As the weather turns on us, sometimes heading out into the cold and rain to complete a training session can be unbearable. Now with things like Wattbike and Zwift, indoor training has never been so popular. But don't compromise your nutrition just because you are exercising indoors.

When exercising the body’s heat production is 15-20 times greater than at rest. This can be elevated even further by conditions faced when training indoors, which lets face it, are often hot, humid and very sweaty. This is because there is little air movement causing heat to build up around the body meaning sweat can’t evaporate as quickly. This is why you get more hot and sweaty then you would get training outside, making you far more susceptible to dehydration.


Understanding Dehydration

Our body’s core temperature is ≈37°C and it is the thermoregulatory systems job to maintain this homeostasis. As the body’s core temperature rises due to exercise, the majority of the heat being dissipated is by the evaporation of sweat. Blood flow has to split itself between our organs, working muscles and now our skin for sweating. As the intensity of exercise increases, sweat rates will increase which actually reduces our blood volume and stroke volume. The heart then has to work much harder to deliver oxygen to working muscles and therefore lowers intensity of exercise we can maintain.

Not only do we lose fluid through sweating but also electrolytes. The primary electrolytes present in sweat during exercise are sodium and chloride with smaller amounts of magnesium, potassium and calcium also present. It is when this electrolyte equilibrium is not maintained during exercise, often through erroneous feeding strategies, that performance is further compromised.

Basically: Dehydration negatively affects performance. Even as little as 2% loss of body weight due to dehydration has been shown to impair performance


Practical Advice

Before Exercise: It is always a good idea to try to start every session fully hydrated. It can take around 8-12 hours of normal food and drink consumption to fully hydrate again post exercise so take this into account if training twice in a day. If you do not have this long in between sessions then fluid intake may need to be elevated above normal levels in order to rehydrate. The best method is to slowing sip an electrolyte beverage. A top tip is to keep checking your urine colour as a measure of hydration status as everyone is different; aim for a light straw colour.

During Exercise: Due to huge variation in individual sweat rates and indoor training conditions it is impossible to give an exact amount of fluid that should be consumed during a session. Differences in individual sweat rates can range from 0.4L to 1.8L per hour. The best idea is to develop your own individual hydration strategy specific to your own sweat rates.

One simple method is to weigh yourself before and after a training session. To keep it simple, a one hour session can give you a good idea of your sweat rate during an indoor training session.

Follow these simple instructions:

• Weigh yourself naked immediately before exercise.
• Train for one hour and monitor how much fluid you take on board.
• Weigh yourself again naked immediately after exercise.
• After exercise the calculated change in body weight will give you an indication of fluid loss.

For Example:
Ambient temperature: 25°C
Pre-exercise weight: 70 Kg
Post exercise weight: 69.5 Kg
Fluid volume consumed during exercise: 500ml
This indicates your sweat rate would be 1ltr/hour (70Kg-69.5Kg = 500g + 500ml = 1)
Under these conditions you can plan a hydration and fuelling strategy based on drinking 1ltr/hour.


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Thirst can also be a good way to dictate when to drink. As a rule of thumb it is always good practise to stay just ahead of that feeling of thirst. Consuming electrolyte drinks, such as OTE Hydro Tabs, will aid the absorption of fluid and also promote the feeling of thirst and further drinking. This is more beneficial than consuming just plain water.

Remember, any weight lost directly after exercise is sadly not miracle weigh loss but water loss. Text book would say replenish this with 1.5 times the amount lost (1kg lost= 1 litre lost) as soon as possible. Sipping little and often is better to help our bodies retain the water and stop us running to the toilet at every opportunity.

So next time you are ready to tackle that indoor session, make sure you consider you hydration before, during and after to get the best out of your workout.



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