How Much Do Cyclists Sweat?

Our bodies are made up of around 70% water. For a 70kg athlete, that equals nearly 49 litres of fluid!

This fluid plays a key role in a whole host of key physiology processes, from circulation to metabolism, that are vital for both maintaining health and performance.  

The loss of as little as 2% of body weight through sweat can negatively impact performance in certain circumstances. Sweat losses also contribute significantly to an athlete's daily fluid needs, meaning they are often many times higher than those of a sedentary individual. Therefore, knowing how much sweat a cyclist loses during a ride is an important metric when establishing how much to drink on a daily basis.

Whilst it would be convenient to provide athletes with a single figure for their fluid needs per day (e.g., 3 litres), this would be overly simplistic and, in some cases, potentially dangerous, particularly if it resulted in excess fluid intake during exercise which could lead to a serious condition called hyponatremia.

One key mechanism through which the body regulates temperature is through sweat. By producing sweat that sits on the skin and evaporates, we can lose a lot of heat through evaporative heat loss. This is a particularly important mechanism when we exercise in hot environments, where there is less of a gradient in which to lose heat, and we are producing more of it. 

The body is only around 20% efficient, with only around 20% of the energy we expend being used for producing power through the pedals and the rest being lost as waste heat.

When combined with hard riding on a hot day and without a sufficient sweat rate, core temperature will rise rapidly. As such, sweating is vital for maintaining a stable core body temperature. 

An individual athlete's sweat rates are influenced by a whole host of factors...

Exercise Intensity — The harder you ride, the more heat you produce, the more you sweat to help get rid of that heat.

Clothing—Clothing provides insulation, which further drives sweat rate as it becomes harder to lose that excess heat. The more insulative clothing, the greater the sweat rate. Due to the clothing worn, sweat rates can often be high, even when exercising in subzero temperatures in winter.

Body Composition—Fat provides insulation, which can be beneficial in the winter but can also influence our ability to dissipate heat and increase sweat rates in hot conditions.   

Exercise Duration – The longer we ride for, generally the lower the intensity that we can sustain, therefore the lower our sweat rate is likely to be. In contrast, shorter events allow for greater power outputs and therefore greater sweat rates.

Heat Acclimation – If you regularly train in the heat or are exposed to hot environments, one of the key adaptations to this exposure is an increase in your plasma volume (the water component of the blood), this can then increase sweat rate, meaning a heat acclimated athlete will sweat more than a non-heat acclimated athlete. 

Environmental Temperature – The hotter the environment, the less of a gradient the body has to lose heat, and the more you are likely to sweat. 

One of the highest rates of sweat loss during exercise ever reported in the scientific literature was from the Olympic runner Alberto Salazar, who, over a 134-minute marathon, produced sweat at a phenomenal rate of 3.71 litres per hour. This resulted in over 5kg of body weight loss! I've also personally witnessed a sweat rate of 2.7 litres per hour with a heat-accommodated runner on a treadmill in an environmental chamber with no cooling at around 40oc. Alberto was a relatively small individual at 67kg and sweat rates as high as 5 litres an hour have been reported in highly trained larger individuals! 

As cyclists, we benefit from the higher speeds compared to running, which help support convective heat loss through the greater movement of air over the skin's surface, helping to assist cooling and allowing greater power outputs. 

Based on lab data collected from over 1300 athletes of different sports, the typical sweat rates seen in cyclists range from 0.5 - 1.5 litres per hour, which makes rehydration on the bike to limit losses more realistic, given that fluid intakes above 1litre per hour are often not practical or tolerable in most athletes. 

Within Fuel The Ride Academy we cover in detail how to measure your own sweat rate, and how to develop you own individualised hydration plan based on this. 

Coach Ben