“Work is the inside made into the outside.” - David Whyte
In 1984, a graduate student by the name of David Carrier published a paper that described an ancient method of hunting practiced by early humans, one that was, in many ways, quite crude. Described as persistence hunting, Carrier explained how human runners tracked and pursued their prey for miles, sometimes for days, chasing the animal until it was worn out. Antelopes and other sources of human protein could run very fast, but only for short distances. Humans weren’t as fast, but could run for long distances with very little rest. Our ancestors stalked their prey until it collapsed from sheer exhaustion, throwing rocks at the animal until it was dead. Carrier proposed that, although early humans were not the fastest runners nor the most cunning of hunters, we utilized a uniquely human physical characteristic that other animals lack—we are very good at sweating.
Any physical activity that works the muscles at an intense level of effort, such as running, generates a considerable amount of heat, which becomes dangerous when the body does not have the ability to cool itself down. Antelopes, wildebeests, rabbits, and other prey may be super speedy, but they do not have the numerous sweat glands found on the human body. Many animals that run long distances take advantage of panting, which is not very efficient, especially when the animal is running. But humans have sweat glands all over the body, which provides numerous outlets to get rid of body heat via water droplets.
There are numerous reasons why we sweat, including anxiety, fevers, humidity, hormones, and some medical conditions. Most of us don’t enjoy sweating under these conditions, especially in public when a drenching from excessive perspiration makes us self-conscious. Sweating during exercise, however, is a different process, one that is amazingly delicate and plays an important role in keeping us alive.
Humans are homeothermic, which is a fancy way of saying that our body carefully regulates its internal temperature, keeping it within a very narrow range of about 3 degrees, between 97 to 100 degrees Fahrenheit. The hypothalamus acts as our thermostat, constantly monitoring our internal temperature, accelerating heat loss when the internal temperature rises and producing heat (via shivering) when our temperature gets too low. Additional information about our internal temperature comes from areas located throughout the body via sensory receptors called thermoreceptors. The hypothalamus also receives information from other parts of the brain as well as the spinal cord. We have peripheral receptors in the skin that relay information about the skin’s temperature and the external environment surrounding it. These receptors not only relay information to the hypothalamus but to other areas of the brain that may not directly regulate our core temperature but are involved in our perception of whether we are hot or cold. These receptors enable us to make minor changes long before our core temperature becomes dysregulated; they are what trigger that “itchy”, uncomfortable feeling that spurs us to take off a jacket or turn on a fan before we start to sweat.
When skeletal muscles move they generate heat. How much heat is produced depends on how many muscles are engaged for a given activity and the amount of force produced. Unless we can effectively dump excess body heat, our core temperature rises beyond its ideal range. The shift in temperature causes the sympathetic nervous system to activate our sweat glands, which releases the excess heat in the form of water. The droplets form on the surface of the skin and, ideally, are whisked away by wind or evaporation. On a humid day, it takes longer for the sweat to evaporate, making it much harder to keep our core temperature within a safe range.
Cooling is the primary function of sweating--without it we would have no way to release heat and regulate our body temperature--but it is the evaporation of the water away from the skin that is important, not the sweat itself. That is why exercising in hot and humid environments increases the risk for dehydration and heat exhaustion—the “wet” air makes it harder for the sweat to evaporate. It is also why moisture wicking clothing, fans, and air conditioning are important tools to keep us cool during exercise.
From a physiological perspective, sweating during exercise is an essential and healthy process. Compared to other body processes, such as metabolism and blood glucose regulation, sweating is simple and straightforward: the hypothalamus senses that the core temperature is rising and the body responds by stimulating the sweat glands to release the heat in the form of water droplets. But this simple system is frequently credited with a number of benefits which it does not provide, and embellishing what it can do frequently leads to some dangerous health consequences.
Sweating is commonly associated with weight loss. If you step on a scale before and after a sweaty workout you may be pleasantly surprised by a loss—sometimes as much as two or three pounds. Before you do a happy dance, keep in mind that what the scale is measuring is water loss, not fat. Within a few hours or perhaps a day, that weight will return as your body rehydrates. Our metabolisms are quite complicated, and the role of exercise in weight loss is still unclear. Recent studies that use more precise data collection tools show that exercise, although extremely beneficial for our health, plays a relatively minor role in weight loss, but is critically important for supporting our health. The scale is not an accurate reflection of the value of a workout; a two or three pound water loss can potentially lead to poor food choices post workout.
The importance of sweating during exercise extends well beyond weight loss. It is a measure of how hard we are working and can be a reflection of how fit we are. First, provided it is not excessively humid and there is good airflow, sweating during exercise is an indication that our muscles are working at an intensity that is beneficial to our overall health. Exercising at moderate to high intensities—the types of workouts that create sweat--has been shown to regulate blood glucose, strengthen the heart, improve sleep, regulate appetite, and reduce stress as well as inflammation. Importantly, the benefits come from the work that creates the sweat, not the sweating itself.
Secondly, although there is a great deal of variation in how much and how quickly people sweat while exercising, there is evidence that our sweating becomes more efficient as our fitness improves. In addition to supplying oxygen to the working muscles, the cardiovascular system must work harder when our core temperature starts to rise; our heart rate increases to pump more blood as the smooth muscles of the blood vessels dilate. As our cardiovascular health improves we develop more capillaries, which improves our ability to cool off by sweating earlier in the workout. These adaptations that are related to fitness make us more likely to sweat earlier in our workouts and more efficiently, allowing us to work harder for longer periods of time.
Some wrongly believe that sweating during exercise releases endorphins, leading to that “feel good” sensation we get after a hard workout. Again, sweating has one job—to cool us down. Like weight loss, it is not the sweating that stimulates endorphin release, but the intensity of the exercise that causes us to sweat. Endorphins are released in response to exercise intensity and length; the harder and longer you exercise, the more endorphins are released. There are some studies of Finnish men who spend time sweating in saunas that show improvements in mood, but the studies emphasize that improvements are more likely due to the activity itself, not the sweating. The benefits of sitting in a sauna are associated with heat-induced stress relief and the possible positive effect on the heart, which must work harder when in hot environments. How long these benefits last compared to exercise is not yet known.
One persistent myth about sweating is that it helps to release toxins. In our wellness infused and germophobic culture, we are strongly attracted to anything that purifies the body. Most people’s sweat contains a very small, if not miniscule, amount of toxins. Sweat is mostly water, with small amounts of sodium, potassium, calcium, and magnesium, all of which are electrolytes that play a role in various nervous system functions, such as flexing muscles. The loss of these electrolytes during a sweaty workout can lead to that feeling of “hitting the wall” when our performance deteriorates over time. Aside from water and small amounts of electrolytes, we also excrete pheromones and bacteria in sweat, which can make us stink. Sweat can also contain miniscule levels of heavy metals and BPA plastics, but the liver and kidneys do most of the work in removing these toxins.
Misconceptions related to the unfounded benefits of sweating can lead to dangerous behaviors, such as wearing a sauna suit designed to increase body heat and promote sweating while exercising. Unfortunately, most of these products are wrongly promoted as weight loss tools. I had to rescue a woman in one of these suits from a treadmill when she became dangerously overheated while running and almost passed out. She was seriously dehydrated and had to be transported to the hospital for heat exhaustion.
Rather than getting lured into false claims of narrowed waistlines and released toxins, we should appreciate sweating for the one thing it does very well—it cools us down. Looking back throughout history, it was sweating that helped us evolve into the sophisticated and complex species we are today. Sweating enabled us to keep moving when other species dropped with exhaustion; without it, we would never have gotten enough protein to feed our growing brains, which helped us develop better hunting tools, learn to build fires, cultivate crops, and eventually invent ultra processed foods and Tic Tok. Well, we may not want to go that far in our appreciation, but the next time you feel those beads of perspiration along your hairline or down your back as you work out, thank your body for the pretty amazing ways it helps to keep us moving, working hard, and functioning well.
👍🏻😊