Athletic Performance Nutrition Exam #3 Flashcards
Mechanisms for Temperature Regulation: stimulated by heat
- Increases heat loss ->
vasodilation of subcutaneous skin vessels; sweating - Decreases heat production -> decreased muscle tone & voluntary activity; decreased thyroxine & epinephrine secretion
Mechanisms for Temperature Regulation: stimulated by cold
- Decreases heat loss -> Vasoconstriction of skin vessels; postural reduction of surface area (curling up)
- Increases heat production -> Shivering and increased voluntary activity; increased thyroxine and epinephrine secretion
How does the body primarily protect itself from overheating
Using the body’s thermoregulatory mechanisms
Deep tissue or core body temp represents a dynamic equilibrium between factors that add & subtract body heat. What are the 3 integrating mechanisms that thermal balance results from?
- Alter heat transfer to the periphery or shell
- Regulate evaporative cooling
- Vary heat production rate
During sustained PA for aerobically fit men & women, metabolism often increases to how much above resting level?
20-25x above resting level or 20kcal/min
What will heat production of this magnitude theoretically increase core temperature by?
1 degree Celsius every 5 to 7 minutes
What does the hypothalamus contain?
The central neural coordinating center for temperature regulation
What are the 4 ways the body loses heat?
- Radiation
- Conduction
- Convection
- Evaporation
Do objects continually emit electromagnetic heat waves?
Yes
How does the body transfer heat directly using conduction?
Through liquid, solid, or gas from one molecule to another
What does this group of specialized neurons at the floor of the brains serve as?
“Thermostat” (usually set & carefully regulated at 37 degrees Celsius +or- 1 degree; 98.6 degrees Fahrenheit +or- 1.8 degreees
What does the rate of conductive heat loss depend on?
It depends on a temperature gradient between the skin and surrounding surfaces and their thermal qualities
What 2 ways cause heat-regulating mechanisms to become activated?
- Temp changes in blood perfusing the hypothalamus directly stimulate this thermoregulatory control center
- Thermal receptors in the skin provide input to modulate hypothalamic activity
When does sweating start during vigorous activity?
Sweating begins within several seconds
What occurs with sweat after 30 mins of vigorous activity?
Sweating reaches an equilibrium directly related to exercise load
What does the effectiveness of of heat loss by conduction via air depend on?
How rapidly air near the body exchanges once it warms
How many sweat or eccrine glands are there?
2-4 million
What does evaporation of sweat provide?
The major physiological mechanism for heat loss & thus defense against overheating
What does the posterior pituitary gland do during heat exposure?
It recreates antidiuretic hormone (ADH), which increases water reabsorption from the kidney tubules to create more concentrated urine
What does hot weather stimulate?
It stimulates the adrenal cortex to release the sodium-conserving hormone aldosterone, which increases sodium reabsorption by the renal tubes
What do sweat glands secrete in large quantities in response to heat stress?
Hypotonic saline solution (0.2 to 0.4% NaCl)
How many ml of water seeps through the skin each day and evaporates to the environment?
350ml
What are the 5 factors other than air temperature that determine heat-imposed physiologic strain?
- Body size and fatness
- Level of training
- Acclimatization
- Adequacy of hydration
- External factors (convective air currents; radiant heat gains; intensity of activity; amount, type, and colour of clothing; and most importantly, relative humidity)
What is water seeping through the skin called?
Insensible persperation
How many ml of water vaporizes daily from the respiratory passages moist mucous membranes?
300 ml of water
What 3 factors determine sweat evaporation from skin?
- Surface area exposed to the environment
- Ambient air temp & relative humidity
- Convective air currents around the body
Does relative humidity exert the greatest impact on the effectiveness of evaporative heat loss?
Yes, by far
What is the most effective way to minimize or eliminate heat stress injuries?
Prevention
Does large sweat output and subsequent fluid loss occur in sports other than distance running?
Yes, football, basketball, and hockey players also lose large quantities of fluid during practice or competitions
What is relative humidity?
The percentage of water in ambient air at a particular temperature compared to the total quantity of moisture the air could carry (ex: 40% humidity means ambient air contains only 40% of air’s moisture-carrying capacity at specific temp)
Does sweat cool the skin or does skin cooling occur only when sweat evaporates?
Skin cooling occurs only when sweat evaporates
Does continually drying the skin with a towel before sweat evaporates also thwart evaporative cooling?
Yes
Does the circulatory system serve as the main “workhorse” to control thermal balance?
Yes
With extreme heat stress, 15-25% of the cardiac output passes through the skin, greatly increasing the thermal conductance of peripheral tissues. T/F
True
Can heat generated by active muscles raise core temperature to fever levels that incapacitate a person if caused by external heat stress alone?
Yes
What 5 changes in body function coincides with the body fluid loss?
- Decreased plasma volume
- Reduced skin blood flow for a given core temperature
- Reduced stroke volume of the heart
- Increased HR
- General deterioration in circulatory and thermoregulatory efficiency during physical activity
More than likely, will a modest rise in core temp reflect a favorable internal adjustment that will create an optimal thermal environment for physiologic & metabolic functions?
Yes
What is dehydration?
An imbalance in fluid dynamics when fluid intake doesn’t replenish water loss from either hyperhydrated or normally hydrated states.
How much sweat loss occurs over a 1-hour period during moderate PA?
0.5-1.5 L sweat loss
Does dehydration correlate with 3% decrease in body weight, which slows gastric emptying rates, thus triggering of epigastric cramps & nausea?
Yes
Does adequate fluid replacement sustains evaporative cooling of acclimatized humans? Properly scheduling fluid replacement maintains plasma volume so circulation seating progress? - T/F
True
Sweat is hypotonic with other body fluids, so reduced plasma volume caused by sweating correspondingly increases blood plasma osmolality T/F
True
Intracellular & extracellular compartments contribute to any fluid deficit (dehydration) that can reach levels that impede heat dissipation, reduce heat tolerance, & severely compromise cardiovascular function & exercise capacity. The risk of heat Illness increases greatly when a person begins activity in a dehydrated state. T/F
True
What does 1-pound weight loss represents?
450 mm of dehydration
Does the risk of heat illness increase greatly when a person begins activity in a dehydrated state?
Yes
What is the recommended fluid intake?
15 mins hourly loses up to 1000 mm, whereas fluid ingestion at 10 min intervals optimizes replenishing fluid loss in excess of 1000 mL per hr
When left on their own do most individuals voluntarily replace only about half of the water lost (<500ml/h) during PA?
Yes
How long would it take to reactive fluid balance if rehydration was left entirely to a person’s thirst?
Several days following severe dehydration to re-establish fluid balance.
Does a well-hydrated individual always function at a more optimal physiologic & performance level than a dehydrated one?
Yes
What are “cold treatments”?
Periodic application of cold towels to the forehead & abdomen during PA, or taking a cold shower before exercising in a hot environment.
What three beverages do boys voluntarily consume after physical activity, dehydration, and heat exposure?
- Plain water
- Grape-flavoured water
- Grape-flavoured water containing 6% carbohydrate
How much water should be drunk to compensate for water lost during activity?
Enough liquid to equal at least 125 to 150% of the amount of body weight lost during physical activity. The 25 to 50% “extra” water accounts for that portion of ingested water lost in urine
Does ingesting “extra” water (hyperhydration) before PA in a hot environment protect against heat stress?
Yes
What 3 effects does hyperhydration foster?
- Delays dehydration
- Increases sweating during PA
- Minimizes core temp increase
Do these 3 hyperhydration effects enhance performance & overall safety?
Yes
What are recommendations for consuming water 24 hours before PA in heat and 20 minutes before?
24hr: Increase fluid intake
20min: 400-600ml of cool water
Do “cold treatments” facilitate heat transfer at the body’s surface when compared with the same PA without skin wetting?
No
In intense endurance activities in the heat, matching fluid loss with fluid intake often becomes impossible, because only about 1000ml of fluid each hour empties from the stomach. T/F
True
Do body weight changes indicate the extent of water loss from PA & adequacy of rehydration during & after activity of athletic competition?
Yes
What does voiding small volumes of dark yellow urine with a strong odor indicate?
A qualitative indication of inadequate hydration (well-hydrated individuals produce urine in large volumes, light in color, & w/out noticeable smell)
What provides the most effective defense against heat stress by balancing water loss with water intake rather than by pouring water over the head/body?
Adequate hydration
Does a moderate amount of sodium added to a rehydration beverage provide more complete rehydration after PA & thermal-induced dehydration than plain water?
Yes
When does restoring water & electrolyte balance in recovery occur most effectively?
By adding moderate to high amounts of sodium to the rehydration drink (100 moles/L, an amt exceeding commercial drinks) or by combining solid food with appropriate sodium content & plain water
With the kidneys continually forming urine should ingested fluid volume following PA exceed sweat loss by 25-50% to restore fluid?
Yes
Can some individuals produce relatively highly concentrated sweat regardless of their degree of acclimatization?
Yes
What does the development of hyponatremia require?
Extreme sodium loss through prolonged sweating coupled with dilution of existing extracellular sodium and accompanying reduced osmolarity form consuming large fluid volumes containing low or no sodium
What are the 4 factors that are a concern during hot-weather physical activity?
- Dehydration
- Decreased plasma volume and resulting hemoconcentration
- Impaired physical performance and thermoregulatory capacity
- Increased heat injury risk (especially heat stroke)
What happens with repeated exposure to hot environments combined with physical activity?
Improves exercise capacity with less discomfort upon heat exposure
What is heat acclimatization?
The physiologic adaptations that improve heat tolerance
What is the effect of the acclimatization response to improved cutaneous blood flow?
Transport metabolic heat from deep tissues to the body’s shell
What does Figure 10.10 show?
That major acclimatization to heat stress occurs during the first week of heat exposure (2-4 hr daily) with essentially complete acclimation after 10 days. In practical terms, use 15-20 mins of light-intensity physical activity during the first several sessions in a hot environment
What is the effect of the acclimatization response to effective distribution of cardiac output?
Appropriate circulation to skin and muscles to meet demands of metabolism and thermoregulation; greater stability of blood pressure during exercise
What is the effect of the acclimatization response to lowered threshold for start of sweating?
Evaporative cooling begins early during exercise
What is the effect of the acclimatization response to more effective distribution of sweat over skin surface?
Optimum use of effective surface for evaporative cooling
What is the effect of the acclimatization response to increased sweat output?
Maximizes evaporative cooling
What is the effect of the acclimatization response to lowered salt concentration in sweat?
Frees greater portion of cardiac output for distribution to active muscles
What is the effect of the acclimatization response to less reliance on carb catabolism during exercise?
Carb-sparing effect
Does colour play an important role in radiant heat gain?
Yes; dark colours absorb more heat as light rays (energy) and add to radiant heat gain
Do football uniforms and equipment present a considerable barrier to heat dissipation during environmental heat exposure?
Yes; even though loose-fitting porous jerseys, wrappings, padding (with plastic covering), helmets, and other objects of “armour” effectively seal off 50% of the body’s surface from the benefits of evaporative cooling
From a practical standpoint, should children exposed to environmental heat stress exercise at reduced intensity & devote more time to acclimatizing than more mature competitors?
Yes
Do Prepubescent children have more heat-activated sweat glands per unit skin area than adolescents and adults, yet sweat less & achieve higher core temperatures during heat stress?
Yes
What is Ergogenic (work producing)?
Refers to application of nutritional, physical, mechanical, psychological, physiologic, and pharmacologic procedures or aids to improve physical capacity athletic performance, and responsiveness to training
Generally women tolerate the physiological & thermal stress of PA as well as men of comparable fitness & level of acclimatization; both sexes acclimatize to a similar degree. T/F
True
Women rely more on circulatory mechanisms for heat dissipation, whereas greater evaporative cooling occurs in men. T/F
True
Does excess body fat negatively influence performance in hot environments?
Yes
Women possess more heat-activated sweat glands per unit skin area than men, yet they sweat less prolifically. Women begin sweating at higher skin & core temperatures; they also produce less sweat for a similar heat-activity load, even with acclimatization comparable with that of men. T/F
True
Do children also take longer to acclimatize to heat than adolescents & young adults?
Yes
Does the indiscriminate use of alleged ergogenic substances increase the likelihood of adverse effects that range from relatively benign physical discomfort to life-threatening episodes?
Yes
During the 15th century, athletes of the Victorian era routinely used caffeine, alcohol, nitroglycerine, heroin, cocaine, & other stimulants to gain a competitive edge. T/F
True
Athletes of Ancient Greece from about 700-3000 B.C. Reportedly used hallucinogenic mushrooms, plant seeds, & ground dog testicles for ergogenic purposes, while Roman gladiator athletes ingested the equivalent of “speed” to enhance performance in the Circus Maximus. T/F
True
What does the term ‘functional food’ mean?
An increasing belief in the potential for selected foods to promote health
Why are ergogenic aids complex & controversial and why is there a heightened interest in them?
People want to win
What is the process of randomization in research?
When subjects volunteer for an experiment, they must be randomly assigned to either a control or experimental condition