As anyone who has ever gone for a run on a sweltering July day knows, working out in the heat and humidity can put a dent in your mood and energy level, not to mention turn you into a drippy, sweaty mess.
Now, research from the University of Nebraska at Omaha suggests another consequence of exercising outside when temperatures are high: it can affect your muscles on a cellular level and do a number on your performance.
These preliminary findings are part of some pretty fascinating research happening at UNO’s School of Health and Kinesiology. There, researchers are studying how training in different climates can affect your muscles. More specifically, they’re looking at how mitochondria—the power generators in your cells—are influenced by various temperatures, Dustin Slivka, PhD, head researcher and director of the Exercise Physiology Laboratory at UNO, tells Health.
Why is this important? Mitochondrial dysfunction plays a major role in obesity, , aging, and other conditions. Slivka and his team want to find out what the optimal temperature is for working out, which might prevent this dysfunction and potentially lower rates of disease.
“If we can further optimize the outcomes of physical exercise then we can better combat these disabilities,” Slivka says.
In one ongoing experiment with 36 participants, the researchers have been extracting muscle tissue samples from each participant’s thigh before, immediately after, and three to four hours after they’ve completed an hour of cycling in a climate-controlled chamber. Temperatures in the chamber range from a scorching 91 degrees to a comfy 68 degrees to a cool 44 degrees, says Slivka.
As the samples are collected, Slivka and his team are looking at how the tissue responds to stimulation and the way different proteins move within the muscle’s cells. Though the research won’t be done for another 18 months, the findings have been consistent so far: study participants are performing better in cold conditions than hot.
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“Participants feel very comfortable exercising in the environment,” observes Slivka. “Most are a bit chilly for the first five minutes, but the heat produced from exercise quickly warms them.”
Not only that, but the heat didn’t seem to have any positive effect on study participants’ results. “When we have people exercise in a hot environment it really challenged their physiology,” said Slivka in an interview with . “That response appears to be very negative. Almost as if they didn’t work out at all.”
That may be influenced by the way humid conditions can cause the body to overheat, since sweat doesn’t evaporate as readily when the air is already moist. As a result, we don’t sufficiently—and may be less motivated to work hard.
Slivka says his team found that a single bout of exercise in the heat isn’t as effective for mitochondrial development as a single bout of exercise completed at room temperature. But whether that stays true in the long term remains to be seen.
“The current study will let us know if this persists throughout training or if the muscle can acclimate (as the cardiovascular and thermoregulatory systems do) and restore the normal beneficial response to exercise,” he says.
In the meantime, don’t use the new findings to justify blowing off your outdoor run or bike ride. Even if your workouts aren’t as effective in terms of muscle development, exercise is awesome for a ton of other reasons—it relieves stress, gives you an energy boost, and burns calories. Take it indoors where the AC is cranking, and you’ll score all these benefits and more.