Well+Good explains why muscles shake during a workout and if its a good or bad sign in an interview with experts including Matthew Accetta, MS, ACSM-CEP, CSCS*D, CSPS, exercise physiologist at HSS. 

Muscle shaking during exercise can have two possible causes, according to  Accetta. First, your muscles might be tired. Or they might be trying to do something they’re not used to, like a new movement or lifting a heavier weight. In both cases, shaking is a sign that your nervous system is trying to recruit more muscle fibers to get the job done.

“As muscle fibers become fatigued during exercise, your body needs to stimulate more muscle fibers, which require more motor neurons to fire,” Accetta said. “The impulses that travel through the nervous system and to the neuromuscular junctions to carry out activity are what cause the muscles to twitch and shake.”

If you’re trying out a new move, you might expect shaking. “When the body experiences a new stimulus, it might require new muscle fibers and neuromuscular junctions to activate,” Accetta said. “As those fibers and junctions activate for the first couple of times, they might twitch and shake until they become accustomed to the stimulus.”

Shaking is not something that you should ignore, but it doesn’t necessarily mean you need to totally quit your workout, either. The best way to understand this signal is to think of shaking like a “yellow light,” according to Accetta.

“Muscle shaking during exercise should be viewed as a sign to slow down and be ready to take a break, kind of like a yellow traffic light,” Accetta explained.

Read the full article at wellandgood.com.