High Heat and Humidity Warning
June 22, 2025
High heat and humidity leads to two problems in the exercising body:
- Increased body core temperature; and
- Dehydration
Increased body core temperature:
Increased body temperature (hyperthermia) leads to decreased muscle endurance.....which means the muscle’s ability to contract repeatedly or in a sustained manner over long periods of time.
High core temperatures also cause a shift in energy production......from aerobic to anaerobic mechanisms.......which means the body has to use up its muscle energy stores more rapidly.
Unfortunately, during a longer athletic event, the rate of adding energy (sports drinks, energy bars, gels, etc.) can't keep up with the rate of losing energy when heat and humidity are high.
Finally, high body temperature causes a decrease in blood flow to the heart as blood pools in the limbs. If the heart doesn't get as much blood, it can't pump oxygenerated blood back to the muscles.
Dehydration
Dehydration often occurs long before some athletes realize it or before cramps set in. Athletes can lose as much as 2% to 8% of their body weight during high intensity exercise, and the rate of fluid absorption from the gut, just can’t keep up with that rate of loss.
Dehydration causes a decrease in VO2max…….which means the body can't utilize oxygen as efficiently to provide energy.
Dehydration also contributes to the decrease of heart blood pumping mentioned above.
Action :
Fluid replacement is critical for events in high heat and humidity.
Players should start fluid replacement before a game, continue during the game and continue long after the game.
Drinking to quench thirst and keeping urine clear (not dark yellow) are good measures. Wearing light-weight, light-colored clothes of open-weave natural fibers (cotton, wool) or fluid-wicking fibers which helps increase evaporation and cool the body.
