True and false. While sweat rate can be slightly lower when you’re exercising in cooler weather, you’re still sweating a good amount—especially if you’re wearing heavier clothing to stay warm. Cooler weather has been shown to decrease thirst, so staying hydrated may require more conscious effort; consider whether room-temperature fluids are more palatable in the cold.
The best way to determine your sweat rate in cold weather is to measure your weight before and after your run, along with the amount of fluid you drink during the run. Starting with the total fluid consumed while running, add in 16 to 24 ounces of water for every pound of weight lost. That’s how much fluid you need to consume to maintain full hydration.
But you may not need to stay fully hydrated in the cold. Research has shown that mild dehydration (about 2–3 percent of body weight) in cold weather is not always detrimental to performance—particularly in submaximal training (i.e. an easy jog). However, research has yet to definitively determine whether mild dehydration has an impact on performance during more intense workouts in the cold. Depending on how long and how hard you’re running, carbohydrate and electrolyte replacement may be needed as well.
Take-Home: You still need to hydrate while running in the cold; find a fluid and a beverage temperature that are most palatable for you. However, you may not need to pound the fluids as much as in warmer weather. To be safe, measure how much weight you lose from a run and make sure your fluid intake maintains a weight loss of no more than 2 percent of your body weight—no more than a three-pound weight loss for a 150-pound runner. You may want to make a more conscious effort to hydrate when running longer, harder, or in heavy clothing.
Jason Machowsky, MS, RD, CSCS, is a registered dietitian, certified strength and conditioning specialist, and certified personal trainer at the Tisch Performance Center at Hospital for Special Surgery. He has an undergraduate degree from Cornell University and a Masters from Columbia.