Muscle fibers work all day, every day shortening and lengthening to make the body move. But not everyone can be a smooth operator— at least not all the time. When those muscles start shaking mid-exercise, research suggests a few things could be to blame, ranging from fatigue to dehydration  .
Shake, Rattle, and Roll — The Need-to-Know
Photo by Marissa Angell
In one study, researchers traced unsteady muscles to exhaustion or fatigue, particularly from more intense exercise (like sprinting or resistance training), which relies on fast muscle contraction  . But why the shake-up? These muscles are actually smarter than they look, divvying up the workload between fibers (some work while others rest, and then “switch!”) . But as they're challenged more and more, this job-swapping can get a little ragged, causing muscles to lose their steady motion . The shaking? Just the body’s signal that it might be quittin’ time .
Muscle endurance can also be a factor. If those hammies haven’t completely recuperated from yesterday’s killer workout, the muscles are forced to work harder than usual to keep up. Trying a new exercise can also cause fatigue to hit faster, making the muscle shake its groove thing— and not in a good way  .
And then there’s dehydration. When the body gets low on fluids (which can also cause electrolytes to get off kilter) the connective tissue has trouble doing its job— including transmitting signals from the brain down to the muscle fibers. And with a garbled message about when to contract, the firing sequence can get noticeably out of whack . Hence, the Harlem Shake.
All Shook Up — Your Action Plan
For some, shaking muscles can be like a badge of honor marking an intense workout. Still, there’s no solid evidence suggesting this is something exercisers should try to work through. Since shakiness can be especially common toward the end of an exercise, the muscle may be close to exhaustion, signaling it might just be time to call it a day . A solid warm up and stretch session might also keep shaking at bay by helping to reduce muscle fatigue from the get-go .
But if the muscle starts to shake toward the beginning of the exercise, it may be more of a warning sign that the exercise is too difficult for the body to handle, so scaling back on the intensity or lightening up on the weights may be necessary.
Generally, as muscles get stronger and become accustomed to an exercise, shaking will happen less, but everyone responds differently to exertion. So it’s possible for some to reduce the effects of shaking by improving muscle endurance, while others may experience shaking muscles with every workout, regardless of how experienced they are in the weight room  .
No matter how hard the exercise routine, be sure to maintain good nutrition and hydration to help counteract shaking due to factors like dehydration and electrolyte balance. Getting enough fluids throughout the workout will help keep the tissues happy and hydrated, so the signal from the brain to the muscle fibers won’t get lost in translation.