In order to avoid hyperthermia, heat exhaustion or heat stroke, the body is equipped with mechanisms to prevent large changes in temperature. Exercise is a high-energy state, requiring the breakdown of nutrients to fuel muscle contraction. The increased metabolism observed in muscles is correlated with elevated tissue temperatures. Adaptations in blood flow and sweat production serve to regulate heat removal during muscular exercise.
Muscle Activity During Exercise
The work of exercise requires energy. Your muscles breakdown nutrients, such as glucose and fat, into more readily processed forms of energy. Adenosine triphosphate, or ATP, is a ubiquitous form of energy used by muscle cells throughout the body. Your cells are constantly producing and breaking down ATP and these chemical reactions produce heat. When you begin exercising, the rate of ATP turnover increases tremendously, thus increasing the temperature of the muscle as a whole.
Body Temperature During Exercise
When multiple muscle groups begin contracting and increasing their activity, large amounts of heat are produced. In accordance with basic laws of thermodynamics, the heat will flow away from its site of production, and increase the temperature of the surrounding fluid and blood. Most biochemical reactions occur optimally at a specific body temperature, however, muscle activity during exercise often leads to increases in total body temperature. In order to maintain the status quo, your system will work hard to regulate heat during exercise.
Directing Blood to the Skin
Your body has the capacity to filter off excess heat energy if temperatures increase above a certain point. The first step in this process is transporting the heat from muscle tissue to the surface of the skin. This is accomplished through a process known as vasodilation. Capillaries, the smallest blood vessels in the body, are capable of increasing their diameter to accommodate large volumes of blood. According to the article “The Science of Exercise” at MayoClinic.com, blood flow to muscles may increase 100 fold, thus facilitating the removal of excess heat. Subsequently, capillary networks near the surface of the skin will dilate to increase blood flow and facilitate the removal of heat from the body. This is why your face may turn red during exercise; through vasodilation of capillaries in the skin, your body is attempting to expel the excess heat you are generating in your muscles.
The second step in the process of removing heat from the body involves cooling the skin with sweat. As the temperature of your skin rises, sweat glands will secrete a salty solution; this adaptation serves to cool the skin as evaporation causes heat removal. While this mechanism is highly effective in removing the heat of exercise, large amounts of sweat may be required during intense physical activity. It is important to stay hydrated during exercise so these essential regulatory pathways may properly control body temperature.