Illustration by Cathryn Cunningham / Journal

Before I give you some pointers about hydration during exercise, I have to tell you that this is a controversial topic. I will go back to the beginnings of the marathon to illustrate this controversy.

At the 1904 Summer Olympics in St. Louis, the men’s marathon was held at 3 p.m. on a hot day at around 90 degrees over dusty, dirt roads. Under these uncomfortable conditions, there was only one water station available for the entire 24.85 mile route. In fact, coaches and athletes at the time believed that drinking water was unnecessary and even harmful in races like a marathon.

In the end, only 14 out of 32 runners were able to cross the finish line. You can assume that the lack of studies at this time could justify the behavior of coaches and athletes. In fact, research studies conducted in the 1960s showed that at the end of a race, the winners or top finishers were the most dehydrated. Based on this data, it was easy for coaches and athletes to conclude that dehydration is necessary to maintain performance and that hydration should not occur. In short, if you want to win a race, don’t drink!

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Although this interpretation doesn’t reflect causality, the authors also showed that three of the top four runners had a body temperature (measured with rectal thermometers) above 104 degrees Fahrenheit and the winner had the highest temperature at 106 degrees. It was fascinating how these high body temperatures did not cause heat sickness.

The 1970s saw a rapid increase in non-competitive running and racing events around the world. Occasionally, these races were sometimes faced with unexpectedly hot conditions, resulting in a high incidence of heat-related medical emergencies.

In addition, research on exercise and hydration – mostly done in a laboratory – began to show that dehydration interfered with exercise performance. The scientific reports showed that dehydration during exercise was also linked to heat intolerance, impaired cognitive performance, and induced low blood pressure. These changes were seen with losses of only 2% of body weight.

In the 1990s, influenced by these scientific reports and the sports beverage industry, the recommendations of coaches, nutritionists, and coaches were to replace any fluid lost during exercise.

The scientific community postulated that replacing all fluid loss or drinking as much as possible would maintain exercise performance and eliminate the risk of heat illness.

As a result of this drinking protocol, the incidence of a serious condition called exercise-associated hyponatremia increased and deaths among endurance athletes have been reported. The pathogenesis of this disease is still incompletely understood, but it largely depends on excessive water intake, which lowers the concentration of sodium in the blood.

It is important to note that hyponatremia events are limited to long distance races such as marathons, triathlons, and ultramarathons.

More recently, research has shown that some level of dehydration (up to 2% of body weight) is okay during exercise. Also, it is safe for most of the exercising population to drink to the point of thirst.

Here are the current recommendations for fluid replacement during exercise:

Before training: Before training, in addition to regular meals and hydration, you should drink beverages to ensure that you start a training session with adequate fluid levels. This pre-workout hydration should be initiated several hours before the workout to allow fluid intake and adjust body water to normal levels.

During Exercise: The main message here is to listen to your thirst and avoid excessive dehydration (more than 2% body weight loss due to lack of water). If the training session lasts longer than an hour, consider consuming drinks that are high in electrolytes and carbohydrates, such as sports drinks.

After exercise: The replacement of fluids and electrolytes can be achieved through normal eating and drinking. If exercise resulted in excessive dehydration (more than 5% body weight loss due to lack of water), it is recommended that you encourage more aggressive fluid and electrolyte replacement.