Last week I posted a boring but necessary introduction to proprioceptive neuromuscular facilitation (PNF). Here’s the link just in case you missed it or fancy a quick recap. Today we’ll look at how we go about implementing PNF stretching with reference to the literature.
What type of PNF should we use?
The agonist is the muscle group we’re looking to stretch. For example, if we want to improve dorsiflexion the plantarflexors are the agonists. The antagonist is the opposite muscle group to the agonists; in this example, the dorsiflexors. Techniques that encompass a shortening contraction of the antagonist appear to elicit greater increases in range of motion (ROM) in comparison to those using isometric activation of the agonist alone[1-2]. Activating the antagonist is commonly believed to induce reciprocal inhibition in the agonist, however, the work of Mitchell et al refutes the existence of this mechanism. Moreover, their study also refutes the existence of autogenic inhibition!
Answer: Techniques involving incorporating both agonist and antagonist activation should be utilised
When should we use PNF?
Several studies suggest that performing PNF may be harmful to subsequent strength and power performance[e.g. 4-6]. Bradley et al suggest that performance may be recovered after as little as 15 minutes, although this may still contraindicate the performance of PNF prior to activities where max strength or power is desired. It has been observed that following static stretching with dynamic warm-up may negate the potential decrements in performance associated with prolonged stretching[7-8], but this is yet to have been investigated following PNF modalities.
Answer: To facilitate correct movement incorporate PNF in the warm-up, elsewise perform as a separate session
How strong should the agonist contraction be?
The general consensus with PNF stretching previously has been to instruct maximal contraction of the agonist. It was hypothesised the greater the contraction intensity, the greater the degree of autogenic inhibition. However, research conducted by Sheard and Paine from the University of Bedfordshire suggests than an intensity of 65% MVIC (maximal voluntary isometric contraction) is optimal for eliciting increases in ROM. They hypothesised that higher intensity contractions resulted in an excitation of muscle spindle fibres that overrides the inhibition of the golgi tendon organ (GTO), should this be the overriding mechanism responsible for PNF associated enhancements, and that lower intensities do not sufficiently inhibit the GTO.
Answer: 65% of MVIC
How long should the agonist contraction be?
Recommendations for contraction duration tend to fall within the 3 to 15 seconds range. Whilst some authors have shown longer durations to elicit greater increases in ROM[e.g. 10], many have not[e.g. 11]. The review article by Sharman et al proposes that 3 seconds is therefore an effective and time efficient contraction duration.
Answer: 3 seconds appears sufficient
How many repetitions should be performed?
One repetition of PNF is sufficient to induce acute increases in ROM[e.g. 12-13]. It appears that subsequent repetitions produce minimal further gains. Considering the cost, in terms of time and effort, and the limited potential for any additional benefit, it is advised that a single repetition of PNF is performed.
Answer: One repetition of PNF appears ample
How often do we need to perform PNF?
The Sharman review highlights that previous studies have observed PNF-induced increases in ROM to drop off quickly following cessation of the intervention. The authors recommend that PNF is performed once or twice a week and, importantly, that ROM is regularly reassessed to determine if this frequency is sufficient.
Answer: At least once a week
Whilst we still don’t fully understand the mechanisms behind PNF stretching, the recommendations outlined above would appear to elicit the greatest increases in ROM with the least amount of time and effort. Whilst this may all look great on paper, it is unlikely this procedure would be optimal in every instance. Look at this article as a template for incorporating PNF and adjust the variables as you see fit.
1. Osternig LR, Roberston RN, Troxel RK, et al. (1990). Differential responses to proprioceptive neuromuscular facilitation (PNF) stretch techniques. Medicine and Science in Sports and Exercise 22(1): 106-11
2. Ferber R, Osternig L, Gravelle D. (2002). Effect of PNF stretch techniques on knee flexor muscle EMG activity in older adults. Journal of Electromyography and Kinesiolology 12(5): 391-7
3. Mitchell UH, Myrer JW, Hopkins TY, et al. (2009). Neurophysiological reflex mechanisms’ lack of contribution to the success of PNF stretches. Journal of Sport Rehabilitation 18(3): 343-357
4. Marek SM, Cramer JT, Fincher AL, et al. (2005). Acute effects of static and proprioceptive neuromuscular facilitation stretching on muscle strength and power output. Journal of Athletic Training 40(2): 94-103
5. Bradley PS, Olsen PD, Portas MD. (2007). The effect of static, ballistic, and proprioceptive neuromuscular facilitation stretching on vertical jump performance. Journal of Strength and Conditioning Research 21(1): 223-226
6. Miyahara Y, Naito H, Ogura Y, et al. (2012). Effects of proprioceptive neuromuscular facilitation stretching and static stretching on maximal voluntary contraction. Journal of Strength and Conditioning Research, Mar 3 [Epub ahead of print]
7. Taylor KL, Sheppard JM, Lee H, et al. (2009). Negative effect of static stretching restored when combined with a sport specific warm-up component. Journal of Science and Medicine in Sport 12(6): 657-661
8. Chaouachi A, Castagna C, Chtara M, et al. (2010). Effect of warm-ups involving static or dynamic stretching on agility, sprinting, and jumping performance in trained individuals. Journal of Strength and Conditioning Research 24(8): 2001-11
9. Sheard PW, Payne TJ (2010). Optimal contraction intensity during proprioceptive neuromuscular facilitation for maximal increase of range of motion. Journal of Strength and Conditioning Research 24(2): 416-421
10. Rowlands AV, Marginson V, Lee J. (2003). Chronic flexibility gains: effect of isometric contraction duration during proprioceptive neuromuscular facilitation stretching techniques. Res Quarterly for Exercise and Sport 74(1): 47-52
11. Bonnar BP, Deivert RG, Gould TE. (2004). The relationship between isometric contraction durations during hold-relax stretching and improvement of hamstring flexibility. Journal of Sports Medicine and Physical Fitness 44 (3): 258-61
12. Sharman MJ, Cresswell AG, Riek S. (2006). Proprioceptive neuromuscular facilitation stretching: mechanisms and clinical implications. Sports Medicine 36(11): 929-39
13. O’Hora, J, Cartwright, A, Wade, CD, et al. (2011). Efficacy of static stretching and proprioceptive neuromuscular facilitation stretch on hamstrings length after a single session. Journal of Strength and Conditioning Research 25(6): 1586-1591