Fluid Intake
We often talk about eating the right amount to support training, but what about drinking? Staying hydrated is an important part of health and recovery for athletes.
When you train, you lose fluid through sweat. You can replace this by drinking water during and after your session.
What are the different types of fluid loss by percentage of body weight, and what do they feel like in practice?
- 1–2%: You can feel thirsty, and performance can start to be impaired.
- 3–5%: You might feel nauseous, and your performance will be reduced.
- 5–10%: This is severe fluid loss, and you risk heat exhaustion or heat stroke.
- Above 10%: This can be very dangerous and requires medical attention.
Photo Woman drinking water
How Much Fluid Do You Need Per Day?
The typical guidance for most people is around 2 litres of fluid per day. However, athletes lose more than average through sweat, which is the body’s way of bringing their temperature back to normal. The amount of fluid lost through sweating depends on the person, temperature, and the duration and intensity of exercise, so the amount you’ll need to drink varies, too.
One way to ensure you’re rehydrating with enough fluid is by measuring your fluid losses. You can do this by weighing yourself before and after exercise to get a rough understanding of your sweat rate (we’ll cover this in more detail later in this article). You can also monitor yourself by paying attention to how thirsty you are and the colour of your urine.
Keeping a bottle of water with you throughout the day is a good way to make hydration easier. It can be easy to go through the day and forget to hydrate, so keep a water bottle to hand, and try to sip and drink to thirst throughout the day. You can also try having other drinks you enjoy, like herbal tea and water with added fruit or mint.
Photo Man drinking water
How to Check Your Hydration Status
A simple and practical way to monitor your hydration status throughout the day is to check the colour of your urine. Pale straw or lemon yellow indicates good hydration. Dark yellow or amber suggests you are under-hydrated and need to drink more. Very dark urine, especially first thing in the morning after a hard session, means that you are dehydrated.
Clear or colourless urine can indicate overhydration and is not a target to aim for. This method is most useful as a day-to-day guide and is a useful starting point to understand your hydration.
Measuring Your Sweat Rate
The most reliable way to personalise your fluid intake is to measure your own sweat rate. The method is straightforward:
- Weigh yourself immediately before training
- Roughly track how much fluid you consume during your session
- Weigh yourself again immediately after
Each kilogram of body weight lost equates to approximately one litre of fluid lost. After training, try to consume roughly that amount of fluid.
Over time, paying attention to how much fluid you usually lose when training can help you anticipate how much you need to drink. This can help you drink the right amount during training. Theoretically, you want to avoid losses of over 2%, though this can be difficult to achieve in practice, especially for endurance athletes. Try to do your best and gradually work on your hydration over time.
Electrolytes and Sports Drinks
For runs lasting longer than 60 minutes, especially in hot conditions, plain water might not be enough. Sweat contains sodium as well as smaller amounts of other electrolytes, so it’s a good idea to try to replace these with sports drinks containing electrolytes. This helps reduce your risk of dehydration and helps your body properly absorb the fluid.
Practical options include isotonic sports drinks and electrolyte tablets added to water. Sodium needs can vary from person to person, too. Some people are heavy sweaters (you might be one if you regularly have a white residue on your skin after a run). If you lose more sodium than average on your runs, you might want to pay particular attention to electrolytes on hot days or during long sessions.
We explore sports drinks in more detail in the Sports Drinks article. You can read it here.
References
Cheuvront, S. N. & Kenefick, R.W. (2022). Personalised Hydration Requirements of Runners, International Journal of Sport Nutrition and Exercise Metabolism, 32(4). https://pubmed.ncbi.nlm.nih.gov/17277604/
Sawka MN et al. (2007). ACSM Position Stand: Exercise and Fluid Replacement, Medicine & Science in Sports & Exercise, 39(2). https://pubmed.ncbi.nlm.nih.gov/17277604/