constriction of the arterioles.
Acute Responses to Aerobic Exercise: Respiratory gas responses
•During high-intensity aerobic exercise, the pressure gradients of oxygen and carbon dioxide cause the movement of gases across cell membranes. •The diffusing capacities of oxygen and carbon dioxide increase dramatically with exercise, which facilitates their exchange.
Acute Responses to Aerobic Exercise: -Stroke volume
•End-diastolic volume is significantly increased. •At onset of exercise, sympathetic stimulation increases stroke volume.
resting oxygen uptake:
•Estimated at 3.5 ml of oxygen per kilogram of body weight per minute (ml·kg-1·min-1); this value is defined as 1 metabolic equivalent (MET).
Acute Responses to Aerobic Exercise: Cardiac Output
•From rest to steady-state aerobic exercise, cardiac output initially increases rapidly, then more gradually, and subsequently reaches a plateau. With maximal exercise, cardiac output may increase to four times the resting level
O2 and CO2 in blood:
•Most oxygen in blood is carried by hemoglobin. •Most carbon dioxide removal is from its combination with water and delivery to the lungs in the form of bicarbonate.
Acute Responses to Aerobic Exercise: Blood pressure
•Systolic blood pressure estimates the pressure exerted against the arterial walls as blood is forcefully ejected during ventricular contraction. •Diastolic blood pressure is used to estimate the pressure exerted against the arterial walls when no blood is being forcefully ejected through the vessels.
•During low- to moderate-intensity aerobic exercise, enough oxygen is available that lactic acid does not accumulate because the removal rate is greater than or equal to the production rate.
•The aerobic exercise level at which lactic acid (converted to blood lactate at this point) begins to show an increase is termed the onset of blood lactate accumulation, or OBLA. (Acute response to aerobic exercise)
maximal oxygen uptake
•The greatest amount of oxygen that can be used at the cellular level for the entire body.