Science Friday: Embrace the Heat

It’s mid-July. It’s hot. It’s humid. It’s horrible.

Running in the heat is miserable, as I’ve experienced in a few races and every time summer rolls around. As you heat up, your heart starts beating faster to pump more blood to the skin, where the heat can be released. Sweat rate increases to help cool the skin through evaporation. (The reason humidity is such a nuisance is that the air is so saturated with moisture, the moisture on your skin doesn’t have anywhere to go and the cooling effect of sweat is lost.) Running performance plummets because your heart is working harder than usual, but the oxygen-rich blood is being shipped to the skin, not to your muscles. In addition, sweating can lead to dehydration and electrolyte loss.

Every summer we are reminded what to do to exercise safely: run in the shade, early in the morning, in technical clothes (Dri-fit, etc.); drink water and/or electrolyte beverages before, after, and possibly during runs; and accept slower times or even a workout cut short. We are comforted that after a few weeks (about two), things will get better. Our bodies will adapt by sweating sooner, more aggressively, and forfeiting less salt (yes, being super sweaty is a good thing). The heat won’t annihilate our workouts as much; we’ll be able to go faster with less effort and lower heart rates. We’ll be acclimated.

Yes, a couple weeks in the heat means it’s less terrible to be in the heat. But this news is not preventing me from daydreaming of moving to Antarctica. What does hot weather training have to offer, besides a pile of drenched clothes and a sports bra tan line?

A 2010 study by Santiago Lorenzo and colleagues details an unexpected reward. In the study, competitive cyclists were split into two groups. At the start, both groups endured a number of physiological tests in both cool (55°) and warm (100°) conditions. One group then spent ten sessions riding at an easy pace in a hot room (104°, aka too hot to try this at home) while the other group did the same workouts in a cool room (55°, aka ideal exercising weather). After the ten sessions, both groups were again tested in cool and warm conditions.

A summary of the results is shown in the graph below. As you’d expect, when tested in the heat (black bars) the experimental group that practiced in the heat improved across the board: increased VO2max (the maximal amount of oxygen that can be taken in and used), lactate threshold (the point above which lactate accumulates in the blood; approximately tempo run pace), Qcmax (the maximal cardiac output, how much blood the heart is pumping), and time trial performance. They were acclimated after the ten sessions. The control group that practiced in the cool room was not acclimated to the heat, and the group's scores hovered around zero; they didn’t improve much from the start to the end of the study. Not surprisingly, their time trial performance worsened in the heat.

What was surprising to the researchers were the results from the tests in the cool conditions (white bars). Even under these conditions, the group that practiced in the heat did much better compared to the group that practiced at ideal temperatures. Again, both physiological measures and performance improved in the heat-acclimated group while the cool-training group remained the same. Heat training led to improvements no matter the conditions.

As Steve Magness mentions in his new book The Science of Running, heat training is analogous to altitude training. The stresses our bodies have to deal with in the heat (less blood flow and oxygen to the muscles, similar to training at high altitude) force a number of adaptations, including increased blood volume. In the summer, you get an “altitude-like effect” without having to move to Flagstaff or Mammoth Lakes. (And it might even discourage dreams of Antarctica.) When the weather cools, your body will be stronger and tougher from its heat training.

So embrace the heat (safely). Come September, you might have a shiny new PR because of it.

Dream big and don’t sweat the sweating,

Teal