Updated: Aug 15, 2022
Hydration and exercise - How do I know if I am well hydrated?
With the temperature rising over the summer, we tend to sweat more during exercise and it is extremely important being aware of why it is important to replenish any fluid lost as soon as possible, to avoid serious health conditions.
First of all, we know that water is a crucial element for life, representing around 45% to 70% of our body. Like oil in a car, water in the body (and fluid in general) is needed for different functions such as transporting nutrients and compounds in the blood, removing waste products through urine, regulating body temperature, allowing our muscles to contract and joints to move. In fact, water acts as a lubricant and shock absorber in your joints. For athletes dehydration can lead to reduced endurance, strength and heat-related illness. There is evidence reporting that with just 1.5% of dehydration our concentration and mental ability can be impaired. Ironically, we don't feel thirsty until we are 1-2% dehydrated - which means that we need to drink before we realise it otherwise we are likely to end up training being already dehydrated.
How much fluid do I need when I exercise?
Staying hydrated is essential for our performance, mental and physical health. Therefore, it is crucial to start each training session or competition fully hydrated. However, this is not sufficient as we need to drink appropriate fluids even during training and competitions and restore hydration levels as soon as possible afterwards, to replace any fluids and salts lost through sweat. Why salts? Because when we train at high intensity we sweat a lot and, therefore, we need to be sure to have enough salts in our diet to compensate for the losses.
In general, the British Dietetics Associations (BDA) recommends around 2 litres of water per day for men and 1.6 litres per day for women. However, these guidelines do not take into account physical activity and sweat rates, which vary among individuals. Therefore, it is extremely important to create a hydration plan and adopt personalised hydration strategies to avoid dehydration. Studies have shown that, depending on the environment temperature, our body size and exercise intensity we can lose from 1.5L up to 4L during physical activity - all these fluids would need to be replaced.
How to tell if you are dehydrated?
There are 5 major signs of poor hydration:
1. Being thirstier than normal
2. Having a dry mouth
3. Feeling tired with poor concentration and coordination
4. Headache, dizziness or feeling light headed
5. Dark urine - it should be pale yellow. Check it out!
An easy way to check how much fluid you have lost while training is to weigh yourself before and after your workout. This must be done in minimal clothing, taking into consideration any fluid intake during exercise (subtract any fluid consumed) and wiping off any sweat from your body post training. Every 1kg lost is around equal to 1 litre in sweat.
What types of fluids do you need?
Most people know that exercise and, in particular, training at a high intensity can lead to dehydration and pay attention to drink enough water before, during and after their workout. However, our body contains electrolytes, such as sodium, chloride, bicarbonate or potassium, which are minerals in charge of carrying out chemical reactions in our body and maintaining a steady blood volume. If you drink too much plain water you may end up diluting the body’s electrolytes, causing an electrolyte imbalance called hyponatremia. Therefore, if fluid losses during or after exercise are significant and you notice that you have a salty sweat, it may be necessary to include some electrolytes too.
What to drink solely depends on the type, intensity and duration of physical activity (and your goals). If you train at a low to moderate intensity for less than 1 hour with low sweat losses you only need water. If you train at a higher intensity with sessions lasting longer than 1 hour and great sweat losses you may need an isotonic sports drink or a home-made sports drink. Check my previous articles: “Ditch Lucozade.. try making your own sports drinks”.
If I don’t sweat a lot while training, does it mean I am not training hard enough?
Definitely not! Sweating is not an index of effort. We sweat because our core temperature increases and sweating is how our body cools itself. Sweat production is not only linked with an increased internal temperature due to our muscles working out, but it is also linked to the environmental temperature. In particular, when we train in a hot and humid environment our body temperature will keep increasing and, therefore, we must make sure to stay hydrated and replace any fluid lost.
Our top 4 tips to stay well hydrated:
1. Ensure you start training well hydrated. Check the colour of your urine: your urine should be a pale yellow colour. Aim to drink roughly 400 - 600 ml two hours before.
2. Be conscious of electrolytes: always add a pinch of salt to your homemade food. You won’t need to worry if you eat processed food as they are typically salted.
3. Instead of drinking water or your drinks all at once, try to sip water frequently over the day.
4. Following exercise, your body will continue to lose fluids. Aim to replace between 125-150% of the fluid you lost over the following 4-5 hours.
Francesca is our sports nutritionist who has experience working with athletes to help them understand their nutritional and hydration status. Book a free 15 min to see how Francesca can help you perform better.
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Bda.uk.com. 2020. Fluid (Water And Drinks). [online] Available at: <https://www.bda.uk.com/resource/ fluid-water-drinks.html>
BDA Bda.uk.com. 2020. Fluid (Water And Drinks). [online] Available at: <https:// www.bda.uk.com/resource/fluid-water- drinks.html>
Shirreffs, S.M. and Sawka, M.N., 2011. Fluid and electrolyte needs for training, competition, and recovery. Journal of sports sciences, 29(sup1), pp.S39-S46.
Stiller, S., Bonnie-Schorn, E., Grassmann, A., Uhlenbusch-Körwer, I. and Mann, H., A Critical Review of Sodium Profiling for Hemodialysis. Seminars in Dialysis [Internet] 2001.14(5), pp.337-347. doi: 10.1046/j.1525-139X.2001.00086.x