Extreme Body-Core Temperatures

Marines submerge themselves into a frozen pond.
U.S. Marines fully submerge themselves into the water of a frozen pond at the Marine Corps Mountain Warfare Training Center, California, on Feb. 2, 2021. (Lance Cpl. Andrew R. Bray/U.S. Marine Corps photo)

On the National Geographic Channel Fight Science-Special Ops episode, you will see the effects of body-core temperature in both extremes and how science manages them both. By definition:

Hyperthermia: Abnormally high body temperature due to exposure to extreme temperatures, high humidity and heavy workloads. Heat-related injuries are more common than ever now because of high levels of exertion in desert combat areas with heavy protective gear. In the extreme, hyperthermia can result in heatstroke, which is potentially fatal.

Hypothermia: Abnormally low body temperature resulting from excessive heat loss due to cold exposure. Hypothermia leads to a rapid degradation of operational ability cognitively and physically.

The most significant factor in limiting muscular performance during prolonged, high-level work probably is the buildup of heat in the muscles and body core. A device called Core Control (http://www.avacore.com/) that can get this heat out of the body as efficiently as possible has been researched and developed by Stanford University physiologists Craig Heller and Dennis Grahn. It may be a year or so before a usable model is on the market, but you will see on Fight Science that the current stationary model works quickly.

I was the guinea pig testing this device after cold-water exposure and during maximal performance workouts, where I produced excessive body heat that would have affected my performance if I did not have the benefit of accelerated cooling during brief rest periods.

Here is the workout I did on the show to induce hyperthermia:

  • Maximum pull-ups: I did 29 until I failed, and then with no rest
  • Max push-ups in one minute (70) and then with no rest
  • Max abs in one minute (50), and then with no rest
  • Ran on a treadmill for 90 secs (a quarter-mile)

Then I rested three minutes with the AvaCore device on my hands to cool my body.

I repeated this cycle five times with some decreases in performance, but I still totaled 120 pull-ups in five sets, which I never have done. Usually, without the cooling, I get 100 pull-ups on a good day in five sets without adding the run portion.

(This workout is a great workout to help push your maximum PT scores. Many folks who do this one can go from 10-15 pull-ups to 25-30 pull-ups in a few months, if done only once a week) Workouts like these and others are located at the Military.com Fitness Center eBook Store.

Here are a few questions I asked Heller about how we can utilize this science during regular training sessions and physical fitness test:

Military.com: Can you rewarm using cups of hot water in hands? The reason I ask is because I remember during Hell Week at SEAL training, when we ate inside, we all would get warm water and wrap our hands around it, and it seemed to help .

Heller: "Yes, but its effectiveness is limited. When you are cold, you are tightly vasoconstricted. If the cup is hot enough, it will cause a reflex vasodilation, and therefore heat will be transferred. Once the contents of the cup is cool enough to drink, it is best to drink it and get all of the heat inside. What the vacuum of the Core Control does is to facilitate the vasodilation. The vacuum in itself cannot induce the vasodilation, so the warm/hot stimulus is necessary, but once the vessels are dilated, the vacuum dramatically increases the heat flow."

Military.com: Can the same approach be used in the reverse? Say using ice-water bottles in your hands during rest periods, or would the constriction be so much that it would be useless? Are there some results using cold ice-water bottles?

Heller: "Most of what we currently do with Core Control is enhance heat loss and cool people down. Someone who is overheated because of working in the heat is already vasodilated and losing heat from the hands. Contact with a cold surface will facilitate that. However, if the surface is too cold, there will be a reflex vasoconstriction, which will stop effective heat exchange. The vacuum seems to lower the threshold for vasoconstriction so that the vessels remain open to lower temperatures and amplifies the blood flow through these vessels, thus enhancing heat loss. We have recently completed a study in which we have compared the maximum heat-loss capacity of different skin surfaces, and the palms are about 10 times other surfaces per area."

Military.com: The reason I ask is that I tried this a few times, and last summer one of my guys successfully ran the Chicago Marathon, using cold bottles on his hands while running when many runners were suffering from heat illness and even heatstroke. Do you think holding the cold bottles helped?

Heller: "Yes, for sure it would help. Of course, he would have gotten more benefit from the cold bottle by drinking it, as then none of the cold would have been wasted on the hot environment. However, drinking too much during a marathon can be dangerous. You need to replace water loss, but this is not easy to do by massive drinking, as the rate of absorption from the gut is limited.

"When you are exercising hard, the blood flow to the gut is diminished. There are frequent cases in which people have consumed lots of water during marathons, and when they stop, all of a sudden, there is massive absorption of the water that is in their stomachs. This can dilute the blood to the extent that they pass out and even die." Related article: Can You Die If You Drink Too Much Water?

Military.com: I am trying to show people that, as you have discovered, special blood vessels in the palms, the soles and the face are the body's natural heat exchangers. The CoreControl device optimizes these natural heat-exchange adaptations, but aren't there common experiences in which we use these special avenues of body warming or cooling?

Heller: "Sure, there are many common experiences that illustrate the effectiveness of our natural radiators. When you are cold and approach an open fire, what do you do? You hold out your hands. If you don't have a fire, you might rub them together vigorously to produce heat by friction. Or, as you mentioned, you grasp a very hot cup of hot chocolate, tea or coffee between your palms.

"In the heat, remember how good it feels to dangle your feet in water or take Grandma's advice to run cool tap water over your wrists. You can also put a cool towel on your face. Without thinking, we exploit the special heat-loss blood vessels in the palms of our hands, the soles of our feet and the face."

Stew Smith is a former Navy SEAL and fitness author certified as a Strength and Conditioning Specialist (CSCS) with the National Strength and Conditioning Association. Visit his Fitness eBook store if you’re looking to start a workout program to create a healthy lifestyle. Send your fitness questions to stew@stewsmith.com.

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