D4 - Thermoregulation

• The core of the body consists of the head, chest and abdomen.
• • The skin temperature of the body can vary a great deal; however, if the core temperature is increased or decreased by 1 ‘C or more, this will affect a person’s physical and mental performance.
  • Larger changes in core temperature will lead to hypothermia or hyperthermia, both of which can be fatal.
• • In order to assess the core temperature of a person, there are a number of places a specialised thermometer can be placed: the mouth, the ear, the rectum or under the arm.
  • For sport scientists, the ear is the most common site for measuring core temperature, or, if the exercise allows, the rectal thermometer is used as this gives the most accurate readings of the true body core temperature.
• Heat Transfer

  • There are four different methods of heat transfer, some of which can be used to rid the body of excess heat and others which can be used to gain heat.
• Conduction - Place your hand on the desk in front of you. How does it feel? If it feels cold then you are losing heat to it via conduction; if it feels hot then you are gaining heat by conduction. Conduction involves the direct transfer of heat from one object to another. Normally this method of heat loss is not significant unless a person is exercising in cold water. This is because water conducts heat away from the body approximately 25 times more quickly than air. At the same temperature, a person in water will lose heat from the body two to four times faster than in air.
• Convection - Blow air over your hand. How does your hand feel? Your hand probably will have felt cooler after having air blown over it. This blowing of air molecules across your hand is the basis of convection. As air molecules are moved across the body, heat will be lost because convective air currents carry the heat away. Wind will increase the flow of air over the skin, thus increasing the amount of heat lost through convection. This is why a breeze feels good on a hot day and why we use fans to help keep us cool.
• Radiation - The process by which heat is lost to cooler objects in the environment, such as the floor, walls, trees and so on. How much heat a person loses through radiation is determined by their size, mass and body composition. People with a high body fat percentage will lose less heat through radiation than a person with a low body fat percentage, because body fat acts as an insulator to radiative heat loss. In contrast, a tall slim person will lose more heat through radiation than a short stocky person. In warm climates, sun radiates heat to the body, which will increase its temperature.
• Evaporation of Sweat - In humans, evaporation of sweat from the body is the major method of heat dissipation, particularly during exercise. Heat is transferred continually to the environment as sweat evaporates from the skin’s surface and produces a cooling effect. However, if the environment is humid, evaporation heat loss is reduced. Heat is only lost when sweat evaporates, which it will not do in humid conditions. Therefore, on a hot, humid day, an athlete can be dripping with sweat, but because the sweat is not evaporating, it does not cool them down.