What exactly Causes muscles to shake?

I don’t know. I am not a professor of physiology.

But I did find one with a great explanation. (And if anyone out there is qualified and would like to contribute, please comment below or email me, and I will update the article.)

Loren G. Martin, professor of physiology at Oklahoma State University in Tulsa, explains what causes muscles to shake with exercise in Scientific American.

He says - drum roll, please - “they’re tired.”

…I am paraphrasing. (Read full article)

But here’s the short of it:

A muscle is controlled by many motor units (a group of skeletal muscle cells and the motor nerve cell to which they connect in the spinal cord).

When a muscle contracts, the motor units all move at different speeds and times, so while one unit within a muscle is contracting, another unit is relaxing. However, because there are so many units working, there is a lot of overlap, which makes the muscle appears to move smoothly. That is, until they get fatigued.

When the motor units get tired (meaning the chemicals that create the electrical impulses becomes depleted and cannot be manufactured and released fast enough to keep up with the level of activity), they drop out.

As more motor units drop out, the muscle has fewer motor units to rely on, which makes the muscle move in a more jerkier motion, hence the shaking.

Chelsea Corley, a Pilates teacher with an M.A. in motor learning theory, explains that the full-body shaking we see in Pilates, the “earthquake shaking,” is more about the brain and body connect of the neural pathway not firing in a correct sequence rather than the muscles being tired.

“All of these motor neurons are firing because the most efficient pathway hasn’t been created yet,” Corley explained. “Your body is experiencing a new way of moving. When your brain learns how to execute these movements more effectively, with practice, the shaking stops and you can focus on actually strengthening the muscle fibers.”

Chelsea has an online school for Pilates teachers, Integrated Teaching Systems, that focuses on motor learning concepts. Check it out here.

Read: Movement Instructor Counting Disorder: Why Pilates Teachers Are So Susceptible, And How They Can Beat The Odds