Sports nutrition, ch. 10

Relative humidity refers to the-

% of water in ambient air at a particular temperature compared with the total quantity of moisture the air could carry

ACSM recommends that sports drinks contain how much sodium per liter of fluid consumed during exercise lasting more than one hour?

.5 to .7 g

A moderate exercise workout generally produces what amount of sweat loss over a 1 hr period?

.5-1.5 L

Body fluid loss coincides with the following five changes in bodily functions:

1. Decreased plasma volume 2. Reduced skin blood flow for a given core temp 3. Reduced stroke volume of the heart 4. Increased heart rate 5. General deterioration in circulatory and thermoregulatory efficiency in exercise

Ingesting extra water (hyperhydration) before exercise in a hot environment protects to some extent against heat stress because it fosters these three effects-

1. Delays dehydration 2. Increases sweating during exercise 3. Diminishes the rise in core temp

Individual differences in accommodation and a limitation depend on the following six factors-

1. Genetic characters 2. Available resources 3. Age 4. Nature and duration of previous experience s 5. Number of similar previous experiences 6. Emotional and psychological response

The most prevalent factors associated with this disorder include-

1. Substantial pre-post race weight gain 2. Consumption of more than 3L of fluid during race 3. Race time greater than 4 hrs 4. Low body mass index

Three factors determine sweat evaporation from the skin:

1. Surface area exposed to the environment 2. Temperature and relative humidity of ambient air 3. Convection air currents around the body

Take these five steps to reduce risk of overhydration and hyponatremia in prolonged exercise-

1. Two to three hours before exercise drink 400-600 mL of fluid 2. Drink 150 to 300 mL of fluid about 30 minutes before exercise 3. Drink no more than 1000 mL•h of plain water spread over 15 minute intervals during or after exercise 4. Add a small amount of sodium to ingested fluid 5. Do not restrict salt

A person can tolerate a drop in deep body temperature of ____ degrees Celsius but an increase of only ____ degrees Celsius

10 5

Hyperthermia occurred more than

100 times over the past 30 years among football players who died from excessive heat stress.

With prolonged exercise in the heat, sweat loss depletes the body of how many grams of salt?

13-17 g about 8 g more than typically consumed in the diet.

Evaporative cooling under optimal conditions accounts for a heat loss of about-

18 kcal•min

Dehydration of only ___% body mass impairs physical work capacity and physiologic function and predisposes to _______ ________ when exercising in a hot environment.

2 Heat injury

During exercise in the heat, the strong drive for thermal balance can increase sweat rate to as high as-

3.5 L•h

In addition to increasing fluid intake 24 hrs before strenuous exercise in the heat we recommend consuming how much water about 20 minutes prior to exercise?

400-600 mL

Each liter of vaporized water transfers how many calories of heat energy from the body to the environment?

580

Most individuals acclimatize to virtually all of the earths stressful environments in about how many days of exposure?

8-14

Sweating begins within several seconds of the start of vigorous exercise. After about 30 minutes sweating reaches-

Equilibrium directly related to exercise load.

A small amount of potassium enhances water retention in the intracellularspace and may diminish -

Extra potassium loss that results from sodium retention by the kidneys.

Cutaneous and muscle blood volume increase during exercise in the heat, whereas the blood supply of other tissues is temporarily compromised. True or false

False

Indequate water replenishment not only impairs exercise capacity but also creates life threatening disturbances in-

Fluid balance and core temp

Glycogen depletion during exercise impairs high intensity endurance performance, yet failure to replenish this energy reserve does not impose a risk to-

Health and safety

Intercellular and extra cellular compartments contribute to the fluid deficit that can rapidly reach levels that impede-

Heat dissipation, reduce heat tolerance, and severely compromise cardiovascular function and exercise capacity.

Core temperature rises quickly when-

Heat gain exceeds heat loss as occurs during vigorous exercise in a warm environment.

The hypothalamus cannot turn off the heat. It can only initiate responses to protect the body from-

Heat gain or heat loss

The effectiveness of heat loss by conduction via air depends on-

How rapidly air near the body exchanges once it warms. Warmed air next to the skin acts as a zone of insulation

In response to heat stress, 2-4 million sweat glands secrete large quantities of-

Hypotonic saline solution. Cooling occurs when sweat evaporates from skin surfaces.

Dehydration-

Imbalance in fluid dynamics when fluid intake does not replenish water loss from either hyper hydration or normally hydrated states

What reduces the effectiveness of heat loss by conduction, convection, and radiation?

Increased ambient temperature. When ambient temperature exceeds body temperature these three thermal transfer mechanisms actually contribute to heat gain.

The process of maintaining internal stability termed by Bernard is-

Milieu interieur - the environment within. Represents the underlying principle of homeostasis

Heat exhaustion-

Most common among the physically active Develops in dehydrated, untrained, and unacclimatized people. First summer heat wave

The net exchange of radiant heat energy occurs from the body through the air to-

Nearby solid, cooler objects

Peripheral thermal receptors responsive to rapid changes in heat and cold exist predominantly as-

Nerve endings in the skin. The more numerous cutaneous cold receptors generally exist near the skin surface; and play an important role in initiating regulatory responses to cold environments.

Heat cramps-

Occur during or after intense physical activity, usually in the specific muscles exercised. Occurs because of dehydration and electrolytes

Evaporation of sweat provides the major physiologic mechanism for heat loss and thus defense against -

Overheating

The body's thermoregulatory mechanisms primarily protect against-

Overheating. Crucial during hot weather

A modest rise in core temperature reflects a favorable internal adjustment that creates an optimal thermal environment for-

Physiologic and metabolic functions

Heat loss occurs by the physical mechanism of -

Radiation, conduction, and convection.

Body heat loss occurs in four ways-

Radiation, conduction, convection, evaporation

Heat conservation occurs by-

Rapidly shunting blood deep to the cranial, thoracic, and abdominal cavities including portions of the muscle mass.

Heat stress initiates hormonal adjustments to conserve the loss of-

Salts and fluid in sweat

Thermal balance-

Shows body temperature of the deeper tissues or core in dynamic equilibrium between factors that add and subtract body heat.

Heat regulating mechanisms become activated in two ways:

Temperature changes in blood perfuming the hypothalamus directly stimulate this thermoregulatory control center. Thermal receptors in the skin provide input to modulate hypothalamic activity.

The circulatory system serves as the main workhorse to control-

Thermal balance pg. 324

Water loss due to diuretics triggers a disproportionate reduction in plasma volume, which negatively impacts -

Thermoregulation and cardiovascular function

heat illness-

Thirst, tiredness, grogginess, and visual disturbances pg. 340

Core temperature normally increases in exercise; the relative stress of exercise determines the magnitude of the increase. A well regulated temperature increase creates a more favorable environment for physiologic and metabolic functions. True or false.

True

What is the most important performance enhancing nutrient when exercise and heat stressors combine?

Water

Hyponatremia -

Water intoxication Ex sister when serum sodium concentration falls below 135; a serum sodium concentration below 125 triggers severe symptoms

During heat exposure the pituitary gland releases antidiuretic hormone (ADH) aka vasopressin. This is the hormone that increases-

Water reabsorption from the kidney tubules that causes urine to become more concentrated.

What's the most important avenue for heat loss?

Water vaporization or evaporation

In hot weather the adrenal cortex releases the sodium conserving hormone aldosterone-

Which increases the renal tubules reabsorption of sodium. Also decreases sodium concentration in sweat.

Women rely more on circulatory mechanisms for heat dissipation, whereas greater evaporative

cooling occurs in men

External heat stroke-

the most serious and complex heat stress malady, requires immediate medical attention.

Heat acclimatization refers to -

the physiologic adaptations that improve heat tolerance.

Five factors other than air temperature determine the physiologic strain imposed by heat-

1. Body size and fatness 2. Level of training 3. Acclimatization 4. Adequacy of hydration 5. External factors

The loss of acclimatization occurs in about how many days?

14-28

During sustained exercise by aerobically fit men and women metabolic rate often increases-

20-25x above the resting level to 20 kcal•min. Heat production by this magnitude could theoretically increase core temp by 1 degree Celsius every 5-7 minutes.

The kidneys continually form urine, so the volume of ingested fluid following exercise should exceed exercise sweat loss by -

25-50% to restore fluid balance.

How much does the metabolic rate increase from shivering?

3-5 fold

Heat loss by conduction transfers heat directly through-

A liquid, solid, or gas from one molecule to another. Most body heat goes to the periphery, but a small amount continuously moves by conduction directly trough deep tissues to the cooler surface.

Prepubescent children have a greater number of heat activated sweat glands per unit skin area than-

Adolescents and adults. They sweat less and achieve higher core temps

Thermal balance results from three integrated mechanisms-

Alter heat transfer to the periphery or she'll Regulate evaporative cooling Vary the rate of heat production

Which vitamins may need increases if you live in a hot environment?

B vitamins Vitamin c Vitamin b12

The hypothalamus contains the -

Central neural coordinating center for temperature regulation. The specialized neurons on the floor of the brain serves as a thermostat that makes thermoregulatory adjustments to deviations from a temperature norm.

Prolonged strenuous exercise in the heat changes -

Chromium, copper, iron, magnesium and zinc metabolism which often persists for several days into recovery.

The risk of dehydration increases during vigorous cold weather exercise because-

Colder air contains less moisture than air at warmer temperature, particularly at high altitudes. Consequently, greater fluid volumes leave respiratory passages as the incoming cold, dry air fully humidifies and warms the body temp

Several hours of intense sweating can cause sweat gland fatigue, which ultimately impairs -

Core temperature regulation

Four major factors are of concern in hot weather exercise-

Dehydration Decreased plasma volume and resulting hemp concentration Impaired physical performance and thermoregulatory capacity Increased risk of heat injury

Body weight changes indicate the extent of water loss from exercise and adequacy of rehydration-

During or after exercise or athletic competition

The cutaneous thermal receptors act as an-

Early warning system that relays sensory information to the hypothalamus and cerebral cortex.

Increased sweating strains fluid reserves, creating a relative state of dehydration. Excessive sweating without fluid replacement decreases plasma volume, and core temperature rises precipitously. True or false.

False

Women possess more heat activated sweat glands per unit skin area then men, yet they sweat -

Less prolifically Women begin sweating at higher skin and core temperatures

Heat index

Sometimes referred to as apparent temperature. It provides a measure of how hot it feels. Determined for shady and light wind conditions. Add up to 15 degrees Celsius for the sun

Maintaining a relatively high plasma concentration of sodium achieves three objectives-

Sustains the thirst drive Promotes retention of ingested fluids More rapidly restores lost plasma volume during rehydration

As exercise progresses and heat production increases, heat gain exceeds heat loss thereby initiating a -

Sweating response