PNF Stretching –The Role of the Stretch Reflex The muscle spindle is a long thin nerve receptor found within the muscle. Information from this receptor transmits information to the spinal cord regarding muscle length and the speed of lengthening. When a muscle is stretched quickly this muscle spindle fires and causes a reflexive contraction within that muscle that is undergoing the stretch. The greater the speed of stretch, the stronger the reflex contraction in the muscle being stretched.
PNF Stretching – Reciprocal Inhibition
inhibition of the antagonist muscle group is mediated by the muscle spindle. If the agonist muscle contracts, then the spindle fires, sending messages to the spinal cord causing the antagonist muscle to relax. PNF StretchingAutogenic Inhibition – The Golgi tendon organ is a nerve receptor found in tendons. This receptor fires when tension increases within the tendon. This tension can be due to stretch or contracting muscle. When the Golgi tendon organ fires a signal is sent to the spinal cord causing the agonist muscle to relax. During pnf stretching, these three mechanisms all work together to allow normal smooth movements and can be manipulated through PNF techniques to increase our ability to stretch.
Basic PNF Techniques
Two techniques are seen in the literature more frequently than others, the contract-relax method (CR) and the contract-relax-antagonist-contract method (CRAC) of PNF. The CR method included the target muscle (TM) being lengthened and held in that position while the participant contracted the TM to its maximum isometrically for an allotted amount of time.
- Reversal of Antagonists – A group of techniques that allow for agonist contraction followed by antagonist contraction without pause or relaxation.
- Dynamic Reversals (Slow Reversals) – Utilizes isotonic contractions of first agonists, then antagonists performed against resistance. Contraction of the stronger pattern is selected first with progression to the weaker pattern. The limb is moved through a full range of motion.
- Stabilizing Reversals – Utilizes alternating isotonic contractions of first agonists, then antagonists against resistance, allowing only a very limited range of motion.
- Rhythmic Stabilization (RS) – Utilizes alternating isometric contractions of first agonists, then antagonists against resistance; no motion is allowed.
- Repeated Contractions, RC (Repeated stretch) – Repeated isotonic contractions from the lengthened range, induced by quick stretches and enhanced by resistance; performed through the range or part of the range at a point of weakness. The technique is repeated (i.e., three or four stretches) during one pattern or until contraction weakens.
- Combination of Isotonics (Agonist Reversals, AR) – Resisted concentrically, contraction of agonist’s muscles moving through the range is followed by a stabilizing contraction (holding in the position) and then eccentric, lengthening contraction, moving to slow back to the start position; there is no relaxation between the types of contractions. Typically used in antigravity activities/assumption of postures (i.e., bridging, sit to stand transitions).
- Rhythmic Initiation (RI) – Voluntary relaxation followed by passive movements progressing to active assisted and actively resisted movements to finally active movements. Verbal commands are used to set the speed and rhythm of the movements. Light tracking is used during the resistive phase to facilitate movement.
- Contract-Relax (CR) – It is one of PNF Techniques usually performed at a point of limited ROM in the agonist pattern. Strong, small range isotonic contraction of the restricting muscles (antagonists) with emphasis on the rotators is followed by an isometric hold. The contraction is held for 5-8 seconds and is then followed by voluntary relaxation and movement into the new range of the agonist pattern. Movement can be passive but active contraction is preferred.
- Contract-relax-active-contraction (CRAC) – Active contraction into the newly gained range serves to maintain the inhibitory effects through reciprocal inhibition.
- Hold-Relax (HR) – It is one of PNF Techniques usually performed at a position of comfort and below a level that causes pain. Strong isometric contraction of the restricting muscles (antagonists) is resisted, followed by voluntary relaxation, and passive movement into the newly gained range of the agonist pattern.
- Hold-relax-active-contraction (HRAC): Similar to HR except for movement into the newly gained range of the agonist pattern is active, not passive. Active contraction serves to maintain the inhibitory effects through reciprocal inhibitions.
One PNF technique that Black says can trigger the reflex is commonly called “hold-relax.” This involves:
- Putting a muscle in a stretched position (also called a passive stretch) and holding for a few seconds.
- Contracting the muscle without moving (also called isometric), such as pushing gently against the stretch without actually moving. This is when the reflex is triggered and there is a “6- to the 10-second window of opportunity for a beyond ‘normal’ stretch,” Black says.
- Relaxing the stretch, and then stretching again while exhaling. This second stretch should be deeper than the first.
- Another common PNF technique is the contract-relax stretch. It is almost identical to hold-relax, except that instead of contracting the muscle without moving, the muscle is contracted while moving. This is sometimes called isotonic stretching.
- For example, in a hamstring stretch, this could mean a trainer provides resistance as an athlete contract the muscle and pushes the leg down to the floor.
- A third technique, hold-relax-contract, is similar to hold-relax, except that after pushing against the stretch, instead of relaxing into a passive stretch, the athlete actively pushes into the stretch.
- For example, in a hamstring stretch, this could mean engaging the muscles to raise the leg further, as the trainer pushes in the same direction.
- Regardless of technique, PNF stretching can be used on most muscles in the body, according to Black. Stretches can also be modified so you can do them alone or with a partner.
How to Perform PNF Stretching
- Position the muscle to be stretched in a way that it is full, but passively, stretched and under tension against an immovable object such as the floor, a wall, or with the help of a partner who can hold the limb steady.
- Perform an isometric contraction of the target muscle at full stretch. To do this, contact the stretched muscle or muscle group against the object or person, in a way that doesn’t allow any movement.
- Hold the contraction for at least ten to fifteen seconds.
- Relax the muscle briefly (about three seconds) and then move into another full, passive stretch and hold that for about 20 seconds. (You should notice your range of motion has increased slightly from your first stretch.)
- After the passive stretch, let go of any stretching and relax and rest the muscle group completely for 30 seconds.
- If desired, you can repeat the entire proprioceptive neuromuscular facilitation stretch technique another three times for the same muscle group. Some studies find that one PNF stretch session is sufficient to improve range of motion.
- Repeat in other target muscle groups as needed.
Reciprocal inhibition is what occurs in the TM when the opposing muscle is contracted voluntarily in the form of decreased neural activity in the TM. It occurs when an opposing muscle is contracted in order to maximize its contraction force, in this case, the TM relaxes. This relaxation of the TM is a result of the decrease in the neural activity, and the increase of inhibition of proprioceptive structures in the TM [rx]. Inhibition of the electrical activity in the stretched TM occurs due to the neurons’ continuation of firing in the TM, the contraction of the antagonist’s muscles would be resisted and diminished by the force of the TM continuing to receive signals to contract.
Stress relaxation is what occurs when the musculotendinous unit (MTU), which involves the muscles and the connected tendons, is under constant stress [rx]. Both muscles and tendons have viscoelastic properties in which they exhibit characteristics of both viscous and elastic materials. A viscoelastic material both resists shear flow and strain linearly when stress is applied and returns to the original form once the stress is removed from the MTU. As was mentioned before, when the MTU falls under a constant stretch, a phenomenon known as “stress relaxation” occurs. This decreases the force generated by the viscous material when it resists the elongation stimulus that stretching causes within the MTU.
The Gate Control Theory
The gate control theory is what occurs when two kinds of stimuli, such as pain and pressure, activate their respective receptors at the same time [rx]. Peripheral pain receptors are connected to either un-myelinated or small myelinated afferent fibers while pressure receptors are connected to larger myelinated afferent nerve fibers. Each type of afferent fibers connect to the same interneurons in the spine, and because the pressure afferent fibers are larger and myelinated the pressure signals make it to the spine before the pain signals do when they are stimulated simultaneously [rx]. The inhibition of the pain signals happens in the dorsal horn when the large fibers transmit signals [rx]. In CR and CRAC, when the muscle is stretched beyond its active ROM, the participant is then told to resist against this stretch, and then the TM is stretched even further. A large force and stretch is produced in the elongated muscle when the participant resists the stretch. This large force is sensed as noxious stimuli and is seen as potentially damaging, which invites the GTOs to activate in an effort to inhibit the force and prevent injury.
Effects of PNF
PNF is a stretching technique utilized to increase ROM and flexibility. PNF increases ROM by increasing the length of the muscle and increasing neuromuscular efficiency. PNF stretching has been found to increase ROM in trained, as well as untrained, individuals. Effects can last 90 minutes or more after the stretching has been completed [rx]. The duration of these effects can vary because of various things, such as changes in the percentage of MVIC asked for and the duration of the contraction of the TM during PNF stretching [rx]. PNF stretching is usually performed with a 100% MVIC, which can possibly lead to a contraction-induced injury and/or muscle soreness. Lower percentages of MVIC might reduce these risks [rx]. This contraction has been proven to produce better effects when held a total of 3–10 seconds, while six seconds is preferred [rx]. It is necessary to know why six seconds is preferred and if there is any benefit to a longer or shorter contraction.
Effects on Muscular Function
Stretching has long been viewed as beneficial to enhance performance and decrease the risk of injury during exercise, as well as improve ROM and function following an injury [rx]. PNF stretching prior to exercise has been found to decrease performance when maximal muscle effort is required such as during sprinting, plyometrics, cutting, weight-lifting and other high-intensity exercises [rx]. [rx] showed a decrease in strength, power output and muscle activation. Similar studies have shown a significant decrease in vertical jump height and power, as well as a decrease in ground reaction time and jump height, in drop jumps following PNF stretching [rx].
Although PNF may decrease performance in high-intensity exercises, it has been found to improve performance in submaximal exercises such as jogging. [rx] showed a significant increase in both stride rate and stride length after a five-week PNF stretching protocol in 18 professional rugby players.
Certain precautions need to be taken when performing PNF stretches as they can put added stress on the targeted muscle group, which can increase the risk of soft tissue injury.
- During both the stretching and the contraction phase of the PNF stretch it’s not necessary to apply maximum force or intensity. In fact, PNF stretching works best when a gentle stretch and contraction is used. Aim for a stretch intensity and a contraction force of no more than about 5 or 6 out of 10.
- The smaller the muscle group, the less force is needed. For example, if you’re stretching the small muscles in the shoulder or neck, aim for a stretch intensity and a contraction force of about 3 or 4 out of 10.
- Also, before undertaking any form of stretching it is vitally important that a thorough warm-up is completed. Warming up prior to stretching does a number of beneficial things, but primarily its purpose is to prepare the body and mind for more strenuous activity. One of the ways it achieves this is by helping to increase the body’s core temperature while also increasing the body’s muscle temperature. This is essential to ensure the maximum benefit is gained.
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