Week 09 Flashcards
Skeletal muscle “motor” of children and adults works at about 20% efficiency, this means that during exercise ____ times as much energy generates heat as produces locomotion
four
Radiation:
heat loss through rays or waves of energy
Conduction:
losing heat through physical contact
Convection:
losing heat through air or water molecules (fan)
Evaporation:
losing heat through conversion of water to gas
Dehydration can cause a rise in ?????
Core body temperature
Sweating rate in boys is _____ than in men
Much lower
Due to lower sweating rate in boys, they rely more on increased ??????? for convective skin heat loss than men
cutaneous blood flow
Men sweat ____ more than women
3x
Is there a difference in girls vs women’s sweat rate?
Some studies show no differences, however, conflicting evidence
The number of sweat glands increase or is fixed at infancy?
Fixed at infancy, doesn’t increase
Children have _____ surface area relative to their body mass
greater
Because of their relatively greater body surface area, children have more effective heat loss via _____ than adults
convection
Responses to Exercise in the Heat: cardiovascular drift
- increase body temp
- increase BF to skin
- Shift of fluid from vascular space
- less ventricular filling
- stroke volume smaller
- smaller CO
- compensate with increase in HR
- called cardiovascular drift
In the heat, children sweat less than adults and must rely upon diminishingly effective _____ loss to prevent a rise in core temp
convective
Children’s greater body surface area relative to body mass also becomes a liability when the…
skin-to-air temperature gradient is reversed
Concentration of sodium in sweat tends to be _____ in children
lower
Given the lower sweating rates in young subjects (at least among males), total sodium losses through sweating can be expected to be ____ in children
less
Children generate ____ heat relative to body mass than adults when performing the same task
more
The number of sweat glands ______ during puberty
stays the same
- We would expect children to demonstrate an exaggerated rise in core temp at high ambient temp
- However, experimental data suggests ____ changes in core temp between children and adults under hot conditions
similar
It is more common for ____ to experience symptoms of fatigue when air temperature is greater than skin temperature by over 10 degrees C (47C)
children
Drinkwater et al performed walking tests in hot temperatures among women and girls and found….
Women performed these walks for longer and could deal with temperatures better–> heat tolerance is better in adults.
What are the potential factors responsible for exercise fatigue in the heat in adults?
- Cardiovascular insufficiency from the shunting of blood volume to cutaneous circulation for convective cooling
- Dehydration and depressed blood circulation from fluid losses as sweat
- Metabolic or substrate alterations
- Impairment of myocardial contractility
Traditional explanation for exercise intolerance in heat is shunting of blood to cutaneous circulation and away from working muscles.
However, evidence suggests ….?
muscle blood flow is not limited in the heat.
Is blood flow to muscle responsible for lack of exercise performance in the heat?
No
Dehydration caused by significant sweating may diminish left ventricular filling and thereby decrease SV, however, studies indicate only small reductions in ____
CO
Was there a reduction in CO observed in dehydration or hyperthermia?
No, only reduction in CO when they had BOTH
Optimal muscle temperature range for force production: _______degrees C
30-37C
Febbraio found that metabolic consequences (Ca+ uptake, reduced integrity of membranes) only occurred when muscle temp reached ….?
40 degrees C
Nielsen et al reported no effects of exercise in the heat on ????????? of elbow flexors and knee extensors
muscular strength
Once core temperatures exceed 40 degrees C, evidence suggests deterioration of ___ _____ capacity
heart pumping
Data in adults fail to identify a single factor that clearly explains limitations of exercise performance in the heat.—-> as…
- CO has fallen little
- Muscle blood flow has not decreased
- Muscle glycogen stores are adequate
- Muscle contractile force is not affected
- Myocardial contractility is preserved
Nielsen et al suggested that “the high core temp per se, and not _____ _____, is the critical factor for exhaustion during exercise in heat stress”
circulatory failure
Core temp of >__C may reduce the function of motor centres and the ability to recruit motor units. However, evidence is limited
39C
Jokinen et al. studied cardiovascular adjustments to 10 min of sauna heat, symptoms only evident in ____ age group:
young, 25% complained of “dizziness and feeling too hot”
Jokinen et al. found that there was a greater fall in ___ in the youngest children and greater rise in ____
SV, core body temp
Rowland et al found no difference in SV, however, in girls vs women in heat exercise, this may be due to…?
They had fluids to replenish fluid loss, and temperature was not as hot as Jokinen et al study.
Lower tolerance of heat in ____ than in ____, primarily due to…?
girls, women…. due to cardiovascular problem
These limited data suggest that children tolerate exercise in the heat as well as adults except in….?
Very high ambient temperatures
Is there compelling evidence that cardiovascular insufficiency is responsible for possible differences in performance in the heat between children and adults ??
No
Drinking ad libitum (desired amount) generally only replaces up to ____% of the fluid lost
70%
- Limited evidence suggests that the magnitude of involuntary dehydration in children is ____ to that of adults.
Similar
___% of adult weight gained during growth spurt
50%
Physically active boys did/did not differ in stature or age of peak height velocity compared to sedentary boys
did not
Male testosterone levels are x___ after puberty
20
