Stretching and Flexibility Notes

Stretching Activities for Increasing Muscle Flexibility

Objectives

  • Define muscle flexibility and identify its benefits.
  • Identify autogenic and reciprocal inhibition, including the neurophysiologic properties of each.
  • Apply autogenic and reciprocal inhibition properly, both together and separately, in proprioceptive neuromuscular facilitation (PNF) within the established plan of care.
  • Identify and apply appropriate clinical guidelines and indications for static, ballistic, and PNF stretching within the established plan of care.
  • Apply common static stretching activities for the muscles of the upper and lower extremities and cervical and lumbar spine within the established plan of care.

Muscle Flexibility

  • Definition: The ability of a muscle to lengthen, allowing one or more joints to move through a range of motion (ROM).
  • Loss of flexibility: A decrease in the muscle's ability to deform, resulting in decreased ROM about a joint.

Benefits of Enhanced Flexibility

  • Reduced risk of injury
  • Pain relief
  • Improved athletic performance
  • Goal: Improve ROM at a given joint by altering the extensibility of the muscles that produce movement at that joint.

Neurophysiologic Properties of Muscle

Sensory Organs
  1. Muscle spindle
  2. Golgi tendon organ (GTO)
Neurophysiologic Phenomena
  1. Autogenic inhibition
  2. Reciprocal inhibition
Muscle Spindle
  • Specialized receptor within muscles consisting of unique muscle fibers, sensory endings, and motor endings.
  • Contains intrafusal muscle fibers, distinct from ordinary skeletal muscle fibers (extrafusal fibers).
  • Sensory endings respond to changes in muscle length and the velocity of these changes.
  • Intrafusal fibers connect to extrafusal fibers, so stretching the muscle stretches the intrafusal fibers.
  • Afferent sensory nerves arise from intrafusal fibers:
    • Type Ia afferent sensory nerves: respond to quick and tonic stretch of the muscle.
    • Type II nerves: monitor tonic stretch.
  • Activation: When the muscle is stretched, type Ia and II afferent sensory nerves of the intrafusal fibers are activated.
  • Muscle Spindle Reflex: Activation causes the stretched muscle to contract, resisting the stretch.
    • Example: A clinician applies a quick stretch to the hamstring muscles. The intrafusal muscle fibers react by sending impulses to the spinal cord, informing the central nervous system (CNS) that the hamstring muscles are being stretched. Nerve impulses return from the CNS to the extrafusal muscle fibers via motor neurons to contract the hamstring muscles reflexively, resisting elongation.
Muscle Fiber Types
  • Type I (slow-twitch) fibers:
    • Slower twitch speeds.
    • Relatively fatigue resistant.
  • Type IIa (fast-twitch oxidative glycolytic (FOG)) fibers:
    • Higher twitch speeds than type I fibers.
    • Less fatigue resistant.
Golgi Tendon Organ (GTO)
  • Encapsulated structures attached in series to the fibers of the tendons at the junction of extrafusal muscle fibers and tendons.
  • Sensory nerve afferent fibers (type Ib) are attached to small bundles of the tendon within the capsule.
  • Sensitive to slight changes in the tendon’s muscle and responds to added tension by both passive stretch of a muscle (especially at the lengthened range) and active muscle contraction.
  • Role: Prevent overactivity of the nerve fibers innervating the extrafusal muscle.
  • Mechanism: If a muscle is stretched for a prolonged period or if an isometric contraction occurs, the GTO fires and inhibits tension in that same muscle, allowing it to elongate.
    • Example: Hamstring muscles stretched for 15 to 30 seconds create tension in the tendon. The GTO responds via type Ib nerve fibers, overriding impulses from the muscle spindle and allowing the hamstring muscles to relax reflexively.

Major Proprioceptive Receptors

  • Muscle spindle
  • Golgi tendon organ

Autogenic Inhibition

  • Definition: Stimulation of a muscle that causes its neurologic relaxation.
  • Mechanism: Occurs when the GTO is activated.
    • Example: A maximal isometric contraction of the hamstring muscles increases tension in the GTO. Impulses from the GTO protect the hamstring muscles by inhibiting motor neuron activity, causing the muscles to relax.
  • Significance: Serves as the basis for PNF stretching techniques.

Reciprocal Inhibition

  • Definition: Interaction within the spinal cord where the contraction of one muscle group results in the relaxation of the opposing muscle group.
  • Demonstration: Flex the elbow and stiffen it. Place the other hand around the upper arm to feel the biceps and triceps muscles harden (contracted state). When a friend pushes upward against the hand, the biceps briefly “softens” (becomes inactive).

Stretching Exercises

  • Static stretching
  • Ballistic stretching
  • Dynamic stretching
  • Active stretching
  • Passive (or relaxed) stretching
  • Isometric stretching
  • PNF stretching
Static Stretching
  • Definition: Gently stretching the muscle to feel a gentle pull, holding the stretch for upwards of 10 seconds, then relaxing.
  • Method: Slowly elongate the muscle to tolerance (a comfortable stretch, short of pain) and hold the position with the muscle in this greatest tolerated length.
  • Neurologic Effects:
    • Slow, prolonged stretch reduces the reflex contraction from the muscle spindle.
    • Holding the static stretch long enough may minimize the effect of the type Ia and II afferent fibers from the muscle spindle.
    • The lengthened position places tension on the tendon, facilitating the GTO to protect the muscle being stretched. This facilitation of the GTO fires type Ib nerve fibers, which inhibit and relax the muscle being stretched (autogenic inhibition).
    • Combined neurologic effects: Minimizing the influence of the muscle spindle and facilitating the effect of the GTO.
Ballistic Stretching
  • Definition: Imposing repetitive bouncing or jerking movements on the muscles to be stretched (e.g., sitting toe touch).
  • Concerns:
    • The quick, jerking ballistic motion can exceed the limits of muscle extensibility in an uncontrolled manner, resulting in injury.
    • Quick bouncing stretches the muscle spindle, activating it and sending sensory impulses to the spinal cord via type Ia afferent nerves, informing the CNS that the muscle is being stretched. Impulses returning to the muscle via motor neurons cause the muscle to contract, resisting the stretch.
    • Facilitation of the muscle spindle may cause microtrauma in the muscle due to the tension created when the muscle is stretched.
  • Clinical opinion: Ballistic stretching has generally fallen out of favor among most clinicians because of the possibility of injury caused by uncontrolled jerking and bouncing motions and because the activation of the afferent nerve fibers of the muscle spindle causes a contraction of the same muscle that is being stretched.
Proprioceptive Neuromuscular Facilitation (PNF)
  • Definition: Methods of “promoting or hastening the response of a neuromuscular mechanism through stimulation of the proprioceptor.”
  • Applications: Used to strengthen and increase flexibility of muscle.
  • Terminology: Varied widely, including contract–relax, hold–relax, slow reversal hold–relax, agonist contraction, contract–relax with agonist contraction, and hold–relax with agonist contraction.
Dynamic Stretching

Involves stretching your muscles whilst moving, either by leg swings or by performing sports-specific drills.

  • Popular for warming up.
PNF Stretching Techniques
  • Hold-relax
  • Contract-relax
  • Rhythmic initiation
  • Passive or Active-assisted
Muscle Energy Techniques (METs)

  • Similar to PNF, developed around the same time in Osteopathy.

  • Uses an isometric contraction of the agonist prior to stretching.

  • Difference: The force of the isometric contraction is a lot lower in METs.
    Using the hamstrings as an example: A MET stretch is performed in the following way

  • History: Developed by Dr. Herman Kabat in the 1940s for treating neuromuscular diseases, including polio and multiple sclerosis.

  • Effectiveness: Research suggests PNF stretching may be the most effective stretching technique for increasing range of motion.

  • Technique: Stretching the muscle to its limit triggers the inverse myotatic reflex, a protective reflex that relaxes the muscle to prevent injury.

Types of PNF Techniques

  1. Autogenic inhibition
  2. Reciprocal inhibition
  3. Combined