So, What’s the Ideal Body Temperature During Exercise?

There’s a reason the first few minutes of any workout feel the hardest. Whether you’re hiking through the woods, heading out on a trail run, or riding your mountain bike down the trail, your body needs some time to warm up.
When we’re not exercising—commuting to work, sitting at a desk—barely any of our blood flow is going to our skeletal muscles. Once we start exerting ourselves, though, the capillaries that bring blood to those muscles open up, and blood flow there increases dramatically. That’s when we’re really ready to perform.
Each body is different, but generally, when muscles are primed and ready to go, the body’s optimum core temperature falls within a specific range. It’s right around 37.5 degrees Celsius.

It’s even more important to take the time to warm up properly when it’s cold outside.
It’s even more important to take the time to warm up properly when it’s cold outside // U.S. Army Europe

“It’s important to know that your body temperature isn’t constant throughout the day,” says Dr. Greg Haggquist, founder of 37.5 Technology. Bodies are subject to circadian rhythm, a roughly 24-hour cycle that, as Dr. Haggquist puts it, “tells us when to go to sleep, when to wake up, and when we’ll perform our best.”
At night, when your body is resting, your core temperature might drop down to about 36.5 degrees Celsius. During the day, depending on what’s being asked of it, your body might raise its core temperature to 38 degrees Celsius.
This process, in which the body adjusts its temperature based on its surroundings and output, is called thermoregulation: the body’s ability to regulate that core temperature. Basically, says Dr. Haggquist, “your brain is making decisions about whether to warm your body up or cool it down.”

Shivering when it’s cold is one way your body burns calories to warm itself up.
Shivering when it’s cold is one way your body burns calories to warm itself up // boydechar

We’ve all experienced thermoregulation in action. To warm itself up, the body burns calories. This might include shivering, for example. Your body’s natural response when it’s too cold is to do those small, involuntary movements, which can burn a few hundred calories an hour. Hikers, skiers, and others who travel outside in cold weather often do jumping jacks or other movements to stay warm while they’re taking a break—it’s the same concept.
When conditions are warmer or you’re undergoing strenuous exercise, your body produces too much heat for comfort. In this case, thermoregulating might mean pumping blood to hands, feet, arms, head, etc., since moving blood to your skin away from the core helps you cool. If that doesn’t cut it, the body pumps liquid water into our skin pores (i.e. you sweat), which act as tiny evaporative air conditioning units to remove heat through the evaporative process. There, it becomes a vapor, much like boiling water on a stove.
“Heat loss is all about energy dissipation,” Dr. Haggquist explains. As a general rule, we lose about 580 calories per gram of liquid water the body evaporates—in a nutshell, that’s evaporative cooling from sweat. Humidity, too, plays a role in this process. High humidity reduces evaporation rates, reducing cooling, that’s why 85 degrees feels hotter in a humid climate than a dry one.
Comfort is the balance between heat loss and heat production, says Dr. Haggquist. That’s where 37.5 Technology comes in.
“If I’m running, only about 25 percent of the calories I’m burning go into running,” Dr. Haggquist explains. “The rest goes into heat production.” Each individual person has what he calls a self-fatigue point, a point at which your body says no. It won’t let you burn any more calories because it’s too hot. That’s when you can’t go any farther—when you “bonk,” as athletes often put it.
It’s that “bonk” point that 37.5 Technology helps athletes delay.
Ordinary wicking fabrics only start to work when our body’s cooling system breaks down. The liquid water comes out of our skin pores and spreads the liquid across the fabric with the intention of the fabric drying quickly. Not only does this mean the rest of our skin pores are now covered in liquid sweat making it harder for those pores to use the evaporative cooling process, says Dr. Haggquist, but by the time liquid sweat appears, those tiny A/C units have already failed.
“We approach the problem rather differently,” Dr. Haggquist says of 37.5 products. “We believe the humidity above that skin pore is the most important thing.”
Using tiny particles of either volcanic sand or coconut shell activated carbon that are embedded directly into the fibers, allow 37.5 fabrics to position at least 10,000 particles above the skin pore. Each of those particles act as desiccant—a sponge meant to attract and capture water. But, if all these fabrics did was absorb the water, your clothes would be completely soaked, so the idea is to capture moisture and to release it from the body and fabric.
“It’s a catch-and-release process that we’re doing,” Dr. Haggquist explains. “We catch the water molecule, then use the body’s infrared energy to release it from the clothing.”
And the technology works. In a blind study conducted by the University of Colorado’s Department of Integrative Physiology, athletes were asked to perform the same rigorous, hour-long workout on a stationary bike using three separate test cases: once with a standard wicking shirt, once with a shirt embedded with 37.5 technology, and once with a cooling vest and sleeves, which circulated cold water.

Fabrics made with 37.5 technology make it possible for athletes to maintain their optimal body temperature.
Fabrics made with 37.5 technology make it possible for athletes to maintain their optimal body temperature. // Bob Wick/Bureau of Land Management

Investigators measured each athlete’s core temperature while they were at their lactate threshold for 60 minutes. In the end, the study found that 37.5 fabrics had similar effects as a cooling vest, allowing athletes to go longer because their core temperature didn’t increase as fast compared to the wicking shirt.
Essentially, 37.5 fabrics made it possible for athletes to perform longer because their core temperature didn’t build as fast, and the researchers found that athletes were able to go 26% longer with the aid of 37.5 technology.
While it’s not practical for most athletes (elite or not) to wear a cooling vest, anyone can wear a shirt that uses 37.5 technology. In fact, the fabric is in many brands that you might already be familiar with: adidas, Katusha, Point6, Rab, Carhartt, and Salomon.
The results weren’t surprising to Dr. Haggquist. “37.5 technology responds to your needs,” he says. “It responds to your body’s needs—warm or cold—before you even know you need warming or cooling.” Now isn’t that cool.
Featured image provided by Informedmag