Charlotte Lok, Bsc (Hons) Food Science and Nutrition

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Athletes need a healthy balanced diet to perform at their best, but nothing is more important than staying well-hydrated.

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Almost 70% of the human body is composed of water, so it is fair when we say that water is a vital resource for human survival. It is important to drink more when we engage in physical activities as we tend to sweat more and lose body fluids, and this is especially true for athletes who train and sweat daily. However, athletes who are searching for ways to gain a competitive edge often don’t pay enough attention to this simple fact: fluids are one of the best performance enhancers around, because even slight dehydration – the loss of about 1% of your body weight (that’s less than 1kg in a 100kg person) – can impair athletic performance.

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What is Dehydration and How Does It Happen?

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Simply put, dehydration is an imbalance in the body’s fluids, such that fluid intake doesn’t replace fluid loss, impairing the body’s normal functions. When you exercise, heat is produced by the activity, and this heat is transferred from the body core to the skin, where it can be dissipated. 

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Some heat can be radiated from the skin, but most heat is lost through evaporation – we begin to sweat, and the water evaporates off the skin surface, helping to keep us cool. Additional water losses happen when we breathe, or via the digestive system and urinary tract. But the body only has so much fluid on reserve, and the rate at which we lost water can be affected by several factors – losses increase as exercise intensity increases, and when conditions are especially hot and humid.

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What Happens When You Get Dehydrated?

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When dehydration happens, the volume of fluid in your blood vessels drop, which can affect your circulatory system. Less blood flows to the skin, impacting evaporation and causing the heart rate to rise as a result of the body working to keep you cool. Sweating also causes losses of more than just water, but you also lose important body salts – notably sodium and chloride, but also magnesium, potassium and calcium.

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By losing 1-2% of your body weight from sweating, your performance will be impacted negatively; reaching 3% of body weight loss will bring increased risk of heat cramps, heat exhaustion and heat stroke. The early warning signs of dehydration include dry mouth, thirst, headache and fatigue. As dehydration progresses, muscle spasms (cramps) can occur from sodium loss; further heat stress can bring on weakness, dizziness and nausea. 

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How Can Athletes Prevent Dehydration?

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Athletes lose between one and two litres of sweat per hour of continuous exercise. You can tell you’re getting dry because you’ll get thirsty, but you’re probably more than a little hydrated by then. Urine colour and volume can be an estimate to your hydration status, but it does not help you quantify the amount of fluids you need to replenish.

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Therefore, athletes are advised to drink on a schedule, as it is one of the best ways to help them be on top of meeting their needs and replacing fluid loss. Athletes who do not drink on a schedule tend to replace only half of the water they lose during exercise.

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How to Hydrate Through Your Workout Sessions

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Before Exercise: Start out well-hydrated. Drink freely for 24 hours prior, then have 2-3 cups of fluid 2-3 hours before the event. Then, have at least 150-300ml of additional water about 30 minutes before starting.

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During Exercise: Aim to replace sweat losses which may be 1-2 litres an hour. It may be difficult to replace all your losses, but most athletes can manage 500ml to 1 litre per hour by drinking every 10-20 minutes. Choosing a sports drink with salts (sodium, chloride, potassium, magnesium) as well as some carbohydrate will help maintain blood sugar and keep electrolytes in balance.

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After Exercise: Athletes are often advised to weigh themselves before and after an event or workout to estimate how much they need. For every 0.5kg lost, 2-3 cups should be taken in. While plain water quenches thirst, gulping plain water in a short period of time post-workout can give you a premature sense of satiation and may affect your hydration efforts. Choose beverages that contain salts and carbohydrate can replenish the body’s carbohydrate stores and facilitate water absorption.

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