Hitting the weights can tire your muscles out, but it also could spur a little action from them, too.

Your muscles can actually start twitching involuntarily when you’re lifting. What gives?

Those tiny, uncontrollable spasms are called muscle fasciculations, says Christopher Minson, Ph.D., a professor of human physiology at the University of Oregon.

It sounds scary, but in most cases, they’re nothing to worry about. These spasms are often caused by an imbalance of electrolytes in your muscle fibers as they fatigue.

Your move, then, is to make sure you stay hydrated before and during a workout. This helps maintain the equilibrium of electrolytes in your muscle cells, explains Minson.

Cold water is best for most workouts, but if you’re working out for longer than 30 minutes, grab a sports drink.

These beverages offer potassium, sodium, and other electrolytes to replenish what your body lost through sweat.

If the twitch continues for days or disrupts your sleep, you should see a doctor. In rare cases, severe pain or a sustained twitch could be a sign of a tear or strain, says Michael J. Ryan, Ph.D., associate professor of exercise science at Fairmont State University.

What’s more, spasms that last a long time or occur on a regular basis may be a sign of kidney or thyroid dysfunction, fibromyalgia, or other neuromuscular disorders.