How much do you sweat and how much sodium do you lose?

Sweating is an important cooling mechanism in most sporting conditions. So the most important thing you lose when you sweat is heat! However, sweating also results in fluid losses (which can result in dehydration), and along with this loss of fluid we will lose electrolytes (hence the salty taste of sweat). It is also obvious that some athletes sweat a lot more than others. Sweat rates can vary from almost nothing to 5 litres per hour… In this article we will discuss what factors determine how much you sweat as well as what normal sweat rates are. We will also address electrolyte losses in sweat and in particular sodium losses.

Sport sweat rate infographic

What factors determine sweat loss?

The most important factor to determine sweat loss is probably the amount of heat produced and this is dependent on the exercise intensity. The more power we produce (the more and the forceful our muscles contract) the more heat will be produced. In fact, for every kcal of energy produced we will produce roughly 4kcal of heat. The second factor is the weather. Hot and humid weather will increase sweat rate. Another factor is of course clothing. How trained you are and how used you are to exercise in hot conditions are other factors. One factor we can’t influence is a genetic factor. We are born with a certain number of sweat glands and the exact number will vary from person to person. This could be one of the reasons why there are such large differences between individuals. Having said that the scientific literature seems to suggest that it is not the number of sweat glands, but mostly how well these sweat glands work, that is responsible for differences between individuals.

How much fluid do we lose through sweating?

As already mentioned, sweat losses may vary from person to person and situation to situation. In a study with a very large number of athletes in a wide variety of sports, sweat rates were mapped out (1). The infographic above shows the ranges in sweat rates observed in different sports (a rough reflection of the data obtained in the paper). The most obvious observation is the large variation within a sport. Another observation is that sweat rates in some sports can be extremely high. For example, in American football sweat rates are extremely high because the conditions are often extreme (hot weather), the players wear a lot of protective clothing, and the large muscle mass and explosive efforts means a lot of heat production.

The take home message here is that working with average sweat rates is meaningless. We really need to work out sweat rates of individual athletes. (In a previous blog we discussed how this can be done).

How much sodiu