Are your pecs flickering like a strobe light on the bench?
Those tiny, uncontrollable spasms are called muscle fasciculations, says Dr Christopher Minson, a professor of human physiology at the University of Oregon.
Might sound scary – but in most cases you've got nothing to worry about. These spasms are often caused by an imbalance of electrolytes in your muscle fibres as they fatigue.
To eliminate the spasms, 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 45 minutes, go with a sports drink.
These drinks 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 Dr Michael Ryan, 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.