A new study found that when trained runners wore extra clothing while exercising in 60-degree weather, their sweat rate and body temperature increased. The findings suggest that layering up can help you acclimate to heat, even in low temps.
In colder weather, you release heat through sweat and increased blood flow near the skin, says study author Brett Ely, a Ph.D. candidate in human physiology at the University of Oregon in Eugene.
But on a hot day when your body is as warm as the outside air, you rely almost entirely on sweat to cool down. That means you get dehydrated more quickly, which increases your heart rate and perceived effort. Luckily, your body acclimates to the heat after just five to 10 hour-long workouts in high temps, which makes the heat less taxing on your system.
Overdressing can have the same effect: “The extra insulation traps heat close to your skin and waterproof layers trap moisture from your sweat,” Ely says. This creates a hot, humid microenvironment that makes your core temperature rise, mimicking hot weather.
To prep for a summer race or get used to the heat before it gets too sweltering, wear extra layers on your runs, like a long-sleeved top and windbreaker instead of just a tee. Ely suggests you start with one layer to ease your system into the heat. Add layers over the next eight to 10 runs. You should feel very warm and sweaty, but not unbearably hot, she says. Pay attention to cues like lightheadedness, cramping, and excessive fatigue—these are signs of heat injury and mean you should ditch a layer.