As a medical massage therapist, Here’s what I know about stretching:
Stretching is a dialogue between muscles and nerves. It’s always seemed downright sweet to me, not to mention, prudent, that the nerves respond to a stretch with a built-in response mechanism called a reflex to keep the muscle from being stretched too far–to the point of injury. Unfortunately, the response often triggers a spasm which is a muscle contraction designed to stopping inhibit the stretch NOW. Quick, jerky movements are highly excitable to the nervous system, triggering the response and cold tissue is more likely to spasm as well.