Recall last week we learned that each and every one of us will have a reduction in our endurance performance in hot temperatures. But before we venture into strategies to reduce its effect (there are many) it's important to understand why we go slower. When we understand why, it reveals where we can go to lessen its effect.

A bit more about the Tatterson study. In the hot trial, the cyclists were sweating more. And their skin was warmer. What was the same however (and this is where it gets interesting) was the core (rectal) temperature. To be clear, whether they were performing in hot or cool temperatures, going all out to get their best times, core temperature was the same. It was almost like the core temperature was acting as a key governor of the performance.

Energy transfer

So why might the body care about its core temperature?

To start to understand, we first need to consider some basics about energy. We probably have heard about the first law of thermodynamics: “Energy cannot be created nor destroyed. It is transformed from one form to another”. For example, when we ingest food, we convert its stored energy into mechanical energy and heat. The conversion of that energy is pretty inefficient. When we exercise, only around 20% of the chemical energy breakdown from food contributes to mechanical work of movement. That inefficiency serves an important purpose. It works to keep us warm. But in the exercise situation, where we’re really ramping up the food => mechanical energy conversion, you can see the problem. We get too hot.

Why is getting too hot a bad thing?

The simple answer — we are made of protein. And in our protein-based engines, if the body temperature goes beyond a certain level, our proteins become “cooked” and lose their function. We can die.

To visualize the issue, think about how an egg changes its appearance as it's being fried. Your body’s job is to protect such an occurrence from happening in you.
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Fortunately, before we get to the fried egg situation, there is very strong feedback to the brain to say — stop or slow down. Take a look at the expression on my face at the end of a hot and humid Singapore 70.3 triathlon event where we were running a heat study. My core temperature (from a pill I swallowed) was 39.3 degrees Celsius. Bordering on too hot.
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When I read David’s findings, I realize that our body is a wonderful self-regulated machine! Following the first rule of thermodynamics, cyclists who exercised in a hot environment had to protect their proteins from “cooking”. Their nervous systems did so by 1) diverting the blood to the skin, 2) making more sweat and 3) subconsciously lowering their pace. That means high-intensity performance is greatly influenced by factors related to body temperature rather than simply being dictated by the power of your metabolic protein-based engine. The various happenings of this system are summarized here.

Great. So we're clear that protection of our core temperature within a tight range is another critical factor when it comes to performance. But how hot is too hot? Where is the sweet spot of temperature we can handle? And how can we move the needle when we want to perform better in these hot temperatures?​
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We'll continue the journey next week.

Class dismissed,

Paul Laursen, PhD

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