W5 - Exercise in the Heat Flashcards
What issues do athletes face when doing vigorous exercise in the heat?
- Generating metabolic heat in exercise
- Heat not being released properly
- Temperature can only go up so far
- He is hypo hydrated - dehydrated –> sweating as much as possible to release heat
- Blood is not going to the muscles, heart where it is needed - going to the skin instead to decrease body temperature
- Carbohydrate stores are depleted even faster in heat(can come through liver/ingesting food)
How is body temperature regulated?
Body temperature is maintained within a narrow range
– Humans are homeothermic
* In extreme cases, body temperature will deviate from the normal range (36.1-37.8°C)
– E.g. heavy exercise, fever from illness and extreme hot or cold conditions
What are the main 2 ways a person loses heat in exercise?
Convection - is mainly wind flow, air flow, more convection in water than air
Evaporation - sweat evaporating off of the skin
What do we measure in heat balance?
Core temperature – Tc
* Skin temperature – Tsk
* Whole body sweat rate
* Local sweat rate
* HR
* VO2/ VCO2
* Plasma volume changes
* Performance
* Thermal comfort
* RPE
* Blood flow
Describe the thermoregulatory control that takes place in the body
Internal body temperature is closely regulated
* Regulated by the preoptic-anterior hypothalamus
* Thermoreceptors detect changes in temperature
* Signals through the sympathetic nervous system:
- Vasodilation of blood vessels
- Increased activation of sweat glands
Explain the physiological responses an athlete has to exercising in the heat
Cardiovascular function
– Skin arterioles vasodilate ↑ skin blood flow
– ↑ Cardiac output
– ↓ Stroke volume (sweat) –> ↑ HR (CV drift)
– Heart cannot provide sufficient blood flow to heart and skin
– ↓ Performance
* ↑Sweating –> ↓ Blood volume –> ↓Cardiac output
What equipment do we use to determine heat stress?
Wet bulb globe thermometer: typically used in the lab
Which type of athletes are most effected by high heat?
long or short distance?
Short distance: there is no prolonged exposure to the heat
- Not effected by substrate delivery, evaporation
- Marathon is the most effected
How does fluid intake help to deal with the heat?
- Fluid intake maintains or reduces the decrease in plasma volume arising from fluid lost as sweat
– Helps maintain stroke volume and cardiac output
– Therefore maintain or prevent reduction in performance
What are some cooling strategies that are used?
- Ice baths - targeting main arteries
- Iced drinks
- Ice vests
What is heat acclamation?
What is heat acclimatisation?
- Heat acclimation - the physiological changes that occur over a short period of time
- Heat acclimatisation - physiological changes as a result of living in a hot climate for months/years
- By performing a period of heat acclimation athletes can develop beneficial physiological changes and adaptations that may help maintain/prevent reductions in performance
- Heat acclimation period can vary in duration, methods and intensity
- Often performed before competitions/military
When does exercise in the heat go wrong?
During exercise core temperature will rise
* In extreme conditions it will continue to rise despite the compensatory mechanisms
– Heat
– Humidity
– High intensity exercise
* In severe cases exertional heatstroke (EHS) occurs (>40.5°C) – can ultimately lead to death if not treated correctly
* Measuring heat stress can assess the conditions
What are some practical considerations for exercising in the heat?
- Consider cancellation when WBGT >28°C
- Ensure adequate fluid intake
- Practice early morning or late evening
- Factor in breaks in play
- Minimise amount of clothing worn
- Ensure coaches and athletes are aware of EHS
- A period of heat acclimation
