It's less than comforting to see your muscles shaking when you're hoisting dumbbells over your head or to feel your abdominal muscles quiver as you try to set a personal best record for the plank. What gives?
A couple different reasons may be behind the shakes. Most often it's due to a build-up of lactic acid in the muscle from overuse, says Beyer. "If you're doing something isometrically, meaning you hold a position for an extended period of time, like a "wall sit" in a squat position against a wall or a plank, the muscles get overtired and poop out over a period of time." It's normal and should go away when you stop the exercise. It doesn’t mean you’ve hurt anything, but use common sense, says Beyer. "If it hurts you or you're in pain afterward, dial it back. Try fewer reps and remember to work up [to more reps] gradually."