Have you ever noticed that on hot and humid days, your workout suffers? If you're a runner, you may have noticed that on balmy days, you can't quite get the speed or time you're used to getting.
I read an article recently that explains why and interestingly enough, it has nothing to do with how much water you drink or pour over your head.
The effects of heat and humidity on athletic performance
One reason performance declines on sultry, humid days is that working muscles have to compete with the skin for blood. Directing more blood to the skin removes body heat and helps keep your body’s temperature from rising to dangerous levels. But that can mean less blood reaches muscles. At the same time, when your body becomes hotter, muscle enzymes speed up, burning glycogen more rapidly, depleting stores of the sugar that the muscles use for fuel.
Scott Montain and Matthew R. Ely, researchers at the United States Army Research Institute of Environmental Medicine in Natick, Mass., analyzed real-world data from seven major marathons, comparing performances over years when temperatures and humidity varied but the race course remained the same. Heat affected slower runners more, probably because they were on the course longer and ran in packs. Warm bodies close together make it harder for one’s body heat to dissipate.
Which is best for exercise - morning or evening?
Dr. Cheuvront said that if you have to choose between exercising in the morning when it is 60 degrees and 80 percent humidity, or in the evening when it is 90 degrees and 50 percent humidity, choose the morning.
Acclimating to the heat
Yet as challenging as heat and humidity are, people can acclimate. Blood volume expands, which reduces the strain on the heart from the increased demand for blood flow to the skin and muscles. And sweating increases — people who are heat adapted sweat sooner and more profusely, allowing their bodies to cool more efficiently.
For example, if you are not acclimated and run for an hour in 98-degree heat, your core temperature may go up to 103 degrees, bordering on the danger zone, said Craig Crandall, who studies heat acclimation at the University of Texas Southwestern Medical Center in Dallas. But if you are acclimated, your temperature might be 101 degrees after an hourlong run, which is well within the safety zone. Acclimation takes at least five days, Dr. Cheuvront found. He first asked participants to walk on a treadmill for 100 minutes in a room that was kept at 100 to 120 degrees.
On Day 1, Dr. Cheuvront said, they usually last 30 to 45 minutes. Then, he added, they will either request to get off the treadmill; collapse; or reach the safety-limit core temperature of 104 degrees, at which point they are stopped. By Day 5, just about everyone lasts 100 minutes.
It is possible to adapt even more. Dr. Cheuvront’s subjects continued to improve when they walked on the treadmill in that hot room for five more days.
Some people naturally adapt to heat much more than others. But Dr. Cheuvront said he had never come across a person who did not adapt at all.
The key to acclimation, he said, is to exercise in the heat daily and to be sure you are sweating profusely — wearing extra layers of clothing can help if you are exercising indoors or in cooler weather. Given a choice between spending more time in the heat but exercising less intensely, or less time and exercising more intensely, it is safer to choose to go longer and work less intensely, he said.
Read the entire article here.
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