Hey guys!

In this post 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. Let's go?

Sweating is an important body cooling mechanism in most sporting conditions. The most important thing you lose when you sweat is heat, you know? Sweating also results in fluid loss (which can result in dehydration), and along with this fluid we lose electrolytes (hence the salty taste of sweat). And obviously some athletes sweat a lot more than others – sweat rates can vary from almost nothing to 5 liters per hour!...

The most important factor in determining sweat loss is probably the amount of heat produced and this is dependent on the intensity of the exercise. The more energy we produce (the harder and harder our muscles contract), the more heat will be produced. For every kcal of energy produced, we will produce approximately 4kcal of heat.

The second factor is the climate. Hot, humid weather will increase your sweat rate. Another factor is the clothes you are wearing (which is why cool clothes are essential this summer). How trained you are and how accustomed you are to exercising in hot conditions are other factors. One factor that we cannot 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 may be one of the reasons why there are such large differences between individuals. That said, scientific literature suggests that it is not the number of sweat glands, but rather how well those sweat glands function, that is responsible for the differences between individuals.

“Gabi, how much liquid do we lose through sweating?” As I said, sweat loss can vary from person to person and from situation to situation. In a study of a very large number of athletes across a wide variety of sports, sweat rates were mapped – there were variations in sweat rates observed across different sports. The biggest highlight of fluid loss was in American football, where sweat rates are extremely high because the conditions are often extreme (hot weather), players wear a lot of protective clothing, have a lot of muscle mass and make explosive efforts, factors which means a lot of heat production. In other words, working with average sweat rates does not make sense and it is necessary to individualize each athlete.

The amount of sodium we lose depends on the sweat rate, duration of exercise and the concentration of sodium in sweat. If any of these are very low, the total losses are likely to be low as well. In a study by Barnes and others, the average sodium concentration in sweat was 36.1 mmol/L or 0.8 grams per liter. There was substantial variation, with some losing as little as 0.25 grams per liter/L and others up to 2 grams per liter.

The other electrolytes: Sodium and chloride are the two that have the highest concentrations in sweat and are the most lost. Potassium losses range between 160-320mg per liter of sweat and magnesium losses are only 4-15mg per liter of sweat. It is worth mentioning that the concentration of most electrolytes in sweat is always lower than the concentration in the blood – this is a way for the body to protect itself against hyponatremia.

So, dear readers, when you sweat during your workouts, remember that it's not just water that's leaving your body. Paying attention to sodium, magnesium and potassium loss may be key to optimizing your health and performance.

Thanks for reading and see you in the next post.

Gabi

References:

Barnes KA, Anderson ML, Stofan JR, Dalrymple KJ, Reimel AJ, Roberts TJ, Randell RK, Ungaro CT, Baker LB. Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: An update and analysis by sport. J Sports Sci. 2019 Oct;37(20):2356-2366.