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Hydration and its lesser-known aspects

Hydration and its lesser-known aspects


Physiotherapy student

Do you know what makes up 2/3 of our body and 75% of our muscles? Well, it’s water. Did you know that the thirst reflex is triggered when the body is already 1-2% dehydrated? It’s always been recommended to drink between 2 and 2.5 liters of water a day, but let me ask you: is it always advisable to drink so much water?

Its importance
We often ask ourselves what’s the point of drinking so much water? Overall, it enables nutrients such as glucose, proteins, lipids, vitamins and minerals to be transported in the blood to various sites, such as the muscles, for example. Water also eliminates the various waste products circulating in the body’s blood vessels. To give you a concrete example, during muscular effort, the CO2 produced by the muscle and released into the bloodstream is carried to the lungs by the presence of water, enabling it to be released back into the atmosphere. Finally, water is considered our body’s heat pump. More specifically, during physical activity, the body is transformed into a veritable furnace. The water in the muscle cells captures this heat and carries it to the surface of the skin, where it is dissipated by evaporation. This is how water is needed to maintain proper thermoregulation.

Electrolytes are small molecules (sodium, potassium, magnesium, etc.) essential to the body’s proper functioning. Present in the bloodstream, their levels must remain stable, as an imbalance could lead to dehydration. In such a situation, it is not recommended to rehydrate with regular water alone, as this would have the opposite effect to that desired, i.e. it would further dilute the electrolytes present in the blood, which can be very dangerous.

Signs and symptoms of dehydration:
– Very dark urine
– Intense thirst
– Dry mouth
– Severe dizziness
– Confusion
– Impaired vital signs
– Significant loss of electrolytes

Here’s a recipe to replace sports drinks, which are often far too sweet:
600 mL water
360 mL unsweetened orange juice
½ teaspoon table salt
** Recipe from CHU de Saint-Justine, Montreal

Hydration: a highly controversial subject
Several studies have shown that slow, progressive dehydration leads to problems with body thermoregulation, resulting in a fairly significant rise in body temperature (0.5 – 1°C). This will result in muscle fatigue and an increase in heart rate (around 10-20 beats for the same exercise intensity). It has been shown that the percentage of dehydration, weight loss and loss of physical capacity are proportional. In other words, the higher the percentages of dehydration and weight loss, the more persistent and intense the symptoms, and the more marked the reduction in physical capacity. So far, this theory is the best known in the world of sport. On the other hand, in recent years, numerous studies seem to be demonstrating the opposite…

In 2011, Université de Sherbrooke researcher Éric Goulet carried out a meta-analysis of cyclists to demonstrate that dehydration leading to a body weight loss of up to 4% would have no negative impact on performance, whereas to optimize performance, it would be more beneficial to drink according to thirst. We’re talking here about endurance events such as marathons, for example. Several studies have shown that overhydration can cause abdominal discomfort and hyponatremia (lack of salt in the blood). Indeed, hyponatremia can be a major risk factor (coma, convulsions, respiratory failure if uncontrolled) for endurance athletes, but there is no solid evidence that taking electrolytes during activity could prevent it. In fact, a study conducted by the research team of Dr. Hoffman on ultra-marathon runners (161 km), found that sodium intake in supplement form did not reliably predict blood sodium concentration at the end of the race.

The study also revealed that sodium consumption is indirectly linked to weight loss during running. This means that the more supplements a runner ingests, the less weight he or she will lose because of water retention. This sounds advantageous, but on the contrary, it has been observed that a loss of around 3-4% of initial body weight would be beneficial for sports performance, mainly in endurance runners. In fact, it’s possible to observe a loss of up to 10% among winners of several marathons, without any consequences for their health. In short, it would be desirable and advantageous to avoid preventing weight loss during long performances such as marathons.

Finally, according to the analysis of several studies, hyponatremia is mainly caused by overhydration rather than by not consuming sodium during the race. So it’s best to drink according to your thirst.

In conclusion, the aim of this article is not to make you change your habits if you’ve found your winning recipe. The aim is simply to show you that hydration is a more complex subject than it first appears, and one on which research continues in order to better understand the optimal level and method of hydration. Don’t forget to keep well hydrated every day, before, during and after your workout.

Written by Andrée-Anne Théberge, physiotherapy student

References :
1. Ledoux, Lacombe and St-Martin. Sport and performance nutrition. Collection Géo plein air, 2009, p.67-72.
Côté, Claude H. (Fall 2016). Theme 4: Fiber types and muscle fatigue. Course notes. [PDF]. PHT-1000: Musculoskeletal system: from the laboratory to the clinic, Université Laval.
2. Goulet, E.D.B. (2011) Effect of exercise-induced dehydration on time-trial exercise performance: a meta-analysis. British Journal of Sports Medicine. 45, 1149-56.
3. Dion, T. Courseà (online). Is dehydration bad for endurance performance? (page consulted March 11, 2017).
4. The runner’s clinic (online). Drink before you’re thirsty? (page consulted March 11, 2017).
5. The runner’s clinic (online). Electrolyte supplements to prevent hyponatremia? (page consulted on March 11, 2017).

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