Lecture 17 Flashcards
Heat Stress
major drivers for heat stress in exercise
exercise duration and intensity
normally the least important avenue for heat exchange in exercise is …
normally conduction is least important
the most important avenue for heat exchange in exercise is
evaporation
muscles can warm rapidly by how much ? during endurance and resistance exercise
2-3 degrees
what happens to the force and fatigue rate of hot muscles
WHY?
hot muscles can produce less force
and fatigue faster
increased glycogenolysis
what is the optimal temperature for swimming
around 27 degrees
what does exercise performance in the heat depend on
- exercise intensity
- clothing
- body composition
- body size
- exercise mode
what are two factors that lead to heat stress
exercise and environment
why does thermoregulation reduce exercise capacity
because you are having to thermoregulate and having to serve the metabolism of exercise
is thermoregulatory power finite
yes, it is limited by other effects of exercise on the body
when is heat stroke more likely to be fatal
when you were exercising
what temperature is the peak skin blood flow and sweat rate
38 degrees
temperature tolerance limit for moderately trained
39 degrees
temperature tolerance limit for many athletes, where increased cell permeabilities occurs
40 degrees
what temperature are some athletes able to tolerate
42 degrees
if no heat was dissipated what would the core temperature rise by in the body on active day
around 100 degrees
what is the main way our bodies gain heat
metabolism
other ways that our bodies gain heat
- radiation
- convection
- conduction
methods of heat loss
- evaporation (skin and respiratory)
- radiation
- convection
- conduction
what is heat production directly related to (equation)
work rate
heat production = metabolic rate - work rate
what does the capacity of environment to absorb heat depend on (5)
- water vapour pressure (absolute humidity)
- radiant temperature
- air movement (relative to the skin surface)
- resistance to heat transfer (clothing, posture)
- ambient temperature (dry bulb)
what is the most common way to represent the environmental effect in sport
Wet Bulb Globe Temperature (WBGT)
why are hot or humid environments stressful
harder to offload heat, especially if low evaporative capacity
what is the big picture of the physiological demands of exercise (where does blood flow need to be increased and what needs to be maintained)
- need increased muscle blood flow
- also need increase skin blood flow and sweating
- maintain arterial pressure
- adequate blood supply to other tissues
why does a warmer periphery occur in exercise in the heat
- increased skin blood flow and sweating
- increased blood osmolarity
why does blood osmolarity increase during exercise in the heat
because you sweat which causes loss of body water, so concentration of solutes in the blood increases
why is there a reduction in central blood volume during exercise in the heat
because there is a greater accumulation in the periphery
what happens to heart rate and stroke volume when exercising in the heat, to maintain cardiac output and mean arterial pressure
increased heart rate and decreased stroke volume
what happens to the amount of stress hormones when exercising in the heat
increase = have to activate the sympathetic nervous system more
what does offloading heat effectively require
requires evaporating water (sweat) off skin
what does dehydration cause in terms of heat loss and exercise tolerance
decreases both heat loss and exercise tolerance
what is evaporation for heat loss governed by and why
absolute humidity
- harder for sweat to evaporate from skin when the air surrounding is moist
