There are certain physical things you expect to happen with exercise, like getting breathless, sweaty, or fatigued. But when something out of the ordinary occurs—numb hands after a workout or tingly fingers and toes during your cardio session, for instance—it’s only natural to feel a little unnerved.

Maybe your foot feels like pins and needles halfway through your elliptical session. Or your hand loses sensation while you’re busting out a set of overhead presses. Perhaps you step off the stationary bike only to be greeted by a numbness in your toes. Whatever the scenario, it’s understandable to feel caught off guard by it. After all, why would your extremities feel like they’re falling asleep when, in fact, they are very much awake and working hard?

Though it may feel disconcerting when it happens, foot and hand tingling and numbness during workouts is actually more common than you might think—affecting exercisers in a variety of routines—and in many cases, it’s really nothing to worry about. As for numbness or tingling that persists or crops up after your exercise session wraps, well, that could be a sign of something more concerning, depending on what other symptoms (if any) you are experiencing.

To get a better grasp on that exercise-related pins and needles sensation, SELF chatted with experts to learn what triggers them, how to alleviate them, and when you should check in with a doctor. Here’s what you need to know.

What causes numb hands when exercising?

Tingling or numbness in the hands is usually a sign that blood flow to the nerves is being blocked—it’s generally not due to simply overworking your muscles, Alice Chen, MD, a physiatrist at the Hospital for Special Surgery in New York City, tells SELF.

The countless nerves that run throughout our bodies are super sensitive, sensory nerves—the ones that give feeling—even more so. Even a slight change in blood supply to those nerves can affect what we feel, resulting in numbness and tingling (there’s an actual term for that feeling, by the way; it’s called paresthesia). “The most common cause for changes in blood supply to nerves in a healthy person is positional,” Jeffrey M. Gross, MD, medical director at NYU Langone Physical Medicine and Rehabilitation Associates, tells SELF. It’s the same reason your arm may get numb if you fall asleep on it—that position blocks blood supply to the nerves.

Positioning issues are especially common during cardio. When you’re running, using the elliptical, or even vigorously walking, your arm is often bent at the elbow. Quick anatomy refresher: Your ulnar nerve—your “funny bone,” which yes, is actually a nerve—runs along the inside of your forearm and down to your pinky and ring fingers. When your elbow is bent, this position forces that nerve to stretch across the bone in your elbow. This cuts off its blood supply, which in turn makes your pinky and ring fingers feel tingly and numb. “Everyone’s anatomy is a little bit different, so some people are more prone to this than others,” Dr. Gross says.