The stretch reflex is a protective mechanism that causes the muscle to contract, or shorten, to avoid excessive stretching to the point of injury. When stretching properly, a mild stretch should be felt in the belly of the muscle, not in any of the joints. For example, when stretching the hamstrings or quadriceps, the aim is to feel the stretch in the back or front of the thigh, not in the knee or hip. You should feel as though you could maintain the stretch comfortably for five minutes, even though the recommended time is much less than that. Stretch slowly to the point of tension, never pain.
Flexibility varies greatly from person to person.
This can be counterproductive by activating the stretch reflex or causing injury. Athletes need to relax while they are stretching. Being conscious of one's breathing can be very helpful in learning to relax. Concentrate on breathing more slowly and deeply while stretching. When exhaling, try to stretch the muscle a little further within the limits of pain.