Hydration! Inside vs. Outside

Hydration! Inside vs. Outside

ON 2015年4月29日 by Andrew Burke


Bonking is never fun! When you go outside, you pack a number of water bottles with the right amount of electrolytes. But when you stay inside, it’s easy to forget that hydration is just as important. We asked Annie Simpson, Performance Nutritionist, over at OTE Sports (Official Nutrition Partner for Team Lotto Jumbo)  why hydration is key and how it differs when riding inside.

Have you noticed that you get more hot and sweaty indoors then you would when training outside? When exercising, the body’s heat production is 15-20 times greater than it is at rest. This can be elevated even further by indoor training conditions which – let’s face it – are often hot, humid, and very sweaty. When you’re indoors, there’s little air movement, so heat builds up around the body and sweat can’t evaporate as quickly, making you more susceptible to dehydration.

Understanding the Effects of Dehydration

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

As our body’s core temperature rises, the majority of that heat dissipates through sweat. And as our exercise intensity increases, so do sweat rates.

image2When we sweat, we lose fluid and electrolytes. The primary electrolytes present in sweat during exercise are sodium and chloride, with smaller amounts of magnesium, potassium, and calcium. When this electrolyte equilibrium is not maintained during exercise, often through erroneous feeding strategies, performance drops further.

Preventing Dehydration

Before exercise: It’s 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 after exercising, so take this into account if you’re training twice a day. If you don’t have this long in-between sessions, your fluid intake may need to be elevated.

The best method for hydrating is to slowly sip an electrolyte beverage. Check your urine color to measure your hydration status; aim for a light, straw color.


During exercise: Due to the variations in individual sweat rates (which can range from 0.4L to 1.8L per hour) and different indoor training conditions, it’s impossible to recommend an exact amount of fluid that should be consumed during a session. Your best course of action is to develop your own hydration strategy specific to your sweat rates.

A one-hour indoor training session can give you a good idea of your sweat rate:

  • Weigh yourself naked immediately before exercise.
  • Train for one hour, and monitor your fluid intake.
  • Weigh yourself naked immediately 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: 70Kg
  • Post exercise weight: 69.5Kg
  • Fluid volume consumed during exercise: 500ml
  • Sweat rate: 1L/hour (70Kg-69.5Kg = 500g + 500ml = 1)

Under these conditions, you can plan a hydration strategy based on drinking 1L/hour.

Thirst can also be a good way to dictate when to drink. As a rule of thumb, it’s always good practice staying just ahead of feeling thirsty. Consuming electrolyte drinks, such as OTE Hydro Tabs, will aid the absorption of fluid, 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 weight loss, but water loss. The text book approach is to replenish this with 1.5 times the amount lost (1kg lost= 1 L lost) as soon as possible. Sipping little and often is better for retaining water and avoiding the need to run to the toilet at every opportunity.

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 Zwift workout.

OTE Sports Nutrition

This article has been edited and condensed.