If you’ve ever noticed your hands swelling midrun or plopped down after the fact to see some swollen fingers, you’re definitely not alone. While it’s often only subtle, it’s actually a pretty common occurrence, so we tapped William O. Roberts, M.D., professor in the Department of Family Medicine and Community Health at the University of Minnesota, to give us the details on this phenomenon.
According to Roberts, your hands usually swell when it’s hot out—but it’s not a sign of dehydration. Rather, it’s the opposite: Hands and fingers swelling can be a sign of hyponatremia, which occurs when you drink too much fluid over the course of a run, he says.
“During exercise, circulation increases, and the hand has a large network of small blood vessels that open up,” he tells Runner’s World. “With the increased blood flow, there is some fluid leak between the cells. This leakage is probably the cause of your fingers swelling.”
Additionally, swinging your arms as you run may also contribute to fluid retention in your hands, since this motion increases air movement across your skin to improve heat exchange with the air.
“This fluid is eventually reabsorbed into the cells or cleared by the lymph system,” he says. “This process is going on while you are running, but the rate of removal is slower than the rate of accumulation. Once you stop exercising, the fluid will reabsorb into the vascular system or surrounding cells or be removed by lymph flow.”
The solution? Roberts says if you notice that your hand swelling is worse when you run in the heat, moving your hard or long workouts to the cooler parts of the day—mornings or night—could help.
Taking off any rings you’re wearing is also not a bad idea—the last thing you want to deal with after a 20-miler is wrestling to get them off of your swollen fingers. (If you really like to keep something like a wedding ring on, you can opt for a rubber version.)
And most importantly, dial in your hydration plan, especially for long runs that last over an hour or have to happen in heat and humidity. One recent study, published in the European Journal of Applied Physiology, suggests that drinking water whenever you want (when you feel thirst) will lead to adequate hydration at the end of a two-hour run despite the temperature. Listen closely to your body to prevent over-hydrating which can lead to symptoms of hyponatremia.
