Advice from the experts: Sweat it out

October 05, 2018 4 min read

Riding a Wattbike offers many advantages when compared to riding outdoors. You can cycle any time of the day, there’s no traffic and intervals may be performed with absolute precision. Further, with the advent of apps such asVirtuGO, you can team up with friends anywhere in the world and complete a training session; all from the relative comfort of your home.

However, that term ‘relative comfort’ is pointed at the one obvious disadvantage of training indoors: it’s hot. We all know the feeling of being covered in sweat from head-to-toe after riding inside. But sweat is just one by-product of a complex series of bodily processes that respond to exercising in a hot environment.

Understanding some of the body’s other regulatory systems and their limits is a step in the right direction to making your next indoor workout more efficient and more comfortable. In this last part of a two-blog series, VirtuGO delve deeper into the science behind hydration and gave us some tips on cooling down on the Wattbike.


When evaporative cooling cannot take place - as covered in our previous blog - performance will deteriorate and your enjoyment of training will be diminished. If inappropriate clothing is worn for a ride then the evaporation of sweat is further reduced and core temperature will rise.

The ability to cool off by sweating and evaporative cooling is dependent upon the availability of water. When water lost via sweating is not replaced, dehydration occurs. While mild to moderate work rates yield sweat rates of 0.8 – 1.4 litres per hour (L/h) one of the highest sweat rates ever recorded was 3.7L/h during the Marathon at the 1984 Olympic Games.

On the other side of the equation is fluid uptake. The maximum amount of fluid that empties from the stomach during exercise is 0.8-1.2L/h. It is clear to see here that at the upper limit of the normal range a sweat rate of 1.4L/h can only be combated with a rehydration rate of 1.2L/h. This explains why most strenuous bouts of exercise can mean a loss in body weight of 2-8%.

In a hot environment, small to moderate levels of dehydration (2-4%) will lead to a decrease in VO2 max of 10-27% with a corresponding drop in endurance capacity of 22-48%. In this situation blood volume is also reduced increasing its viscosity. Thicker blood is harder for the heart to pump and moves much slower through the circulatory system, resulting in less heat being lost from the skin and a rise in core temperature.


The kidneys regulate water balance very accurately during normal activity and strenuous exercise. After an indoor training session that produced a significant sweat rate, the kidneys will restore equilibrium in fluid balance within hours provided enough water is consumed. The kidneys achieve this rapid rate of rehydration via two hormones: Aldosterone which targets sodium and chloride balance and Anti Diuretic Hormone (ADH) that controls water balance.

Unless dehydration becomes extreme (exceeding 3% body weight) these two hormones work symbiotically to maintain hydration within 1% of normal limits. Knowing this, it is then logical to expect that the properties of urine will reflect whole body water status. That is: urine should be dilute and slightly opaque when there is an abundance of water within the body (hydrated). The opposite should be true when the body is conserving water (dehydrated) with urine being dark in colour and highly concentrated.

When evaporative cooling cannot take place - as covered in our previous blog - performance will deteriorate and your enjoyment of training will be diminished. If inappropriate clothing is worn for a ride then the evaporation of sweat is further reduced and core temperature will rise.

Finally, it is worth giving salt a mention. Salt is possibly the most important electrolyte. It is involved in the movement of water from the extracellular space to intracellular, nerve conduction and the maintenance of blood volume and blood pressure. Because Sodium is constantly being lost from the kidneys, GI tract and sweat glands its regulation is tightly controlled.

However the average daily diet provides enough sodium to meet the demands of exercise induced sweating. It is only when there is a departure from the normal exercise regime (such ultra marathon activity in a hot environment) that deficiencies appear. So supplementing salt is generally not required.

The following recommendations are based upon some of the complex physiological processes previously described and a fair amount of common sense. The aim is to make your indoor riding experience more comfortable and enjoyable.


  • Make sure you have a fan on when you train indoors and direct the airflow to your forehead and chest. Over half of the bodies sweat glands are located on the chest, back and forehead. If you have a high sweat rate it is a good idea to have a second fan located behind you and aimed at your upper back.
  • Most modern bib shorts and jerseys are breathable. However, leaving skin exposed to the air is ideal. For men wearing bib shorts with no shirt is an option and for women a sports bra under your bib shorts will be comfortable.
  • Try and encourage airflow within your indoor training room. Open any doors and windows 30 minutes before you start your ride and leave them open for the duration.
  • Stay hydrated at all times. Even on days where you are not planning to ride.


  • Armstrong, L.E. (2000). Performing in Extreme Environments. Champaign, IL. Human Kinetics
  • Ashcroft, F (2000). Life at the Extremes. Harper Collins, London.
  • Burke, L & Deakin, V. (2006). Clinical Sports Nutrition; 3rd Edition. Sydney. McGraw Hill

Also in Training

Indoor Bike Training: Benefits, Workouts & Plans
Indoor Bike Training: Benefits, Workouts & Plans

January 10, 2024 4 min read

Read More
Fitter for winter in 5 steps
Fitter for winter in 5 steps

October 18, 2023 2 min read

Training is tough, there’s no two ways about it. But getting started shouldn’t be – here’s 5 steps to making the most of your indoor riding this winter, and partner your training with the Wattbike Atom.
Read More
Ride the Tour de Wattbike with Alex Dowsett
Ride the Tour de Wattbike with Alex Dowsett

June 30, 2023 6 min read

Get ready to chase yellow with Pro Rider Alex Dowsett. 8 new workouts now on the Wattbike Hub.
Read More