How to stay hydrated during indoor training

By Andy Blow | 7 Minute Read

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…


  1. The effects of heat on sweat rate during indoor training
  2. The effects of air flow and temperature on sweat rate during indoor training
  3. Tips for staying hydrated during indoor training
  4. Further Reading


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.


Sarah Crowley Indoor TrainingCredit: 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.


View this post on Instagram

Show us your Pain Cave to win our love (+ some PH goodies)! It's a well known fact that the main (and only) point of social media is to share every intimate detail of your indoor training set-up. So, who do you think lives in a Pain Cave like this? This pro triathlete recently returned from IM Florida, which is why you can still see the Canyon Speedmax SLX needs building back up, while his beloved Canyon Ultimate SLX Disc Road and commuter bikes are parked. On the Elite Direto trainer is a Canyon Aeroad Bike with 2 x high-powered fans for cooling. All of their indoor training is done on Zwift and the TV is tuned into the Global Triathlon Network (and sometimes Netflix + YouTube). A novelty cheque from Vietnam 70.3 - valued at 11.1 million dong - hangs on his wall, along with plenty of race numbers from around the world. If you look closely you might spot a umeke bowl from when he set the fastest military time & team time in Kona - a record which still stands today! And, of course, no Pain Cave is complete without a couple of PH Electrolitre bottles for hydration... This #PainCavePHoto was brought to you by... Team PH Captain Brad Williams ( @bw_tri )! Brad has got us started and now it's your turn - invite us into your Pain Cave and you could win a stash of PH. Gowaan, tag us in your #PainCavePHoto for your chance to win...

A post shared by Precision Hydration (@precisionhydration) on


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...


1. Before the session: 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.


2. 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.


3. 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.


4. 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.


5. 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

Andy Blow - Founder and Sports Scientist

Andy Blow

Founder and Sports Scientist

Andy Blow is a Sports Scientist with a BSc Honours degree in Sports and Exercise Science from the University of Bath. An expert in hydration, he has co-authored a number of scientific studies and books.

He was once the Team Sports Scientist for the Benetton and Renault Formula 1 teams and remains an adviser to the Porsche Human Performance Centre at Silverstone.

Andy has finished in the top 10 of IRONMAN and IRONMAN 70.3 races, as well as winning an XTERRA World title. It was his own struggles with cramp that led to him specialising in hydration and founding Precision Hydration.

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