General Principles

  • The term flexibility is often used as a synonym for range of motion (ROM) around a joint.

  • Both muscles and ligaments can limit ROM.

  • Mobility refers to a limited ROM because of ligaments; flexibility is usually reserved to refer to limited ROM caused by the muscle–tendon unit.

  • Flexibility depends on both muscle stiffness (force required to stretch a muscle) and the stretch tolerance of an individual (amount of discomfort felt when a muscle is stretched).

Definitions of Related Terms

  • 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

Specificity of Flexibility Training

  • 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.

Effects of Temperature on Flexibility Training

  • 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.

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