Flexibility

Stretching: an activity wherein a person purposefully attempts to increase ROM by applying a longitudinal force to a muscle

Elastic effects: increase in tissue length that immediately returns to the original length when stress is removed

Viscous effects: increase in tissue length that is dependent on time and returns to the original length at a slow rate (i.e., it is reversible); viscous effects occur because molecules move when force is applied over time, and thus, the return to original length is not immediate

Viscoelastic effects: a combination of viscous and elastic effects

Plastic effects: a permanent change in the molecular structure of a tissue, as that which occurs when force is applied to a plastic sheet without completely tearing it. Plastic deformation indicates that damage has occurred to a tissue—it does not occur with appropriate stretching (i.e., the ROM returns to normal within a reasonable time frame after appropriate stretching)

Flexibility training: program of stretching exercises designed to increase ROM of targeted joints to a desired level or to maintain that level once it is attained

The immediate gain in ROM with stretching is mostly limited to the muscle being stretched, with some increase in the contralateral limb as well. This suggests that a neurologic reflex is one of the mechanisms for the effects of an acute stretch.

If one stops moving a joint, one loses flexibility. It is unknown how much or how often movement is necessary to maintain flexibility.

Most studies have suggested that the effectiveness of stretching increases when the tissue is warmer.

The most effective way to increase muscle temperature is with muscle activity, although deep heating methods (e.g., ultrasound) can be effective.

Superficial heat is not an effective method to warm deep muscles.