It’s entirely possible that you could stretch so much that you strain, or even tear, a muscle, but more likely than not, that pinch is probably just a startled nerve. Muscles contain special sensory receptor cells called muscle spindles. When you stretch, these cells send a signal to the neurons within the muscle to tell the central nervous system that you’ve gone too far. As a result, those muscles contract, tighten, and resist the pull. That reaction is what causes the initial painful feeling that people get when they attempt to stretch. It’s also the reason that some people feel such agony when they try to touch their toes: The quick pain caused by that neural cascade is just too great.