Importance of Hydration for Exercise


We all know water is essential for life and dehydration to the most extreme cases can cause death. There are also many liquids that we consume that contribute to dehydration that many people are unaware of. Hydration for exercise is imperially important, a small level of dehydration can reduce the efficacy of your workout by a drastic amount. Not to mention the cognitive functions of the brain that rely on water to run smoothly.

Some fun water facts before starting:

1. An infant’s total body water is around 70%, children 65%, adults 60%, and elderly 55%.

2. Muscle contains 70-75% water, and fat contains 10-40%.

3. Between 5-10L of water is expelled and renewed each day.

4. Water loss of 10-20% of body mass is likely to cause death.

5. Your brain is ~ 80% water.

Insane in the Membrane – the importance of hydration for the Brain

As mentioned above, your brain is roughly 80% water. We all know the importance of our brains for both executive and non-executive function, and water is essential for these to run properly. An analogy you might understand is a rise in a CPU’s core temperature has a direct negative effect on the systems operating speed and efficiency, this can be relatable to dehydration of the brain. There are many published studies on the detriment of cognitive function due to dehydration with statistics and specific measurements over the past century, and consensus on the studies provide evidence that dehydration leads to reduced alertness, increased fatigue, slower recovery times, headaches, confusion, and a long list of other reduced abilities (1).

Dehydration on Exercise

It is increasingly important to make sure that you are properly staying hydrated during exercise. We advise all our personal training clients to bring a water bottle with them so they can easily hydrate during exercise (we also have a bottle filler to keep that water flowing). With vigorous exercise, it is not uncommon for a 200lb person to lose over 3L/hour, which is around 3% total body water loss. Most studies on the effects of dehydration in muscular and cognitive function are done at a 2% body water loss (2), so we can hypothesize if you have an especially sweaty client, they should be replenishing those liquids quickly to optimize performance. The specific study cited above includes a meta-analysis of 33 studies on 413 participants. The study showed significant correlation of dehydration at 2% reduction of body water loss and attention, executive function, and motor coordination. Additionally, another study was done on the effects of dehydration on combat athletes and muscular endurance. In their study they found a 28% decrease in muscular output in the non-control group during exercise (4).


Although there is much more to unpack on the topic of dehydration, I hope that this information was insightful and will encourage you to hydrate effectively for all facets of life. The detriment of dehydration on the functions of our daily lives should be a great motivator to keep tabs on your liquid consumption. This increasingly grows important as muscle composition degrades in age and our bodies carry less water, an impactful water deficit in an elderly person will be much less quantity than a youthful athlete. References