The Human body is made up of approximately 60% water* (by weight); water is involved in numerous functions within the body, which are vital for proper physiological functioning. Therefore it should come as no surprise that  losses in body water - aka dehydration - can have significant negative effects on our performance (both physical and mental).

Yet somehow, despite the fact that this knowledge is nothing ‘new’ or ‘groundbreaking’ (i.e. both the scientific and athletic communities are very aware of the importance of hydration), many of us are walking around in a dehydrated state and possibly detracting from our performance without even realizing it.

Despite a sense of general awareness many of us have a poor understanding of what roles water plays in our body, how exercise can influence hydration demands, and just how important salts/electrolytes are when rehydrating; and that is what I am going to go over in this post.

*Exact percentages vary between individuals and even within the same individual depending on factors like body composition and hydration status.

1.  Water in Our Bodies & Dehydration

More often than not water is something to which we give very little thought. We drink it when we feel thirsty (or perhaps have a headache) and if we have too much we end up making frequent trips to the bathroom.

There is more to it than that. Water is the medium in which all our cells ‘bathe’. Water is the solvent/transporter that dissolves nutrients we ingest and delivers them to various parts of our bodies. Water is part of almost every metabolic reaction within the body (metabolism) and in the absence of water we lose our ability to regulate body temperature, maintain proper muscle function and more.

Water loss occurs naturally as a result of normal physiological functioning; and throughout the day we can lose between 2-3L* through different mechanisms. Some losses are ones we are typically aware of

e.g. urination, sweating

but a large portion of our water loss occurs so subtly, we don’t even notice it.

e.g. through respiration (breathing), through our skin when we aren’t sweating noticeably

Some of our ‘lost’ water (up to ~1L) does gets replenished thanks to the foods we eat, however, that still leaves us with approximately 2L of water/day to replenish and, unfortunately, many of us don’t even come close to that with our daily intake.

“But whenever I’m thirsty I drink”

Unfortunately, thirst as an indicator for hydration is not the most effective as it typically only kicks in once we have lost ~1-2% water at which point our performance started to decline. Essentially, a large percentage of the population is walking around slightly dehydrated and underperforming without realizing it.

*Under normal conditions, i.e. no exercise/no extreme temperatures.  

2. Exercise and Water

Under ‘extreme conditions’ - e.g. exercise, intense heat (or both) -  we typically experience an increase in respiration, body temperature and sweat rate; all of which contribute to us losing water more quickly than normal and we must adjust our rehydration strategies accordingly. If we don’t, it doesn’t take long before dehydration will kick in and our performance will start to suffer.

A loss of just 1-2% body water is enough to decrease our ability to regulate body temperature* and produce an increased heart rate.**. By  4-6% water loss we will exhibit noticeably reduced muscle strength and endurance (as well as heat cramps), and by 6-8% dehydration we are running the risk of severe heat cramps, heat exhaustion, heat stroke, coma and even death.

Obviously these are some extreme examples of what can go wrong when dehydration gets out of control, and most of us (hopefully) will never be at risk of reaching that state. However, that doesn’t mean it's of no concern to us, particularly as athletes, because even minor dehydration affects our performance. And staying properly hydrated through training and competition increases our chances of success by a margin.

*less available water = reduced ability to sweat/cool off

**Blood is ~83% water, when dehydrated blood plasma volume decreases and the heart must pump harder in order to deliver the same cardiac output.

3. Electrolytes

Now that we have a (basic) understanding about water in the body, let's take a minute and talk about salts/electrolytes, because maintaining (or reestablishing) a hydrated state involves more than just ‘drinking water’.  

Without going into too much detail, essentially water within the body can be divided into two subcategories:

• Intracellular fluid (ICF) - “within the cells”
• Extracellular fluid (ECF) - “outside the cells

Each of which contains certain salts/electrolytes* (in varying concentrations) and the composition of these fluids plays an important role in their physiological functioning.

The exact concentration of electrolytes can vary depending on what's going on inside and outside of our cells, and our bodies are designed to deal with minor fluctuations and changes. However, substantial losses in body water (via excessive sweating or urination) can result in electrolyte imbalances because the rates at which we lose water and electrolytes differ. Which means, that avoiding (or reversing) dehydration takes more than drinking water, it requires intake of fluid(s) which contain electrolytes and can help to restore a balance

Luckily, ‘rehydration drinks/tablets’ are relatively easy to come by (just stop by your local pharmacy); however, we need to be careful with sports drinks because they often contain unnecessarily high amounts of sugar. During endurance-type activities some sugar is okay (as a matter of fact it can be a good thing) because it provides us with a readily available source of energy (glucose); but most commercial drinks have significantly more than the recommended ‘less than 10% glucose’.  

*ICF is typically high in Potassium (K) and Magnesium (Mg) but low in Sodium (Na) and Fluoride (Fl); whereas ECF is low in K and Mg but high in Na and Fl.

Final Thoughts

We invest so much time, money and effort in becoming better athletes

e.g. training programs, nutrition, massage, chiropractic treatments, supplements

But what would happen if we turned some of that energy towards understanding the importance of water in the body and making sure not to let something as simple hydration derail our performance?

That is it for now, but stay tuned for next week's post in which I will take a more in-depth look at dehydration during exercise and go into more detail about some rehydration strategies.

References/Further Reading

• Berardi, John. The Essentials of Sport and Exercise Nutrition.
• Sports Dietitians Australia. Fact Sheets: Fluids in Sport. Retrieved from here.
• Jeukendrup, Asker. Gleeson, Michael. Sports Nutrition 2nd Edition - Dehydration and its Effects of Performance.