Effect of PNF stretch techniques on knee flexor muscle EMG activity in older adults

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Abstract

The effects of proprioceptive neuromuscular facilitation (PNF) stretch techniques on older adults are unknown and the physiological changes associated with aging may lead to differential responses to PNF stretching. Therefore, the purpose of this experiment was to examine the effects of PNF stretch techniques and EMG activity in older adults. Three PNF stretch techniques: static stretch (SS), contract–relax (CR), and agonist contract–relax (ACR) were applied to 24 older adults aged 50–75 years. The subjects were tested for knee extension range of motion (ROM) and knee flexor muscle EMG activity. The results indicated that ACR produced 29–34% more ROM and 65–119% more EMG activity than CR and SS, respectively. It was concluded that PNF stretch techniques can increase ROM in older adults. However, a paradoxical effect was observed in that PNF stretching may not induce muscular relaxation even though ROM about a joint increases. Care should be taken when applying PNF stretch techniques to older adults due to age-related alterations in muscle elasticity.

Introduction

Proprioceptive neuromuscular facilitation (PNF) techniques make use of proprioceptive stimulation for the strengthening (facilitation) or relaxation (inhibition) of particular muscle groups [1], [2]. One principle of PNF maintains that voluntary muscular contractions are performed in combination with muscle stretching to reduce the reflexive components of muscular contraction, promote muscular relaxation, and subsequently increase joint range of motion (ROM) [1], [3]. PNF stretch techniques have been demonstrated to increase joint range of motion as compared to non-PNF stretch techniques [4], [5]. Tanigawa [4] compared PNF stretch techniques to passive mobilization and reported that the PNF procedure resulted in greater gains in ROM. Sady et al. [5] compared PNF, static, and ballistic stretch techniques on shoulder, trunk, and hamstring muscles and reported that the PNF stretch procedures achieved significantly greater gains in ROM at all three joints compared to the other stretch techniques.

Resistance to musculotendinous stretching involves both the mechanical viscoelastic properties of muscle and connective tissue, as well as the neurological reflexive and voluntary components of muscular contractions [6], [7], [8], [9]. PNF stretch techniques are believed to reduce reflexive components that stimulate muscular contraction and thereby enable joint range of motion to increase [3]. However, few studies have provided neurophysiological evidence as to the effectiveness of PNF stretch techniques [6], [7], [8], [9]. In contrast to the theoretical basis, previous investigations have also shown that while PNF techniques achieve a gain in ROM, electromyographic (EMG) activity in the muscle being stretched is not necessarily reduced and in some cases is actually increased [6], [7], [8], [9]. These studies suggest a paradoxical ROM/muscle tension relationship in that PNF stretching may not induce muscular relaxation even though ROM about a joint increases.

Little is known about the effects of PNF as a method to increase joint ROM on older adults. Ferber et al. [10] examined the effects of PNF stretch techniques in trained and untrained older adults and reported that PNF stretch techniques can be used to increase knee joint extension ROM in older adult populations depending on activity level and age. However, these authors did not measure knee flexor EMG activity and the effects of PNF stretch techniques on muscle EMG activity in older adults remains unclear.

It has been reported that biological changes associated with aging are related to a loss of joint range of motion in individuals past the fourth decade of life [11], [12], [13], [14], [15]. These individuals have also been demonstrated to exhibit increased muscle stiffness [16], [17], muscle atrophy [18], increases in type I collagen [19] as well as a reorganization of the motor unit [20]. In light of these changes, older adults may demonstrate a differential response to increases in joint ROM and muscle EMG activity during the application of PNF stretch techniques compared to young adults. Therefore, the purpose of this experiment was to examine the effects of PNF stretch techniques on knee joint ROM and EMG activity in older adults. Based on the physiological changes that occur in individuals past the fourth decade of life, it was hypothesized that older adults would exhibit no differences in joint ROM or muscle EMG between the three PNF stretch techniques.

Section snippets

Subjects

Twenty-six male subjects (55–75 yr) volunteered to participate in the study. All subjects were healthy, active older adults partaking in low-intensity health-maintenance activities such as golf, walking, and gardening. No subject had a prior history of lower extremity infirmity or pathology within the year prior to testing or at the time of testing and none was suffering from osteoarthritic or musculoskeletal disease that may have affected the ability to perform the tests. No subject was

Results

An overall effect of stretch condition on ROM (F2,23 = 17.34, p<0.05) and hamstring (F2,23 = 21.99, p<0.05) and gastrocnemius (F2,23 = 23.68, p<0.05) EMG was observed (Fig. 2, Fig. 3). The ACR–PNF stretch condition produced the greatest gains in knee joint extension ROM as well as the greatest increase in knee flexor muscle EMG activity compared to CR and SS (Fig. 2, Fig. 3). The average ROM produced during the ACR–PNF stretch procedure was 15.66±0.95° and was significantly greater than SS

Discussion

The purpose of this study was to examine the effects of PNF stretch techniques on knee joint ROM and EMG activity in older adults. Based on the physiological changes that occur in individuals past the fourth decade of life, it was hypothesized that older adults would exhibit no differences in joint ROM or muscle EMG between the three PNF stretch techniques. In contrast to the hypotheses, an overall significant effect of condition was observed in that the ACR–PNF condition resulted in 29% and

Conclusion

PNF stretch techniques can be used to increase ROM in older adult populations. In addition, older adults exhibit a similar response to PNF stretch techniques as compared to previous literature involving younger adults in that the ACR–PNF stretch technique achieved greater knee joint ROM and muscle EMG activity compared to the CR and SS stretch conditions.

Acknowledgements

Portions of this work were presented at the 45th American College of Sports Medicine Annual Meeting, Orlando, FL, USA, 1998 and the 24th Annual Meeting of the American Orthopaedic Society for Sports Medicine, Vancouver, Canada, 1998.

Reed Ferber received a Ph.D. in Biomechanics from the University of Oregon. He currently serves as a Post-Doctoral Fellow for the Motion Analysis Laboratory in the Department of Physical Therapy at the University of Delaware. His current research interests include adaptations to anterior cruciate ligament injury and surgery, the etiology of stress fractures in runners, and gender differences in running mechanics.

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    Reed Ferber received a Ph.D. in Biomechanics from the University of Oregon. He currently serves as a Post-Doctoral Fellow for the Motion Analysis Laboratory in the Department of Physical Therapy at the University of Delaware. His current research interests include adaptations to anterior cruciate ligament injury and surgery, the etiology of stress fractures in runners, and gender differences in running mechanics.

    Louis Osternig received a Ph.D. from the University of Oregon and currently is Professor and Head of Graduate Studies in the Department of Exercise and Movement Science at the University of Oregon. His current research includes neuromuscular adaptations to anterior cruciate ligament injury and surgery, and multi-joint accommodations to knee arthritis and total knee replacement.

    Denise Gravelle received a MS in Biomechanics in the Department of Exercise and Movement Science at the University of Oregon. She is currently a research engineer for the Center for BioDynamics in the Department of Biomedical Engineering at Boston University. Her current research interests include human postural control and sensory enhancement.

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