Hydration 101

Hydration is a key component for overall health and fitness, and optimising fluid intake around training sessions can aid in maximising performance. There is no doubt that too little or too much fluid can have negative consequences on exercise output and in some extreme cases fluid imbalance can be harmful to health. Planning how much (and perhaps more importantly what) to drink in the gym is a vital part of your nutrition routine.

Let’s take a closer look at the fluid in our body, what happens to this during exercise and what we can do pre, intra and post exercise to optimise hydration.

Total Body Water

When we look at fluid balance within the body this can be considered as an interaction between fluid losses and fluid gains, with a number of factors influencing both sides of this. On average, around 60% of the human body (by body mass) is made up of water, ranging from 40-75%, the total volume of this can be termed total body water. For a 70 kg individual this could mean 42 litres of fluid! The fluid within the body can then be found to be in two compartments or places:

• Intracellular – within the cells, accounting for 60-70% of total body water
• Extracellular – outside of the cells within circulation, accounting for 30-40% of total body water

The body at rest is normally in thermal balance and a state of euhydration, meaning a normal body temperature and a normal level of hydration. This normal level of hydration can safely fluctuate with natural fluid intake and losses throughout the day. The process of losing fluid is known as dehydration and excess dehydration can lead to hypohydration (a state of uncompensated loss of body water).

The Demands of Exercise

As we exercise, our increased muscle activity causes our body temperature to rise. The human body does not tolerate large changes in our core temperature very well, and we have developed sweating as a mechanism to keep ourselves cool. As we sweat, the fluid takes heat away from the skin as it evaporates. This cools the blood flow close to the skin, which helps to keep the core cool as the blood circulates to the vital organs around the body.

This sweat response can cause fluid and electrolyte loss from the body, and if not managed correctly during exercise, this process of dehydration can negatively impact performance. A 2-3% drop in body mass as a result of sweat loss is enough to have a negative impact, causing elevated body temperatures, increased muscle glycogen use, increased perception of effort and higher heart rates. All of which can contribute to wider reductions in mental and physical performance.

What Can We Do?

Given the negative effects of dehydration, starting exercise in a hydrated state and replacing fluids during exercise is crucial. Pre-hydration strategies would be to consume a fluid volume equivalent to 5–10 ml per kilo of body mass in the 2-4 hours before exercise; this would equate to 400-800 ml of fluid for an 80 kg individual in the pre-exercise window. As a general rule, make sure that your urine is straw-coloured before you start exercising. This is an indication that you are hydrated!

To effectively rehydrate during exercise requires more than water alone, as the body is always striving to keep everything in balance, including the balance of electrolytes in the fluid around the cells. Appropriate sodium intake along with fluid can optimise hydration, which is especially important when sweat rates are high. Practically, always have a bottle to hand in the gym. Standard bottles just don’t cut it any-more; try PhD’s 1.5 Litre water bottle or better yet their 2.2 Litre water bottle to save you being caught short without any water. Additionally, PhD’s Intra BCAA/ contains CocoMineral, a coconut water extract which contains the key electrolytes, sodium and potassium, helping you to replenish the electrolytes lost through sweat during exercise.

Post-exercise rehydration can be guided by acute changes in bodyweight, whereby if you weigh yourself before and after exercise, the difference is likely to equate to fluid loss. For example, an individual weighing 80 kg pre-exercise and 79.2 kg after exercise has effectively lost 800 ml of fluid. This should be replaced at the rate of 150% in the hours following exercise, so 1.6 litres in this case!

Key Points:

• Fluid balance is a relationship between the fluid lost and fluid taken in, which can be affected by exercise, environmental conditions, sweating and drinking.
• Dehydration beyond the point of 2-3% body mass loss through sweat can negatively impact performance.
• Hydration protocols should be in place pre-, during- and post-exercise to maintain hydration status.
• Drinking water alone is not enough – fluids taken in around exercise should also include other nutrients such as sodium and potassium.

Written by PhD Nutrition