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.
DEHYDRATION AND BODY TEMPERATURE Among the classical observations of the effects of dehydration is the finding that T,,rc during exercise in hot environments is increased to higher levels than T,,R in fully-hydrated subjects (Adolph et al., 1947; Pitts et al., 1944; Strydom and Holdsworth, 1968).
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 // 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. 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 // 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. 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 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. // 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.
“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.
Temperature regulation is a great example of how this works. If you go to the doctor at a hospital, the first thing they do is stick a thermometer in your mouth. They don’t even know why you’re there but they do that because the body temp is just that important. Our oral body temp is about 98.6°F. The core body temperature (rectum) is 99.6°F (usually done with babies.) What about the temperature on the surface of our skin? The air around us is almost always cooler than our bodies. Remember energy production is constantly generating heat,.
The temperature on the surface of our skin is usually about 10 degrees lower than our body. There are thermometers nowadays that could check the surface of your skin and correspond that to an oral temp. Daily (Diurnal) variations in body temperature Normally your body temp is highest at the end of your work day, about 7PM. Your body temperature starts to drop afterwards until you start to sleep and it continues to drop until a couple hours before you rise from sleep (about 4am). Why would the temperature be coolest a couple hours before you awake and not just before it? Because you have an internal clock in your brain that knows when you’re going to wake up and starts to speed metabolic activity up ahead of time.
If you go to sleep consistently, you will wake up at the same time, usually just before the alarm you have set due to this internal clock. Since we said your body temp is highest at the end of your work day What if you work the graveyard shift? Your body temperature is still going to highest at the end of your work day. So if you get off work at 2AM, it will be highest around then. Note the body temperature is lowest at 430am and highest in the afternoon.
Monthly variations in body temp in women In women specifically, there is a monthly variation that is affected by the menstrual cycle. During the latter two weeks of their menstrual cycle (during the postovulatory luteal phase), the increase in progesterone causes a 1°F rise in basal body temperature. The basal body temperature is the lowest body temperature during sleep. A woman could take their temperature every morning and the day they wake up and find that their temperature is one degree higher than the day before, then they know they are ovulating. This is cheaper than using an ovulation test kit. If a woman gets pregnant, their body temperature stays elevated for the entire 9 months because the progesterone stays at high levels to prevent menstruation from occurring.
Relevant: Three major sources of heat within the body 1. Cellular respiration is occurring in EVERY cell of your body. When glucose releases energy, more than half of the energy (60%!) is given off as heat which is why your body is nearly 100°F in temperature! Just like a light bulb that is fed with electricity, most of the energy is given off as heat instead of light.
Muscular activity generates heat for 2 reasons. (1) When you start to exercise or use your muscles, it increases cellular respiration to generate more ATP. (2) It also generates heat through something called “frictional heat” which is heat due to movement.
The same thing happens when you’re driving your car and the tires of your car get hot because they’re touching the asphalt. This doesn’t generate as much heat as cellular respiration when you’re resting, but it’s something. Ingestion of food.
The very process of digesting the food that you eat, absorbing the nutrients, and processing those nutrients generates heat. The metabolic rate increases 10-20% due to the energy “costs” of these reactions. It’s not only cell respiration but ALL biochemical reactions generate heat.
This effect, known as food-induced thermogenesis, is greatest after eating a high protein meal and is less after eating carbohydrates and lipids. Exercise may also increase the metabolic rate up to 15 times the basal rate (professional athletes may do up to 20 times).
Four major methods of heat loss from the body 1. Radiative heat loss from the skin. Heat flows from an area that’s warmer to an area that’s colder. That’s radiation and it’s just like (high pressure to lower pressure). Your body temperature is almost always cooler than the air around you. Only on the rarest of days in Los Angeles is the air around you warmer.
At 70F (21C), about 60% of heat loss occurs via radiation. If the air temperature was actually warmer than you, like say during a summer day in Las Vegas, then the heat would transfer onto you from the air. Cutaneous vasodilation. All blood vessels in the body are capable of dilating or restricting. Our body can affect or control how much blood flows through our cutaneous vessels (the vessels close to our skin).
If the vessel is dilated, that’s vasodilation. If it constricts, that’s vasoconstriction. When we’re hot, we could increase the rate at which we lose heat to the air by dilating the vessels, which means more hot blood flows through our skin and our skin will look flushed.
If you immerse your hands in hot water, the vessels dilate to get rid of the heat. Conversely, if we constrict the blood vessels, and reduce the amount of blood that’s flowing through our skin, that will reduce the amount of heat loss. If you put your hands in ice cold water, your hands will look white because of the vasoconstriction. Evaporation of sweat from the skin.
In order for sweat to work, the heat from your body has to cause the sweat from your body to evaporate. Let me give you an analogy, let’s say you put a pot of water on the stove and you turn on the flame. The heat from the flame is transferred to the water. As the water gains heat, the water molecules start to vibrate and move faster and faster and as they gain this kinetic energy, the water undergoes a phase change, going from liquid to a vapor/gas state. It takes energy to make something go from solid to liquid to gas. The water has gained enough energy for it to evaporate.
When we sweat, we release water onto our skin, the heat of our body transfers to our sweat and causes the sweat to undergo a phase change from liquid to vapor and we get rid of the sweat and heat at the same time. One factor slows this effectiveness of this: Humidity. The more humid the air, the slower the rate at which sweat evaporates. When you have 100% humidity, instead of water evaporating into the air, the water will condense and fall as rain. This is why most people can handle dry desert heat better than humid heat. Anywhere on the east-coast or the south in the summer feels like a steam room.
The sweat doesn’t evaporate and everything just rolls down and your clothes stick to you. Sweating only cools you down if the heat of your body causes that water to evaporate. If the air temperature is hotter than you AND it’s really humid, then it feels like you’re going to die (haha). Go ahead and exhale on your hand.
Feel how warm and humid it is? Every time we exhale, we lose water and heat from our body. About 20% of our body heat is lost due to exhaling. The lungs are the coolest parts of our body. Animals that cannot sweat, such as dogs, change their breathing pattern to get rid of heat and pant. If you have experience with a horse you’ll know that horses sweat and don’t pant.
Since we aren’t aware of this water loss through the skin and mucous membranes of the mouth and respiratory tract, it is called insensible water loss. The Thermoregulatory Reflex Center The temp control center is found in the. Whenever the body temp becomes lower or higher than the set point level, the TRC activates effectors to compensate and return the body temperature back to the set point level. The job of this TRC center is to regulate the body of the temperature at a set point of 98.6 degrees F. In order to do this it needs to get this information from thermoreceptors (through an afferent pathway) in the rest of our body. All the control center does is it COMPARES the actual body temperature with the desired body temperature.
If they match, the control center doesn’t have to do anything. If they don’t match, then its job is to get the temp back to the set point.
The TRC will send output signals across a motor pathway (an efferent pathway) to effectors such as cutaneous blood vessels, sweat glands, skeletal muscles (shivering) and glands (that secrete hormones that speed up cellular respiration). Remember the mnemonic: A comes before E in the alphabet, so signals are sent through an Afferent pathway (input) to the control center and then the output goes through an Efferent pathway to the effectors (muscles and glands).
Incidentally the analogy we’re going to draw from this is the thermostat in your home. If you have your thermostat set to 70, the actual temperature of your home will look like this above. The heater doesn’t turn on until it reaches a little bit below that. When it does turn on, it doesn’t turn off the moment it hits that set temperature. It will continue to blow heat a little above it. So the average temperature of your home is osculating at a “steady state.” This is show your body temperature works as well. What are the homeostatic reflexes that are activated whenever the body temperature is LOWER than the set point?
A) Person feels cold. When you’re colder than the set point, then you feel cold. Why do we say this?
Well, you’re not a dog. We have behavioral responses. Maybe you will put a sweater on or make yourself a hot drink or have some hot soup.
It’s not like you’re going to wait until you shiver. Or you might turn up the heat in your home. If that’s not sufficient or you don’t have a coat to put on, then the next thing that happens is b) Cutaneous vasoconstriction. When your blood vessels constrict, that reduces blood flow to the skin, minimizing heat loss. Incidentally you will tend to look pale because there’s less warm red blood flowing through your skin. If that’s not sufficient c) Shivering. Your skeletal muscles will be activated to constrict and that’s known as shivering.
All the above three things are activated by your nervous system. These are all caused by nerve impulses and happen very quickly. One quick point before we continue. The next time you’re shivering, you could stop shivering anytime you want. All you need to do is start moving. Start running in place, use your muscles, do jumping jacks, burpees, bodyweight squats, etc. You don’t have to keep telling yourself “I’m so cold, look at me, I’m so cold I’m shivering.” You could move your muscles voluntarily or involuntarily.
Luckily, your brain has built-in overrides to do it for you if you really don’t want to move, lol. D) Secretion of thyroxin and adrenalin. These involve the use of hormones. The nervous system works very quickly, it’s like sending e-mails electronically. The endocrine system is like sending snail mail. With hormones, you have to manufacture, secrete, and have them circulate in the blood stream to then finally cause changes in the body.
This may take hours in some regards. If you’re cold for an extended number of days, your thermostat in your brain will secrete thyroxin (from thyroid gland) and adrenalin (from adrenal gland) and both have very different purposes but they both increase the rate of cellular respiration to break food down at a faster rate, in part to produce heat. (We already learned that 60% of the cell respiration energy is given off as heat.) This is known as acclimatization.
In the winter time, as we are continuously exposed to cooler weather, and if you live in VERY cold places like Anchorage, Alaska, or Minneapolis, Minnesota, this is called “ Meat and Potatoes Country.” People eat heavy foods to keep up with the increase in metabolism. When the temperatures start to warm up, our metabolic rate slows down, we generate less heat. In the warm, summer months, people don’t feel like eating heavier foods and will choose the yogurt and salads because it gives off less heat. So that’s known as acclimatizing. What are the homeostatic reflexes that are activated whenever the body temperature is HIGHER than the set point? A) Person feels hot. Maybe you’ll take a jacket off, have a cold drink, and stand in front of a fridge.
If that’s not enough b Cutaneous vasodilation. The blood vessels will dilate to give off heat and the skin will look flushed. If that’s not enough c) Sweating. We will start to sweat to get rid of heat. D) Acclimatization.
Again, in terms of longer term acclimatization, our thyroid and adrenals will secrete less thyroxin and adrenalin to lower the metabolic rate. Next we take a pathophysiological application of this and talk about Inflammation and Fever! Basic Physiology Primers. Regulation of Body Temperature.