During exercise, working muscles convert chemical energy into motion, but much of that energy becomes heat. If the body cannot remove heat fast enough, core temperature rises and performance drops. Thermoregulation is the set of body processes that keeps temperature near a safe range.
For athletes, staying cool helps protect the brain, muscles, heart, and hydration balance.
Key Facts
- Normal resting core body temperature is about 37 °C, and intense exercise can push it above 38 °C.
- Heat balance can be summarized as heat stored = heat produced - heat lost.
- Evaporation removes heat when sweat changes from liquid to vapor on the skin.
- Sweat rate can be estimated by sweat rate = body mass lost / exercise time, after adjusting for fluids consumed and urine lost.
- Skin blood vessels widen during exercise heat stress, increasing blood flow to the skin for cooling.
- Heat index and wet-bulb globe temperature help estimate heat risk because humidity reduces evaporative cooling.
Vocabulary
- Thermoregulation
- Thermoregulation is the process by which the body controls its internal temperature despite changes in activity and environment.
- Evaporative cooling
- Evaporative cooling is heat loss that occurs when sweat absorbs energy from the skin and turns into water vapor.
- Vasodilation
- Vasodilation is the widening of blood vessels, which increases blood flow to the skin and helps transfer heat away from the body core.
- Core temperature
- Core temperature is the temperature of the body’s internal organs and deep tissues.
- Heat illness
- Heat illness is a harmful condition caused by excessive heat strain, ranging from cramps and heat exhaustion to life-threatening heat stroke.
Common Mistakes to Avoid
- Assuming sweating alone means the body is cooling effectively is wrong because sweat must evaporate to remove heat. In humid air, sweat may drip off the skin without much cooling.
- Ignoring fluid loss during long activity is wrong because dehydration reduces blood volume and makes it harder to send blood to both muscles and skin. This can raise heart strain and core temperature.
- Wearing dark, non-breathable clothing in hot conditions is wrong because it can trap heat and reduce airflow over the skin. Light, breathable fabrics support radiation, convection, and evaporation.
- Thinking heat illness only happens on extremely hot days is wrong because high humidity, intense exercise, poor acclimatization, and heavy gear can all create dangerous heat stress.
Practice Questions
- 1 An athlete weighs 72.0 kg before a run and 70.8 kg after a 90-minute run. The athlete drank 0.5 L of water and did not urinate. Estimate the sweat rate in L/h, using 1 kg of body mass loss as about 1 L of fluid.
- 2 A runner produces 900 W of metabolic power during hard exercise, and only 180 W becomes useful motion. How many watts are released as heat?
- 3 Two athletes run at the same speed on a 30 °C day. One day has low humidity and strong airflow, while the other has high humidity and still air. Explain which conditions make overheating more likely and why.