If you’ve ever experienced “barre shake” while plié-ing or trembled during a plank, you might have wondered what makes your muscles occasionally feel shaky when you’re working out.
It’s actually pretty common to shake during a workout, and there are several reasons why it might happen. Fatigue is often one of them, but the more contributing factors there are, the stronger the quivering becomes.
Here are five reasons you may shake during a tough workout — and what you can do about it.
This is the most common culprit. When you work out, your brain sends electrical signals to your muscles that regulate the rate and strength of their contraction. “When your muscles begin to fatigue, you start to lose some of that neural coordination, and [when that] happens, smaller stabilizer muscles kick in,” explains Shawn Arent, PhD, CSCS*D, FISSN, FACSM, director of the Rutgers Center for Health and Human Performance.
When you’re pushing yourself past your limits, that process can become a bit irregular, which can cause shaking. This is especially noticeable when you’re fighting to hold your position during isometric exercises like planks.
And it’s not just your muscles that can get fatigued — if you haven’t slept well, it can affect your workout in many ways, and that includes feeling shakier.
This is more likely to happen toward the end of a workout, Arent says. Our muscles need the right amount of electrolytes in order to contract, so dehydration can impact your performance and potentially cause you to shake.
Your muscles store carbohydrates as glycogen to use as fuel. If you’re low on glycogen — either because it’s been awhile since you last ate or because you’re eating inadequate carbs — your body may let you know by shaking.
Switching up your workouts so that you use muscles in new or different ways can help you grow stronger, but there’s a period of adaptation that goes along with that. Shaking is common during that period. “As you get better at optimally contracting the muscles involved [in the exercises you’re doing], that shakiness goes away,” Arent says.
“Shaking is often a physiological response to intense, fatiguing work — so if it occurs, it’s probably the result of you pushing yourself too hard, most likely with new, different, or particularly grueling workouts,” says Trevor Thieme, CSCS, Openfit’s senior manager of fitness and nutrition content. HIIT, MetCon, and heavy leg days are all notorious for causing shaking.
How to Prevent Muscle Shaking
There are a few simple strategies that can help you avoid — or at least minimize — shaky muscles during a workout. First, make sure that you’re getting enough sleep at night, and fuel and hydrate properly before you work out. Also, pace your workouts so that you progress at a manageable pace. “If you’re starting to shake during workouts with greater frequency, it can be a sign that you’re overreaching or overtraining, so dial back your training intensity,” Thieme says.
As you get stronger, the shakiness should subside a bit: “The better your muscular endurance gets, the better able you are to stave it off,” Arent says.
If you feel shaky even when you’re not fatigued, however, it may be sign of hypoglycemia or something else. “Shaking should be a temporary response,” Thieme says. “If you’re still shaking long after your workout ends, give your doctor a call.”