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Does Fatigue Increase the Risk of Hypothermia?

I have been doing many stupid things in the name of science for 30 years now as a student and scientist in environmental physiology. In this article, I’ll focus on two of my stupidest things.

We know that winter cycling can be a chilly experience, but if you get tired from long distances / hard rides, can you be at increased risk of hypothermia?

Extreme weather requires additional planning to make your rides and workouts fun and safe. The challenge when it’s cold is to maintain body temperature. This can be difficult with a combination of cold temperatures and wind chills from high speed driving.

The two keys to maintaining body temperature are exercise intensity along with clothing. If you’re protected from the wind, you can get away with fairly light clothing if you work hard in the woods of a fat bike at low speeds. However, if you are traveling on exposed roads at fairly high speeds, you will need more clothing.

But what if I get tired while riding? Is there an increased risk of hypothermia? In this video, we’ll look at one study in which people were exposed to a cold after five hours of strenuous exercise, and another in which participants quivered for 24 hours in a row.

Check out the full video below!

Video transcript

The cold can be a harsh and relentless environment for survival and prosperity. In addition to clothing, fire and shelter, the body’s main way to prevent hypothermia in the short term is to generate its own fever, primarily through tremors.

In today’s episode, we’ll see if the tremor can last indefinitely, or if the tremor gets tired, especially when the body is tired from prolonged exercise and lack of food.

We go into the time machine, see a classic study by Peter Tikuisis, and partner with it in a more recent study I did. These two are the most unpleasant studies I have personally participated in throughout my 30-year career. The basic question is whether extreme fatigue and inadequate nutrition from strenuous exercise can cause tremors to suffer. For long periods of exercise in a heat-neutral environment, we usually rely on carbohydrates, which are either glycogen stored in the body or carbohydrates eaten during exercise. This is also true in the case of intense tremors. Therefore, low carbs can reduce tremors. It may also be because your muscles are tired from long hours of exercise and you can’t generate that much power.

So, in 1999, Tikuisis tested cold hardiness after 5 hours of various intense exercises that combined three types of aerobic exercise, boating, jogging, and cycling with heavy weight training. During this time, only water was allowed, no food was allowed. Next, I was exposed to a cold, windy shower for up to 4 hours. It consists of taking a 10 ° C shower and wearing shorts in a 10 ° C room, all with a wind of 6 km / h. Yes, this was certainly terrible enough to hear it! Of course, there was also a control condition, usually feeding in advance and not exercising for 5 hours.

These two graphs show the main story of this rewarding study. On the left is the well-named “Survival Curve”, which shows the number of participants remaining for the four hours. As shown by the dashed line, fatigue tended to result in faster dropouts and shorter permissible times, which was not statistically significant. The graph on the right shows the individual responses of the 13 participants during the control trial, highlighting the large inter-individual variability in response to the same cold stress. The thin, medium, and thick lines represent lean, medium, and high body thickness, respectively. The big difference was in the tremor rate, which had nothing to do with aerobic fitness or body fat. Indeed, as you can see in this graph, some lean people had strong cold resistance, while some high-fat people were only in the middle of the cold-resistant road. Predicting individual tremor drives and cold resistance remains largely a mystery to this day. Interestingly, I had a moderate body fat and moderate hardiness response in Participant # 9. Another interesting finding was the apparent change in fatigue testing that was more dependent on fat metabolism, and the idea that tremor was an inflexible process that relied solely on high carbohydrate utilization. Revealed.

In 2016, we followed up on this question in another very rewarding survey. In this study, eight participants combined minimal clothing with 7.5 ° C air to sustain a moderate tremor for 24 hours. They were given normal calories because they were simulating Arctic survival, but they were viable and had only 0.5 liters of water. The dashed line shows that heat generation persisted and actually rose slightly over 24 hours. Shadowed graphs, on the other hand, show that within 6-12 hours after exposure, the body appears to be naturally transitioning to become more dependent on fat metabolism. Overall, these studies are good news for extreme survival situations, suggesting that tremors and heat production can be sustained for at least 5 hours without strenuous exercise and food, or 24 hours without exercise and adequate food. This is important information for both military planners and search and rescue survival modeling.

I hope this research into the fascinating world of environmental physiology does not give you a cold shoulder.

Giro snow

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