Knowing how much you sweat is important to proper hydration. An athlete's sweat rate typically ranges from about 0.5 to 2.0 L/h, or about 17 to 68 oz/h, but it can be as high as 3.0 L/h, or 101 oz/h, in rare occurrences. Sweat rate is influenced by the athletes hydration status pre workout and also by the climate. It can change from season to season depending on training efforts and other factors.
Here is how it works:
Sweat Rate (L) = [Body Weight Before Exercise – (Body Weight After Exercise – Fluid Intake During Exercise + Urine Output During Exercise)]
There are a few things to note to be sure you get a more accurate measurement:
Athletes should use the bathroom before they are weighted pre exercise.
Athletes should be weighed either with minimal clothing, usually compression shorts for males and shorts and sport bra for females.
Fluid, water or sports drinks, and any food should be monitored and tracked during exercise.
If athletes need to urinate during exercise, they can be given a pre-weighed container and asked to collect all urine for weighing. If athletes need to have a bowel movement during the test, they can be weighed again before and after going to the bathroom to determine stool mass loss.
After exercise, athletes will towel-dry themselves and be weighed with the same scale and wear the same clothes as the before exercise body weight measurement.
There is not a fool proof way to measure exact sweat rate, but this equation can give you a good sense of how much you are sweating out. Electrolyte loss is another consideration, and I will discuss that in another blog.