Summer Lovin’: Body’s Responses to Exercising in Heat

With summer well under way, the human body undergoes various changes to keep cool in the heat. It adjusts through behavioural and physiological mechanisms as part of a thermoregulatory response, to keep the core body temperature at its optimal 37°C. Removing excess clothing, fanning yourself and moving into the shade on a hot day are some examples of behavioural responses to high temperatures. Physiological responses include changes in blood vessel circumference (which is why we become red-faced), slowing down your metabolism and sweating. Most of the heat accumulated by the body is lost through skin, with a small amount also lost through respiration.

When we exercise, the body generates heat due to the extra demands of physical movement. This is primarily as a by-product of energy production, as well as frictional heat produced by muscles. Therefore, when exercising in a hot environment, additional heat stress means that the body is challenged to maintain core body temperature at its optimal level. When the body is unable to dissipate the heat from the environment and exercise, it poses a risk of heat exhaustion. The effectiveness of the thermoregulatory response is weakened under uncompensable heat stress, which can lead to a decrease in exercise performance and fatigue.

There are two phenomena that occur when exercising in heat: sweating and cardiovascular drift. Sweating aims to increase evaporative heat loss. It lowers the temperature of the skin to allow a bigger temperature difference compared to the environment, increasing heat loss. Cardiovascular drift happens when blood flows to the working muscles and skin to lose heat by radiation, conduction and convection. Therefore, the cardiovascular system must work harder because there is more competition for blood supply and an increased burden of plasma loss due to sweating. As a result, heart rate increases to compensate for these changes.

Here are some tips and considerations for when exercising in the heat:

  • Shorter warm ups to prevent too much increase in core body temperature
  • Pre-cooling may be helpful
  • Be aware that HR will be higher
  • More rest between sets
  • Alter training times- cooler hours of day or train in the shade
  • KEEP HYDRATED- dehydration is a big issue so fluid intake is essential. Have regular, cool liquids with electrolytes.
  • Wear loose fitting clothing but this needs to be balanced with sun exposure. Be sun smart.
  • Keep monitoring yourself and people around you for any signs of heat stress

 

Sarah Chee

B.Sc. Biomedical Science (Human Biology Preclinical) (Honours), B.Sc. Exercise, Sports and Rehabilitation Science

Exercise Scientist

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