I do yoga every day and some of the poses are held and create shaking, which my yoga teacher always said was a good thing. I recently learned about TRE (Trauma Release Exercises) - there is a good book and video about them. They use stress positions very much like the ones in yoga to release deep stress from the body. So not only are you strengthening yourself when you do this kind of exercise you are releasing old stress or PTSD too. Which is good for your overall health and not just muscle strength!

Here are some links on TRE