why do muscles shake?

After a particularly energetic yoga class, some of my tuckered fellow-yogis expressed their challenges with asanas like Full Boat Pose and Chatarunga Push-ups. "Why do my muscles shake so bad!?" a student laughed. We've all been there (especially in Full Boat) when the uncontrollable shaking of our fatigued muscles becomes a distraction or requires us to back out of a pose.  I knew that shaking muscles basically indicate muscle weakness or fatigue, but I was curious about the science behind it myself. What I found out about our shaking muscles is very interesting and enlightening!

What's actually happening when my muscles quiver?
When your muscles begin to quiver in a challenging posture, it's because different parts of the muscle are grabbing and releasing one another as they lengthen and shorten. Once your muscles become accustomed to doing that exercise, the trembling will stop.

"Muscles are made up of many fibers. When a muscle is used, not all the fibers contract at the same time. Some rest while the others work, and then they trade places. When the muscles are really challenged, the changeovers can get a little ragged. Beginning yogis often shake quite a lot."- Yoga Journal

So it's really the link between muscle fibers that are struggling and causing the shuddering. A good analogy for this connection would be runners passing the baton in a relay race; when you're quivering, someone fumbled the baton.

Are shaking muscles bad?
The answer to this is on an individual basis. In yoga, we always emphasize the importance of tuning in with what your body and mind are feeling. It's okay to be challenged or find that "comfortable edge" in a posture, but if you're forcing yourself to hold a posture that's too much for you, stop and analyze your intentions. Yoga asanas are only meant to gradually challenge a focused and prepared mind and body. Check your mind, your eyes, your lips/jaw, and, most of all, your breath. If any of these areas feel hard or constricted, back off and modify the pose to fit your needs for the day.

If muscles continue to shake AFTER asana practice, that's when you know you've pushed too hard (and you might want to confront the dreaded ego.)

"When the muscles continue to shake uncontrollably, it is a strong indicator that the practice has been far too violent."- Yoga Journal

How can I stop the shaking?
Short of backing out or modifying the posture that is causing the shaking, the best way to avoid shaking in the future is to stick to a regular practice. When you're in the posture that you struggle with, imagine that you are rooting your muscles to the bone, creating a strong base. Start slow and keep surrounding areas relaxed. Practicing and slowly strengthening the muscles will allow you to eventually move past the shaking.

Summary:
Your muscles shake when they're struggling to accommodate a new challenge. Shaking is okay as long as your stay mindful and it doesn't become a mental distraction. You may be sore the next day, but it should feel good as long as you don't overdo it. If you always stay tuned-in, you'll always stay safe!