Janet Rosen wrote:
individual muscle fibers within a muscle can be contracted or relaxed and that will affect overall muscle length. dancers w/ tight quads have shortened quads that pull the pelvis bones in such a way that their butt's stick out. i have opposite: chronically tight hamstrings -- a tendency that conventional stretching does not affect-- that pull the pelvis in the opposite direction and flatten my lumbat curve abnormally, giving rise to low back discomfort.
so, no, bones won't grow or break, but bone position within the body can and does change due to the force of muscles, tendons, etc.
So if I understand what you are saying, someone moving their wrist towards their head, causing their elbow to bend, will contract the bicept. And yes, that will make the bicep "peak" and appear shorter. They can drop their wrist to their waist which will contract the tricept, and allow the bicept to relax. If that's "lengthening" the bicep, then yes, all muscles do that by nature of their ability to contract.
What I'm saying is that the true length of the muscle, determined by it's connections to the skeletal system cannot be lengthened by any activity unless bone is broken. Exercise, stretching, whatever....cannot accomplish that. Further, the shape of the muscle is determined by genetics, and no excercise routine or stretching, or whatever is going to change that either. So, speaking of "lengthening" the muscle or "changing the shape of a muscle" in reference to an exercise program, stretching routine or late-night infomercial is misleading.