If you’ve ever wondered why you’re always drenched in sweat at the end of a boot camp class while your friend is barely glistening, fret not. Your heavy sweating could be a sign that you’re physically fit.
Research shows that fit individuals, especially those who train for endurance sports like running and cycling, sweat sooner and more profusely than people who rarely get physical.
The primary purpose of sweat is to cool the surface of the skin, which helps to regulate body temperature, explained Dr. Carolyn Dean of the Nutritional Magnesium Association.
“Sweat is one of the main ways of preventing your core temperature from climbing to dangerous or harmful levels,” she said.
The process goes like this: When you overheat, your body signals its sweat (eccrine) glands to start producing sweat on the surface of the skin. As the sweat droplets heat up, some of the sweat evaporates, effectively dissipating heat and leaving behind cooler liquid sweat.
As we move, the air around us works to cool the remaining water on our skin.
“When you’re fit, you’re able to work harder, generate more power, and sustain that power for longer time periods,” said Dean. “Most of this power output generates heat, [which] means you [can] generate a lot of heat in a very short period of time and for a longer duration.”
In other words, fit people sweat sooner and more because they develop a faster response that reduces their core body temperature as they heat up, said physical therapist and strength trainer William P. Kelley.
“Your body gets better at reacting to the increase in temperature, and [thus] begins cooling you sooner and more efficiently, so you can maintain a greater workload for a greater period of time,” he said.
People who have a low level of fitness, on the other hand, may stay drier during workouts than people with a higher level of fitness because they haven’t trained their bodies to recognize a high energy output and subsequently initiate the proper cooling response.
This isn’t a hard and fast rule, though: How much you sweat during any given workout depends on the amount of energy you’re exerting.
Regardless of your fitness level, if you’re exercising at an intense rate that pushes you close to your VO2 max (or maximal oxygen consumption), “the more heat you’ll create and the more you’ll sweat,” said Dean.
Therefore, someone who is less fit may start sweating sooner than a trained athlete when doing the same workout at the same pace (like running for 20 minutes at 10 minutes per mile). In effect, the less-fit person would have to exert more energy than a trained athlete would to complete the same exercise, and would thus reach their VO2 max much earlier, causing them to sweat more quickly.
If, on the other hand, a fit person and an unfit person are each working out to their individual VO2 max (let’s say that means 8 minutes per mile for the fit person and 10 minutes per mile for the less-fit person), logic follows that the fit person would sweat sooner because their body is more efficient at lowering their core temp.
“[How much you sweat] is an important characteristic to learn about yourself to optimize physical performance and prevent heat illness.”
- Dr. Robert Sallis
Another factor that influences sweating is body mass. Someone with a higher body mass has to work harder to perform the same task as someone with a lower body mass, Kelley explains. The greater energy exertion effectively raises that person’s body temperature and causes them to sweat more.
Dean also said overweight individuals can produce a lot of sweat from very low activity levels, like climbing a flight of stairs or taking a short walk.
“The core temperature of obese people is higher because fat acts as an insulator, so they sweat more to try to cool down,” she said.
Environmental factors also contribute to your sweat level ― anyone who has gone jogging in a humid climate can attest to that.
“The higher the humidity, the greater the water vapor density already in the air, so more sweating needs to occur in order to get an adequate amount of evaporation for body cooling,” said Kelley.
High temperatures only contribute to the problem, he added, since hot air can’t cool the sweat on your skin as quickly as chilly air can.
A dip in blood sugar level can also lead to greater sweat levels, according to Dean.
“When blood sugar levels drop below normal, your adrenaline and norepinephrine kick in (fight or flight response), which causes sweating while exercising or at rest,” she said.
Fitness, body type and environmental reasons aside, there are myriad other factors that drive sweat rates. Dean says sweating can be a reaction to drinking alcohol or coffee, wearing restrictive synthetic clothing, or taking certain medications that affect your ability to tolerate heat. Other factors might include dehydration, menopausal hot flashes, an overactive thyroid gland, genetics, nerve issues or disorders, and skin diseases.
“[How much you sweat] is an important characteristic to learn about yourself to optimize physical performance and prevent heat illness,” said Dr. Robert Sallis, co-director of the Kaiser Permanente Sports Medicine Fellowship Program at Fontana Medical Center.
The important thing to remember? Replace sweat with water and electrolytes.
You can roughly calculate your sweat rate by weighing yourself before and after you workout (aim for 30 minutes to one hour of high-intensity exercise). A good rule of thumb is to drink 16 ounces of fluid for every hour you exercise if you lose about a pound after a gym session.
If you plan to exercise in hot or humid conditions, Sallis said, you need to know how much water to drink to avoid dehydration. If you can, break your fluid intake into smaller segments (like four ounces every 15 minutes) to stay hydrated early on, advised Sallis.
Clarification: This article has been updated to make Sallis’ statement about drinking water more clear.