IIt's like common sense: If you leave a fitness class looking like you just rode down a log chute, you've probably worked harder than if you were barely shining. But that's not always the case, says Adam Collins, a researcher at the University of Bath's Center for Nutrition, Exercise and Metabolism.
According to him, sweating is part of the process of thermoregulation. When your body temperature rises, it signals your brain to sweat to cool down. As sweat evaporates, it helps regulate body temperature.
One of the reasons for the rise in temperature is physical activity. “When we exercise, the energy we produce to fuel that activity creates heat as a byproduct,” says Collins. The more intense the workout, the more heat is generated—and generally, the more you sweat. But sweat levels can be misleading.
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“There are many other factors that influence how much you sweat,” he adds. These include the temperature of the environment, your clothing and humidity. In humid conditions, sweat evaporates less efficiently, making you feel sweatier than usual, whether you're working hard or not.
“If you were to go for a light jog on a hot, humid day, you'd probably be sweating a lot,” he says. “But on a cold day, you can run at a much higher intensity and hardly sweat.”
Sweat also varies from person to person. Your fitness level, age, gender, body size, and even whether you're acclimatized to the climate you're in all play a role.
So no, sweat is not a reliable indicator of how hard you've trained. The best indicators of exertion include the intensity of your breathing, your perceived effort, and your heart rate, which you can track using a chest monitor or smartwatch. However, “sweat is a good indicator of dehydration,” Collins says. So if you come out of your workout wet, you'll need to drink.
