Indoor training can be viewed as an unfortunate but necessary evil by some athletes, while others relish the opportunity to get in the ‘Pain Cave’ and log those hours on the turbo trainer or treadmill.

There's often an impressive (and slightly dangerous) pool of sweat on the floor whenever I've finished an indoor training session. So, does that puddle mean I sweat more when training indoors than outdoors? Let’s find out…

The effects of heat on sweat rate 

The body controls core body temperature (CBT) to keep us alive and functioning, and we sweat when our CBT rises above a certain point.

The heat given off by working muscles has the greatest influence on CBT when exercising, so how hard you’re working has a massive impact on your sweat rate and more so than body fat, weight and overall size. This was emphasised by the findings of a recent study.

So, the average indoor workout is probably more intense than an outdoor session because we generally go for ‘quality’ over ‘quantity’ (unless you really enjoy being in your ‘pain cave’ for hours and hours on end). Therefore, this results in a higher sweat loss per unit of time.

Image Credit: Dale Travers ©

Air Flow and Temperature

Two other important factors which will impact on how sweaty you get when training indoors are Air Flow and Temperature:

Air Flow

When outdoors, you’re moving through air so you get some airflow past the skin. Air movement causes heat to be drawn away from the body’s surface more effectively (via convection and sweat evaporation) and this cools you.

On a static bike or treadmill, you lose this airflow and the sweat tends to drip off you, making you more aware of it. And as there’s no natural cooling effect, you probably actually do sweat a little more to compensate too (unless you attempt to mitigate the lack of air flow by adding a fan to your indoor 'Pain Cave'...).


Your body tries to offload heat to the environment when you’re training. The bigger the gradient between the air temperature, and the lower the humidity, the easier it is for heat to be evaporated away. As many places we train indoors are already quite warm and humid, the gradients for heat loss and evaporation are less pronounced than outside, and this further hinders thermoregulation and drives sweat rate up.

So, whilst you don’t necessarily sweat significantly more indoors than outdoors, there are reasons why total sweat loss might be higher some of the time.

Tips for staying hydrated during indoor training

There are five simple steps you can take to ensure that you are well hydrated for your daily indoor training session...

Before: Arrive well hydrated

As we mentioned earlier, most people’s indoor training sessions are short and intense as we go for the old ‘quality over quantity’ approach. So, it’s important to make sure you start hydrated by doing some form of preload as this will maximise your ability to thermoregulate by sweating.

Aim to drink around 500-750ml (16-25oz) of plain water mixed with a strong electrolyte drink (we recommend PH 1500) a few hours before you start your session. Use a bit of trial and error over the course of a few sessions to refine this approach.

Before: Don't overdo your fluid intake

Having said that, there’s no need to go overboard on fluid intake in the immediate build-up to your session. Just try to stick to good hydration practices on a day-to-day basis.

Before: Add sodium

If you do find yourself low on fluid leading up to a session, it’s a good idea to add additional sodium to your drinks in the preceding hours as this maximises absorption of the fluids you do consume.

During: Drink to thirst during the session

This comes back to the ‘don’t overdo it’ point. Ultimately, don’t interfere with what you’re actually there to do (i.e. get sweaty on the turbo or treadmill) by trying to taking on unnecessary amounts of fluid.

Recovery: Continue to drink to thirst and maybe add sodium to your food and drinks

If you feel like you’re losing the battle to keep up with what you’ve sweated out during your session, the best way to 'top up' is through electrolytes or SweatSalt Capsules. By doing that you give your body the best chance of rehydrating fully before you go through it all again the very next day.

Don’t forget to stay on top of your hydration when training indoors and following these simple steps will help keep you hydrated correctly and able to perform at your best.

Further Reading