Why Your Muscles Shake During Your Workout — Especially Barre & Pilates

mbg Associate Movement & Wellness Editor By Ray Bass, NASM-CPT
mbg Associate Movement & Wellness Editor

Ray Bass is the associate movement and wellness editor at mindbodygreen and a NASM-Certified Personal Trainer. She holds a degree in creative writing from the University of Pennsylvania, with honors in nonfiction.

Shaky Muscles During A Workout? Here's Why That's A Good Thing

Image by Lumina / Stocksy

"Up an inch, down an inch. Lift and lower."

Those were the words of another barre instructor at yet another barre class—I think I've taken 300 at this point. She continued shouting words of encouragement while I tried for the 301st time to get into the desired position without looking like a plate of Jell-O.

Truth be told, no matter how often I take barre or Pilates, my muscles shake during class. I know that's what most instructors encourage and look for, but I've never understood what it meant or why it happens. Have I never used those muscles before? Does shaking mean I'm getting stronger?

Here's the lowdown on why your legs shake during barre (and any other workout).

Why do our muscles shake during a workout?

According to Lauren Kanski, an NYC-based NASM-certified personal trainer, the reason our muscles shake during a workout is similar to why they shake after a workout—it's usually from low blood glucose or muscle fatigue. In other words, shaking indicates that we're either low on glycogen or our muscles are tired.

"This is the same concept as the blood and muscle glucose availability," Kanski told mbg. "Working out fed versus fasted can make a huge difference in glycogen depletion. With regards to muscle fatigue, some muscle fibers fatigue faster than others, which cause irregular contractions, or shaking."


Why do our muscles seem to shake more in barre or Pilates classes?

As it turns out, getting the "shakes" in a barre or Pilates class isn't because those muscles haven't been used before—it's because we're isolating different muscles and exhaust them more quickly than we do in other forms of exercise.

Or, as Kanski puts it, "We stretch and lengthen our muscles for longer periods of time in barre and Pilates—this causes quick muscle fatigue and burnout."

OK, so what does it mean?

Is shaking during a workout a good thing? The short answer is yes. Kanski notes that the idea behind strength training is that we damage our tissue so the body can regenerate new, stronger, more durable tissue. That’s why we get sore, after all.

"Shaking is normal and is an indicator of successful progressive overload protocol," she says. "It's the key to making us stronger!"

Bottom line: If you're trying to get stronger, it's time to embrace the shake.

And if you're more of a "muscles shaking after your workout" person—don't worry, we have answers for you, too.

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