Shannon's health and fitness blog

Caution: Hot summer days ahead

Summertime is upon us, and with it comes the risk of heat illness.  Exercising in the heat can be risky if you don’t prepare ahead of time.  It is critical to maintain hydration when exercising in the heat.  Not only does exercise performance decrease with fluid loss, but the effects of heat and dehydration on the body can be a recipe for disaster.

A major consequence of dehydration is an increase in core body temperature.  Body temperature will increase 0.15-0.2 degrees Celsius for every 1% of body weight lost due to sweating.   This increase in thermal strain leads to greater cardiovascular strain.  Heart rate will also increase 3-5 beats a minute for every 1% of body weight lost from dehydration.  In an effort to prevent the body temperature from rising to dangerous levels, blood will be diverted from the organs to the skin.  This means that less blood and oxygen are getting to the working muscles, leading to a decrease in performance and an increase in the perception of effort.

To reduce the risk of heat illness, hydration and acclimatization are very important.

Before exercise Drink 500 ml of water 2 hours before exercise (Armstrong 2000, Casa 1999b)

During exercise Drink 200ml every 15-20 minutes, aiming to match fluid intake to sweat loss. (Casa 1999b)

After exercise Drink 1 liter (L) per kilogram (kg) of weight lost during exercise (Armstrong 2000)

Sodium Sodium intake is necessary only if exercise lasts more than 60 minutes or if the individual has a sodium deficiency.  Consume 0.5-0.7 gram per liter of fluid before, during, and after exercise.

Recommendations for heat acclimatization

  • Attain adequate fitness in a cool environment before attempting to acclimatize in the heat
  • Exercise at 50% intensity and gradually increase the duration and intensity of the workouts during the first 2 weeks
  • Perform highest intensity workouts during the cooler morning or evening hours and lighter training during hotter times of day
  • Monitor body weight to ensure that proper hydration is maintained as sweat rate increases

Also, monitor children even more closely as they do not have the ability to regulate temperature that adults have.

Don’t let summer ruin your exercise program.  Taking the necessary precautions will help you get the most out of your workouts and greatly reduce the risk of heat illness.


June 13, 2010 - Posted by | Health | , , , ,

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