Hot weather and indoor training can make it difficult to maintain optimal hydration, dehydration is not healthy but it is always important to remember it is possible to overconsume fluids during exercise. Too much water during exercise can cause the sometimes fatal condition hyponatremia, (literally low sodium) often known as water intoxication.
One of the adaptations to training is a reduction in the amount of sodium lost in sweat. However, as sweat rate increases the sweat gland has less time to recover sodium so if you are sweating a lot more than usual you may need to increase consumption.
Hyperhydrating prior to tough sessions by drinking 400-800ml of strong electrolyte solution -double up on electrolyte fizz tabs could be a useful strategy and the same after exercise in addition to a good protein recovery drink. REMEMBER water alone will just increase urine volume after exercise, this is one situation where you really benefit from sodium.
Getting hot and dehydrated during some sessions can have beneficial effects. The body adapts by increasing plasma volume, this reduces haematocrit level and EPO is produced to bring the level back up. The net result is an increase in red cell volume. NB Chronic dehydration is not healthy and will have a negative impact on health, performance and adaptation;- ensure you rehydrate properly after exercise.
During exercise, it is important to balance hydration and energy needs. If hydration needs are high and energy needs low then superhydration drink mix is optimised to deliver more hydration to the right body compartment.
For most indoor sessions Training Mix can maintain energy levels without fear of compromising fat burning. The special slow-release sugar used in Training Mix has been shown to work well in hydration drinks (Amano, 2019), making it a good choice for most zwift sessions. OK, if you want to race for several hours it may be beneficial to switch to a regular energy drink like Energy Mix but for sessions less than 90 minutes Training Mix can be a great option.