Sometimes during certain exercises, my muscles quiver involuntarily, especially when I'm doing ab work. Does this happen to you?
Good news: That shaking means you're working and strengthening your muscles. But it's also a sign that the muscle is not accustomed to the demands you're putting on it.
The trembling indicates how the muscles grab and release one other as they lengthen and shorten during the exercise. But that action will become smoother, and the shaking will stop, once the muscles become more used to the activities you're doing.
Although the shaking isn't dangerous, the fact that you're putting extra demand on the muscles could result in some soreness the next day. The soreness reflects the fact that there's some muscle damage, but when the body repairs it, you come back fitter and stronger in the end, so it's a good thing.
Just think - If you do the exercise everyday then you will get stronger and shake less. Test that theory by doing the 4 minute short, sweet and complete ab routine everyday.
Fit's Tips: So don't overexert yourself too much. If you find yourself quivering from the start, take the intensity down a bit, and ease your muscles into working harder gradually.