Context: Stretching is commonly used as a technique for injury prevention in the clinical setting. Our findings may improve the understanding of the neuromuscular responses to stretching and help clinicians make decisions for rehabilitation progression and return to play.Objective: To examine the short-term effects of static and proprioceptive neuromuscular facilitation stretching on peak torque (PT), mean power output (MP), active range of motion (AROM), passive range of motion (PROM), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis and rectus femoris muscles during voluntary maximal concentric isokinetic leg extensions at 60 and 300 degrees .s.Design: A randomized, counterbalanced, cross-sectional, repeated-measures design.Setting: A university human research laboratory.Patients or Other Participants: Ten female (age, 23 +/- 3 years) and 9 male (age, 21 +/- 3 years) apparently healthy and recreationally active volunteers.Intervention(s): Four static or proprioceptive neuromuscular facilitation stretching exercises to stretch the leg extensor muscles of the dominant limb during 2 separate, randomly ordered laboratory visits.Main Outcome Measure(s): The PT and MP were measured at 60 and 300 degrees .s, EMG and MMG signals were recorded, and AROM and PROM were measured at the knee joint before and after the stretching exercises.Results: Static and proprioceptive neuromuscular facilitation stretching reduced PT (P = .051), MP (P = .041), and EMG amplitude (P = .013) from prestretching to poststretching at 60 and 300 degrees .s (P .05).Conclusions: Both static and proprioceptive neuromuscular facilitation stretching caused similar deficits in strength, power output, and muscle activation at both slow (60 degrees .s) and fast (300 degrees .s) velocities. The effect sizes, however, corresponding to these stretching-induced changes were small, which suggests the need for practitioners to consider a risk-to-benefit ratio when incorporating static or proprioceptive neuromuscular facilitation stretching.

Acute Effects of Static and Proprioceptive Neuromuscular Facilitation Stretching on Muscle Strength and Power Output.

Proprioceptive neuromuscular facilitation (PNF) stretching techniques are commonly used in the athletic and clinical environments to enhance both active and passive range of motion (ROM) with a view to optimising motor performance and rehabilitation. PNF stretching is positioned in the literature as the most effective stretching technique when the aim is to increase ROM, particularly in respect to short-term changes in ROM. With due consideration of the heterogeneity across the applied PNF stretching research, a summary of the findings suggests that an 'active' PNF stretching technique achieves the greatest gains in ROM, e.g. utilising a shortening contraction of the opposing muscle to place the target muscle on stretch, followed by a static contraction of the target muscle. The inclusion of a shortening contraction of the opposing muscle appears to have the greatest impact on enhancing ROM. When including a static contraction of the target muscle, this needs to be held for approximately 3 seconds at no more than 20% of a maximum voluntary contraction. The greatest changes in ROM generally occur after the first repetition and in order to achieve more lasting changes in ROM, PNF stretching needs to be performed once or twice per week. The superior changes in ROM that PNF stretching often produces compared with other stretching techniques has traditionally been attributed to autogenic and/or reciprocal inhibition, although the literature does not support this hypothesis. Instead, and in the absence of a biomechanical explanation, the contemporary view proposes that PNF stretching influences the point at which stretch is perceived or tolerated. The mechanism(s) underpinning the change in stretch perception or tolerance are not known, although pain modulation has been suggested.

Proprioceptive neuromuscular facilitation stretching : mechanisms and clinical implications.

Stretching is a common activity used by athletes, older adults, rehabilitation patients, and anyone participating in a fitness program. While the benefits of stretching are known, controversy remains about the best type of stretching for a particular goal or outcome. The purpose of this clinical commentary is to discuss the current concepts of muscle stretching interventions and summarize the evidence related to stretching as used in both exercise and rehabilitation.

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Current concepts in muscle stretching for exercise and rehabilitation

Proprioceptive neuromuscular facilitation (PNF) is common practice for increasing range of motion, though little research has been done to evaluate theories behind it. The purpose of this study was to review possible mechanisms, proposed theories, and physiological changes that occur due to proprioceptive neuromuscular facilitation techniques. Four theoretical mechanisms were identified: autogenic inhibition, reciprocal inhibition, stress relaxation, and the gate control theory. The studies suggest that a combination of these four mechanisms enhance range of motion. When completed prior to exercise, proprioceptive neuromuscular facilitation decreases performance in maximal effort exercises. When this stretching technique is performed consistently and post exercise, it increases athletic performance, along with range of motion. Little investigation has been done regarding the theoretical mechanisms of proprioceptive neuromuscular facilitation, though four mechanisms were identified from the literature. As stated, the main goal of proprioceptive neuromuscular facilitation is to increase range of motion and performance. Studies found both of these to be true when completed under the correct conditions. These mechanisms were found to be plausible; however, further investigation needs to be conducted. All four mechanisms behind the stretching technique explain the reasoning behind the increase in range of motion, as well as in strength and athletic performance. Proprioceptive neuromuscular facilitation shows potential benefits if performed correctly and consistently.

https://www.degruyter.com/downloadpdf/j/hukin.2012.31.issue--1/v10078-012-0011-y/v10078-012-0011-y.xml

Proprioceptive Neuromuscular Facilitation (PNF): Its Mechanisms and Effects on Range of Motion and Muscular Function

INTRODUCTION: Warm-up and stretching may increase flexibility and reduce injury risk, yet there is disagreement on the benefits of stretching and which technique is best (Thacker et al 2004). This study examined the short-term effects of warm-up, static and dynamic stretching on hamstring flexibility in individuals with previous hamstring injury and uninjured controls. METHOD: A randomised crossover study was performed over 2 days. Hamstring flexibility was assessed in supine using passive knee extension range of motion (PKE ROM). The reliability of assessing PKE ROM using a ‘Myrin’ goniometer, with a crossbar maintaining the hip at 90◦ flexion, was examined in a preliminary pilot study (n= 25) and was excellent (ICC = 0.945, SEM 1.84◦). 36 individuals (18 injured, 18 controls) participated. Only previously injured subjects who were now painfree, but with a residual reduction of 5◦ of PKE ROM compared to the other leg were included. On both days, four measurements of PKE ROM were recorded: (1) at baseline; (2) after a 5-minute aerobic warm-up; (3) after stretch (static or dynamic) and (4) after a 15-minute rest. Both stretches were performed for 30 seconds and repeated 3 times for each leg. Participants carried out both static and dynamic stretches, but on different days. Data were analysed using a 1-way repeated measures anova. RESULTS: Across both groups, there was no interaction effect (p=0.344). There was a significant main effect for time (p 0.05). Using ANCOVA to adjust for the non-significant (p=0.141) baseline differences, the previously injured group demonstrated a greater response to warm-up and static stretching, which was not statistically significant (p=0.05) DISCUSSION: Warm-up significantly increased hamstring flexibility. Static stretching also increased hamstring flexibility, whereas dynamic did not, in agreement with previous findings on uninjured controls. The greater effect of warm-up and static stretching on flexibility in those with reduced flexibility post-injury is worthy of further study. CONCLUSION: Further prospective research is required to validate the hypothesis that increased flexibility improves injury or performance outcomes, as this study only examined short-term flexibility. The results contrast with research demonstrating the greater benefits of dynamic stretching on performance measures. There may be a need to consider both forms of stretching during training and rehabilitation, but for different purposes. REFERENCES: Thacker, SB, Gilchrist, J, Stroup, DF and Dexter, C (2004) The Impact of Stretching on Sports Injury Risk: A Systematic Review of the Literature. Medicine and Science in Sports and Exercise 36, 371-378.

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The effect of warm-up, static stretching and dynamic stretching on hamstring flexibility

Position stands from the American College of Sports Medicine and the Surgeon General site a need for strategies capable of enhancing the effectiveness of stretching on flexibility and joint range of motion One strategy for enhancing flexibility that has received anecdotal support but lacks substantial experimental evidence is the impact of prior exercise This study compared 5 minutes of static stretching and proprioceptive neuromuscular facilitation (PNF) on hamstring flexibility performed with and without exercise Forty undergraduate student-athletes participated in a repeated measure, counterbalanced experimental design Within-group comparisons indicated that PNF resulted in a significant (p < 005) increase in flexibility after 60 minutes of exercise when compared with baseline (96%) and without exercise (78%) No differences were observed with static stretching across time In addition, no differences were observed between the groups at any time point Results demonstrated that PNF performed after exercise enhanced acute hamstring flexibility, and implementing a PNF stretching routine following exercise may augment current stretching practices among athletes

Brian K. Farr

Papers

Impact of prior exercise on hamstring flexibility: a comparison of proprioceptive neuromuscular facilitation and static stretching.