heat

• thermoregulation - process of maintaining internal core temperature
• thermoreceptors - sensory receptors which sense a change in temperature and relay information to the brain
• dehydration - loss of water in body tissues, largely caused by sweating
• thermoregulation - maintaining internal core temperature

  • human body temperature = 37 degrees
  • thermoreceptors; detect changes in temperature
  • if core temperature rises, metabolic heat is transported by the circulating blood to the surface of the body & released by convection and evaporation (sweat)
  • athletes exercising in the heat can lose 2-3 litres per hour
  • if fluid is not replaced, blood volume decreases and causes dehydration, which impairs the ability of the body to thermoregulate and core temperature will rise
• humidity - the amount of water in the atmospheric air
• low humidity - increases sweating
• high humidity - decreases sweating
• hyperthermia - significantly raised core body temperature
• causes of hyperthermia:

  • high and prolonged exercise intensities
  • high air temperatures
  • high relative humidity
• cardiovascular drift - upward drift of heart rate during sustained steady state activity associated with a rise in body temperature due to hot environments
• cardiovascular drift:

  • redirection of blood flow to the skin for cooling this limits blood flows to the muscle and venous return
  • rise in core temperature alters the function of protein molecules e.g enzymes and receptors and affects the rate of chemical reactions
• effect of heat, humidity and body's response of cardiovascular system:

  • dilation of arterioles and capillaries to the skin, leading to;

  -increased blood flow and blood pooling at the limbs

  • decreased blood volume, venous return, stroke volume, cardiac output and blood pressure, leading to;

  -increased heart rate to compensate

  -increased strain on cardiovascular system

  -reduces oxygen transport to the working muscles
• effect of heat & humidity on the respiratory system:

  • dehydration & drying of the airways in temperatures above 32 degrees making breathing difficult leading to;

  -increased mucus production

  -constriction of airways

  -decreased volume of air for gaseous exchange

  • increased breathing frequency to maintain oxygen consumption leading to; increased oxygen cost of exercise
  • high levels of sunlight increase the effect of pollutants in the air, causing; increased irritation of airways, leading to coughing, wheezing or asthma symptoms
• overall effect of heat on CV and RS:

  • increased oxygen cost of activity and decreased aerobic energy production
  • shifts emphasis to anaerobic energy production using carbohydrate stores more quickly
  • exercise duration decreases due to lactic acid accumulating more readily, leading to early fatigue
  • strength endurance and aerobic capacity reduced, declining performance in mid to long distance events
  • athletes with exercise induced asthma must take precautions
• heat effect on performer:

  • at higher temperatures, perceived exertion will feel higher for the performer
  • strength and endurance based activities are affected differently due to the different intensity duration and opportunity for fluid intake
  • hyperthermia does not affect maximal strength production - explosive and maximal events unaffected
  • the longer the event, the greater the effect on performance
  • the more elite the endurance athletes, the lower impact the impact of heat due to physiological adaptations, precaution taken and acclimitisation.
• Precaution procedures: Pre-competition

  • Acclimatise to increased temperatures. 7-14 days of

  acclimatisation increases the body’s tolerance to heat by:

  -Increasing plasma volume, the onset and rate of sweating, and the

  efficiency of cardiac output distribution

  -Decreasing the loss of electrolytes within the sweat, which limits

  fatigue and cramping

  -Decreasing heart rate at a given pace and temperature

  • Use cooling aids such as ice vests to reduce core temperature and

  delay the effect of high temperatures and dehydration
• Precaution Procedures: During Competition

  • Use pacing strategies to alter goals and reduce feelings of exertion at low-exercise intensities
  • Wear suitable clothing that maximises heat loss, removing sweat from skin rapidly, such as lightweight compression wear
  • Rehydrate as much as possible with a hypotonic or isotonic solution that replaces primarily lost fluids but also glucose and the electrolytes lost through sweat.
• Precaution Procedure: Post Competition

  • Cooling aids, such as cold towels and cold fans, aid the return of core body temperature gradually
  • Rehydrate using isotonic solutions that replace lost fluids, glucose and electrolytes