Thermoregulation Thermoregulation Homeostasis – Is the stable, constant temperature for the human body to most effectively function. This is around 37 degrees Celsius. Hypothermia – is the lowering of the core body temperature to such an extent that the body does not function normally. This is defined at 35 degrees celcius Hyperthermia – is the increase of the core body temperature to such an extent that the body does not function normally. This is defined at above 37.5 degrees Celsius. The body’s response to Hypothermia At rest or in extremely cold environments, the body may be in danger of hypothermia. To combat this the body increases heat production and decreases heat loss. This is done through: 1. Vasoconstriction – the narrowing of blood vessels to decrease flood flow. 2. Vascular adjustment – re-directing blood from the cooler surface to the warmer core. 3. Muscular activity – shivering is a involuntary response by the body to increase body temperature. The body’s response to Hyperthermia Radiation – by electromagnetic heat waves, the body gives off heat to surrounding (cooler) objects (no contact required) Conduction – is the transfer of heat from one object to another through contact. Convection – is the transfer of the body’s heat to the surrounding air (or water). Evaporation – Water/sweat vaporising from the body’s surface or respiratory passageway into the environment. Factors affecting heat tolerance Acclimatisation Training Status Age Gender Body Composition Acclimatisation The body needs time to adjust to warm environments Heat acclimatisation refers to the collective physiologic adaptive changes that improve heat tolerance. Generally, exercising in the first hot days in spring are the most difficult as the body is not as efficient yet, at dealing with the warmer environment Training Status Gains for the body’s ability to deal with heat improve after 8 -12 weeks of training at intensity above 50% aerobic capacity. This is due to body’s sensitivity to begin sweating at lower core temperatures and increase efficiency in blood flow Athletes who train and compete in hot weather have great thermoregulatory advantages over those who train in cooler weather. Age Children are less capable of cooling their body as they sweat less than adults. This may be due to underdeveloped peripheral mechanisms. Aged adults are less able to respond to the heat due to delayed onset of sweating and the altered structure of the skin Gender Controversy surround this issue with early studies indicating that men were better at tolerating exercise in the heat than women. However conflicting studies have since shown otherwise. It can be stated that only small differences surround men and women’s ability to function in the heat. Any differences include women’s decrease sweat rate and higher percentage of body fat. Body Composition Body fat acts as an insulator. This will keep heat in the body and cold out. Having increased body fat also results in higher weight to surface area, making it harder to cool the body. Reference Powers, S., K. and Howley, E., T., (2007). Exercise Physiology: Theory and application to fitness and performance, sixth edition. McGraw Hill, New York McArdle, W. D., Katch, F. I. and Katch V. L., (2007). Exercise Physiology: Energy, Nutrition and Human Performance, sixth edition. Lippincott Williams and Wilkins, Baltimore.