Human movement is dependent on the amount of range of motion (ROM) available in synovial joints. In general, ROM may be limited by 2 anatomical entities: joints and muscles. Joint restraints include joint geometry and congruency as well as the capsuloligamentous structures that surround the joint. Muscle provides both passive and active tension: passive muscle tension is dependent on structural properties of the muscle and surrounding fascia, while dynamic muscle contraction provides active tension (). Structurally, muscle has viscoelastic properties that provide passive tension. Active tension results from the neuroreflexive properties of muscle, specifically peripheral motor neuron innervation (alpha motor neuron) and reflexive activation (gamma motor neuron).
Factors contributing to muscle tension.
Obviously, there are many factors and reasons for reduced joint ROM only one of which is muscular tightness. Muscle “tightness” results from an increase in tension from active or passive mechanisms. Passively, muscles can become shortened through postural adaptation or scarring; actively, muscles can become shorter due to spasm or contraction. Regardless of the cause, tightness limits range of motion and may create a muscle imbalance.
Clinicians must choose the appropriate intervention or technique to improve muscle tension based on the cause of the tightness. Stretching generally focuses on increasing the length of a musculotendinous unit, in essence increasing the distance between a muscle's origin and insertion. In terms of stretching, muscle tension is usually inversely related to length: decreased muscular tension is related to increased muscle length, while increased muscular tension is related to decreased muscle length. Inevitably, stretching of muscle applies tension to other structures such as the joint capsule and fascia, which are made up of different tissue than muscle with different biomechanical properties.
Three muscle stretching techniques are frequently described in the literature: Static, Dynamic, and Pre-Contraction stretches (). The traditional and most common type is static stretching, where a specific position is held with the muscle on tension to a point of a stretching sensation and repeated. This can be performed passively by a partner, or actively by the subject ().
Techniques of Muscle Stretching. HR=Hold relax; CR=Contract relax; CRAC= Contract relax, agonist contract; PIR= Post-isometric relaxation; PFS=Post-facilitation stretching, MET= Medical exercise therapy.
Static stretching of the posterior shoulder (Used with permission of the Hygenic Corporation).
There are 2 types of dynamic stretching: active and ballistic stretching. Active stretching generally involves moving a limb through its full range of motion to the end ranges and repeating several times. Ballistic stretching includes rapid, alternating movements or ‘bouncing’ at end-range of motion; however, because of increased risk for injury, ballistic stretching is no longer recommended.1
Pre-contraction stretching involves a contraction of the muscle being stretched or its antagonist before stretching. The most common type of pre-contraction stretching is proprioceptive neuromuscular facilitation (PNF) stretching. There are several different types of PNF stretching () including “contract relax” (C-R), “hold relax” (H-R), and “contract-relax agonist contract” (CRAC); these are generally performed by having the patient or client contract the muscle being used during the technique at 75 to 100% of maximal contraction, holding for 10 seconds, and then relaxing. Resistance can be provided by a partner or with an elastic band or strap ().
Contract-Relax stretching with stretching strap (Used with permission of the Hygenic Corporation).
Other types of pre-contraction stretching include “post-isometric relaxation” (PIR). This type of technique uses a much smaller amount of muscle contraction (25%) followed by a stretch. Post-facilitation stretch (PFS) is a technique developed by Dr. Vladimir Janda that involves a maximal contraction of the muscle at mid-range () with a rapid movement to maximal length followed by a 15-second static stretch.2
Post-Facilitation Stretching of hamstrings (Used with permission of the Hygenic Corporation).