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Fuelling Performance | Exercise Nutrition | Step 2: Hydration

Ted Munson

Ted Munson

BSc, MSc, PG Cert, SENr
Performance Nutritionist

In step 1 of our Fuelling Performance guide to exercise nutrition, we discussed energy and its role in exercise.

Ever wanted to know how best to fuel your athletic endeavours?

We took your top questions to Ted Munson a top Performance Nutritionist to produce this series of blogs.

Exercise Nutrition: The Importance of Hydration

The body contains around 60% water and around a third of that water exists in extracellular fluids e.g your blood. This is also where the majority of electrolytes are stored. The main electrolytes are sodium, potassium and chloride. The most important electrolyte related to fluid balance and exercise performance is sodium. Sodium helps the body retain fluid so you can use it more effectively during exercise. It’s also needed to help nutrients absorb in the gut – yes it can aid the digestion of carbohydrate to fuel performance! Optimal levels of sodium also promote cognitive function and can help combat muscle cramping

The amount of fluids you should consume daily depends on many factors including heat, humidity, acclimatisation and activity levels.

To start – aim to consume 2.5L of fluid per day – water, fizzy drinks, tea, coffee etc all count, plus an extra 500 ml of fluid per hour of exercise. 

Also keep check of your urine colour which is a good indication of hydration. Aim to maintain a clear-straw colour. Note that some supplements and food like beetroot can alter urine colour

If you think you suffer with dehydration and the side-effects (headaches etc)- monitor your caffeine intake. Caffeine is a diuretic – so increases urine production. Alcohol is the same, so keep check!

exercise nutrition - hydration

Do I need to add electrolytes or just drink water?

When you sweat, you lose water along with electrolytes like sodium, potassium and chloride. You need to replace electrolytes, particularly sodium to aid hydration and performance. The issue is that everyone loses a different amount of sodium in their sweat. This is dependent on many factors including how acclimatised you are to heat, the type of exercise you’re doing, how much you sweat and what you’ve consumed pre-exercise. Sweat sodium levels have nothing to do with fitness, but your individual make-up!

The only way to determine your sweat sodium levels is to undergo a sweat sodium test, but if you regularly have salt crystallising on your skin or clothes after tough sessions or taste salty sweat, then this is a sign that you should include more electrolytes in your hydration strategy

Should I consume fluids to hydrate before a workout/race?

Pre-hydration is often overlooked and evidence suggests that athletes often start exercise in a dehydrated state. Pre-hydration is a strategy used by many athletes and recommendations are generally specific to your body mass:

Aim to drink 5-10 ml per kg of your body mass 1-2 hours pre-session, for example, a 70kg runner preparing for a 10km run would drink 350 – 700ml

If you’re undertaking exercise that will promote fluid loss (sweating) then you should include electrolytes in your drink – around 300mg of sodium/salt is recommended and is found in most commercial products. If you’re undertaking particularly tough exercise use this opportunity to consume additional carbohydrate such as our Performance Energy products.

How much water do I need to drink to stay hydrated during exercise?

Fluid intake during sessions depends solely on your sweat rate and there is no one size fits all recommendation. You should drink enough fluid to prevent the body from losing more than 2% of body mass through sweating e.g 1.4kg for a 70kg athlete. Any more than this and studies show performance can decrease through the effects of dehydration. We recommend you work out your sweating rate in training to find out what works for you:

In order to do this you’re going to use the following calculation during a test session; 

Body mass pre (kg) – body mass post (kg) + weight of any fluid consumed (kg)/ time exercising (h)

Aim to achieve similar conditions to what you experience during a hard session, sports competition or race where you’re worried about performance. For example;

An athlete undertakes a 1.5 hour interval track session, before the session he weighed in at 75kg, post-session: 73.2 kg* and 200ml of fluid was consumed during the workout.

75kg – 73.2kg = 1.8kg loss + 0.2 kg (fluid intake) = 2/1.5 (duration) = a sweat rate of 1.33L per hour

In this case the athlete lost 2L of sweat and only consumed 200ml of fluid, which is over 2% of body mass loss and performance may have been affected. They should have consumed around 600ml of fluid to maintain hydration levels. The addition of electrolytes would aid fluid retention and maximise hydration.

*Also consider weight that may have been lost during session by means other than sweating e.g urinating

How important is it to rehydrate after a workout?

Rehydration is key for recovery particularly if you’re planning on training again later that day or the next day. The amount of fluid you should consume post-exercise for maximum benefit depends how much fluid you lost during exercise. You should ideally aim to replace around 150% of the fluid lost during exercise.

In this case 1.8kg (1800ml) was lost through sweating – so the athlete should aim to consume an additional 2700ml of fluid in the hours/day after the session.

Looking for an all in one solution to fuel performance and hydration?

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