1. Pain: If something is painful, muscles tighten to take pressure off the painful structure. This is a protective mechanism.
2. Scar tissue: Scar tissue acts like glue in a muscle. The section of the muscle containing scar tissue will not stretch as much as it should, limiting muscle length.
3. Nerve entrapment: If scar tissue forms next to a nerve, the nerve can become ‘glued’ to the surrounding muscles. Nerves don’t stretch; they should floss in and around muscles. When they stick to muscles, the surrounding muscles will contract to protect the nerve from being stretched.
4. Fatigue: When muscles become fatigued, they tighten.
5. Trigger points: Bands or nodules of irritated muscle fibers that can cause the surrounding muscles to tighten as well.
In each of these cases, stretching would not be an appropriate form of treatment. If stretching were used, improvement would either be delayed or prevented.
Stretching is beneficial in other circumstances. For example, after a nerve entrapment has been released, stretching is used to glide the nerve through the muscles, preventing scar tissue from forming again.