Clinical Pearl: PNF Hamstring Stretching

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The hamstring muscle group is very important for athletic and dynamic activities; a shortened, or less elastic muscle, can be associated with trigger points/hypertonicity or quadricep-hamstring muscle imbalances that give an increased risk for injury. Proprioceptive neuromuscular facilitation (PNF) is widely accepted for increasing both active range of motion (AROM) and passive range of motion (PROM), specifically for short-term periods (Sharman). PNF is thought to be more beneficial than static stretching due to the activation of the musculotendinous unit (MTU) along with showing greater ROM changes (Gunn; Konrad)

The complete physiological understanding behind PNF is still unknown, but it is theorized that autogenic inhibition and reciprocal inhibition are responsible (Sharman). Facilitated by autogenic inhibition, there is a reduction in the efferent (motor) input to a muscle through isometric contraction while placed on a stretch which modulates the hypertonicity (Sharman). Reciprocal inhibition, in a similar way as the previous, inhibit the afferent (receptors within the muscle) path of the agonist muscle through contraction of the antagonist (Sharman). Both of these mechanisms explain the short-term, immediate effects on muscle extensibility seen after PNF; however, improved joint range was seen using PNF rehabilitation programs (Konrad; Minshull). Patients were instructed to use a PNF stretching program five times per week for six weeks and demonstrated significant increased dorsiflexion ROM (Konrad). Similarly, during an eight-week rehabilitation program using PNF three times per week, improvements of flexibility were recorded compared to a control limb (Minshull). These long-term effects after a PNF intervention cannot be explained using autogenic or reciprocal inhibition which suggests that other physiological processes are taking place.

The procedures of PNF stretching involve a target muscle (TM) and an opposing muscle (OM). There are multiple techniques that center around stretching and activating a series of muscles; the particular skills under review involve isometric contraction holds of the TM at 20% of the patient’s maximum voluntary contraction for 6-10 seconds followed by relaxation and a new barrier ROM repeated 3-4 times. A hold-relax technique- passive stretching of the TM followed by static contraction of TM1- targets more of the hamstring muscle belly. Figure 1 shows the clinician passively flexes hip and instructs patient to curl toes, point foot, and bring whole leg back down into the table against resistance; patient relaxes after 6-10 seconds and a new barrier is met. A contract-relax-contract technique (see figure 2) can be used to address the more proximal hamstring and involves OM shortening contraction to place TM into stretch (Sharman). The patient pulls hip into maximum flexion; keeping that position, the patient extends knee to as much ROM as achievable while keeping hip in previous amount of flexion; clinician instructs the patient to curl toes, point foot, and dig heel into the clinicians palm of hand against resistance; patient relaxes after 6-10 seconds, knee extension relaxes, and patient pulls leg into a new degree of hip flexion.

In functional testing (active straight leg raise) of hip flexion range of motion (ROM), PNF stretching significantly improved immediate passive and active hip flexion ROM (95% CI) when compared to static stretching alone (Gunn). Additionally, a 6-week stretching program showed similar results with PNF stretching increasing gastrocnemius ROM while also decreasing Achilles tendon stiffness (P=0.02 and P=0.01 respectively) (Konrad).

Figure 1. Hold-Relax: patient curls toes, points foot, and isometrically contracts hamstring complex extending hip back down into the table against resistance.

Figure 2. Contract-Relax-Contract: patient pulls hip into maximum flexion, extends knee; clinician instructs the patient to curl toes, point foot, and dig heel into the clinician’s palm of hand against resistance.

Citation:

1. Sharman MJ, Cresswell AG, Riek S. Proprioceptive neuromuscular facilitation stretching : mechanisms and clinical implications. Sports Med. 2006;36(11):929-939.

2. Gunn LJ, Stewart JC, Morgan B, et al. Instrument-assisted soft tissue mobilization and proprioceptive neuromuscular facilitation techniques improve hamstring flexibility better than static stretching alone: a randomized clinical trial. J Man Manip Ther. 2019;27(1):15-23.

3. Konrad A, Gad M, Tilp M. Effect of PNF stretching training on the properties of human muscle and tendon structures. Scand J Med Sci Sports. 2015;25(3):346-355.

4. Minshull C, Eston R, Bailey A, Rees D, Gleeson N. The differential effects of PNF versus passive stretch conditioning on neuromuscular performance. Eur J Sport Sci. 2014;14(3):233-241.