ARTICLE IN PRESS Journal of Bodywork and Movement Therapies (2008) 12, 312–317
Journal of Bodywork and Movement Therapies www.elsevier.com/jbmt
CLINICAL METHODS STUDY
A comparison of two muscle energy techniques for increasing flexibility of the hamstring muscle group Madeleine Smith, B.Clin.Sc., M.H.Sc.(Osteo)a, Gary Fryer, Ph.D., B.App.Sc.(Osteo.), N.Da,b,c, a
School of Biomedical and Clinical Sciences, Victoria University, Melbourne, Australia Centre for Ageing, Rehabilitation & Exercise Science, Victoria University, Melbourne, Australia c A. T. Still Research Institute, A. T. Still University of Health Sciences, 800 W. Jefferson St., Kirksville, MO 63501, USA b
Received 17 April 2008; received in revised form 15 June 2008; accepted 17 June 2008
KEYWORDS Muscle; Hamstring; Stretching; Isometric; Osteopathic medicine
Summary Variations in the application of muscle energy technique (MET) for increasing the extensibility of muscles have been advocated, but little evidence exists to support the relative merit of a particular approach. This study investigated two types of muscle energy techniques that have been advocated in the osteopathic literature that differ primarily in the duration of the post-contraction stretch phase. Forty asymptomatic participants (mean age ¼ 22.173.5, male female ¼ 1:4) were randomly allocated to one of two groups (Group 1: MET with 30-s post-isometric stretch phase; Group 2: MET with 3-s post-isometric stretch phase). Hamstring length was measured using active knee extension (AKE). Participants received an initial application of the allocated intervention, and then a second application 1 week later. Analysis with a split-plot ANOVA revealed a significant effect of time (F3,36 ¼ 42.30;po0.01), but no significant time*group interaction (F3,36 ¼ 0.12; p ¼ 0.95). Post-hoc analysis revealed that the significant differences over time occurred between pre- and post-measurements at both weeks, and between postWeek 1 and pre-Week 2 measurements. Both techniques appeared to be equally effective in increasing hamstring extensibility, and there appeared to be sustained improvement 1 week following the initial treatment. The findings suggest that altering the duration of the passive stretch component does not have a significant impact on the efficacy of MET for short-term increases in muscle extensibility. & 2008 Elsevier Ltd. All rights reserved.
Corresponding author at: A. T. Still Research Institute, A. T. Still University of Health Sciences, 800 W. Jefferson St., Kirksville, MO
63501, USA. Tel. +1 660 626 2530 Fax: +1 660 626 2099. E-mail address: gfryer@atsu.edu (G. Fryer). 1360-8592/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbmt.2008.06.011
ARTICLE IN PRESS A comparison of two muscle energy techniques for increasing flexibility
Introduction Muscle energy technique (MET) is a manual procedure that uses controlled, voluntary isometric contractions of a targeted muscle group and is widely advocated by authors in the field of osteopathy. MET is claimed to be useful for lengthening a shortened muscle, improving range of motion at a joint and increasing drainage of fluid from peripheral regions (Greenman, 2003). Muscle energy procedures, and related post-isometric procedures such as proprioceptive neuromuscular facilitation (PNF), have been demonstrated to be more effective than static stretching for improving the extensibility of shortened muscles (Handel et al., 1997; Magnusson et al., 1996a; Sady et al., 1982). Passive stretching of various muscle groups, particularly the hamstrings, has been reported to improve the length and extensibility of muscles in both short and long-term periods of stretching (Bandy et al., 1997; Bandy et al., 1994; Feland et al., 2001; Roberts and Wilson, 1999). Additionally, many researchers have reported that postisometric stretching techniques, such as MET and PNF, produce greater changes in range of motion and muscle extensibility than static or ballistic stretching, immediately following treatment (Cornelius et al., 1992; Moore and Hutton, 1980; Tanigawa, 1992; Wallin et al., 1985) and in the longer term (Handel et al., 1997; Magnusson et al., 1996a; Sady et al., 1982; Wallin et al., 1985). The exact mechanism by which increased muscle extensibility occurs is still unclear, and probably involves both neurophysiological (including changes to stretch tolerance) and mechanical factors (such as viscoelastic and plastic changes in the connective tissue elements of the muscle) (Fryer, 2006). Although there are many variations of the application of MET, with most authors in the field of osteopathy advocating a post-isometric stretch for increasing muscle length, the recommended duration for the passive stretch component varies. A typical application of MET for the purpose of lengthening a shortened muscles involves the following steps: (1) stretch the muscle to a palpated ‘barrier’ or to the patient’s tolerance of stretch, (2) the patient produces a voluntary isometric contraction of the muscle under stretch against the clinicians’ controlled and equal counterforce, (3) the muscle is allowed to relax, while the clinician maintains a stretch for a defined period, (4) the clinician ‘takes up the slack’ following relaxation so that the muscle has been lengthened to a new barrier, (5) this process is repeated several times. It is possible to alter the
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application of MET by with variations to the components of the technique: the force and duration of the isometric contraction phase, the duration of the post-contraction stretch phase, and the number of repetitions. The literature currently offers little guidance as to the most efficacious application (Fryer, 2006). In the osteopathic literature, two markedly different applications of MET for increasing muscle extensibility have been advocated by Greenman (2003) and Chaitow (2006), with differences in the number of repetitions (3–5 and 3, respectively), and the period of passive stretching between the isometric contractions. Chaitow suggests a stretch duration following isometric contraction to be held for at least 30 and up to 60 s for chronically shortened muscles, whereas Greenman (2003) and Mitchell et al. (1979) recommend only enough time (several seconds) for patient relaxation and tension to be taken up in the affected tissue. The relative merit and efficacy of these different approaches have not been investigated. Ballantyne et al. (2003) and Lenehan et al. (2003) used techniques similar to the Greenman protocol, both following a 5–7 isometric contraction with a passive stretch lasting only several seconds until the new barrier was engaged. Other researchers have used PNF techniques similar to the Chaitow method, such as Wallin et al. (1985) and Handel et al. (1997), who used a maximal isometric contraction with a 15 s rest period. While these techniques were similar to the method advocated by Chaitow, the duration of the stretch (15 s) was shorter than the recommended minimum of 30 s (Chaitow, 2006). The longer passive stretch of the Chaitow approach may make the technique more effective, given that passive stretching for a 30-s (Bandy and Irion 1994) or 60-s (Feland et al., 2001) period have been reported to be more efficacious for increasing muscle extensibility than shorter durations. The relative efficacy of the Greenman and Chaitow approaches for increasing myofascial extensibility should be investigated. Most research involving MET has focused on a single application of treatment (Ballantyne et al., 2003; Mehta and Hatton, 2002; Magnusson et al., 1996a), but practitioners typically deliver more than one treatment for a patient complaint, and anticipate that there will be carry-over changes still present from the previously delivered treatment. This study aimed to determine the relative efficacy of the two approaches for increasing the extensibility of the hamstring muscles, and determine if there were any carry-over changes in hamstring length, or changes in responsiveness to treatment, when the
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hamstrings were treated on a second occasion 1 week later.
Materials and methods Participants Forty participants (mean age ¼ 22.173.5 years, male: female ¼ 1.4) were recruited from students enrolled at Victoria University, Melbourne, Australia. Twenty participants were required for each group to achieve 80% power, based on a large effect size, and analysis using a split-plot ANOVA (SPANOVA) (Aron and Aron, 1999). Volunteers under the age of 18 and over the age of 65 were excluded, as were those with lower extremity or lower back pain at the time of the study. Participants were included if they presented with shortened hamstrings, determined as o751 of active knee extension (AKE). Volunteers with 4751 of AKE were excluded from the study, resulting in 15 volunteers (mean age ¼ 22 years, SD ¼ 1.4, male: female ratio of 0.15) being excluded. Written, informed consent was obtained from all participants and the study was approved by the Victoria University Human Research Ethics committee. Participants were randomly assigned to Group 1 (MET with 30-s stretch) (N ¼ 20; mean age ¼ 21 years, SD ¼ 2.0; male: female ratio ¼ 1.2) or Group 2 (MET with 3-s stretch) (n ¼ 20; mean age ¼ 23.2 years, SD ¼ 4.7; male: female ratio ¼ 1.5).
Figure 1 Active knee extension measurement.
Pilot reliability study An AKE pilot reliability study was conducted on 15 participants using 2 measurements of AKE, 10 min apart, where the participant remained positioned and attached to stabilsing bar in order to establish an accurate measure of the reliability of the measurement procedure. Repeatability was determined using an intra-class correlation (ICC) and found to be highly correlated (ICC ¼ 0.99). The standard error of mean (SEM) for the difference scores between the two trials, which reflects the variability of measurements due to repetition and random error and provides an indication of the absolute reliability of the measurement procedure, was calculated to be 0.79.
Measures AKE was used to measure hamstring extensibility. AKE has been commonly used by researchers for the measurement of hamstring length (Handel et al., 1997) and has been demonstrated to be a reliable measure (Sullivan et al., 1992). The participants were requested to lie supine and the experimental hip flexed to 901 and strapped to a stabilizing bar. The thigh of the opposite leg was firmly secured to minimize rotation of the pelvis (Sullivan et al., 1992). Joint markers were placed on the greater trochanter, lateral femoral condyle, head of the fibula and lateral malleolus to provide a point of reference to measure degree of knee extension (Figure 1). The participants were asked to extend the knee as far as possible, and a photograph was taken of this position using a digital camera by Researcher 1. This procedure was performed three times. The digital images were analyzed using ‘‘SiliconCOACH Pro’’ software to determine the angle of AKE, and the mean of the three measures used for analysis.
Procedure Researcher 1 measured the AKE of the investigated leg and then left the room. Researcher 2 (GF; a registered osteopath with 15 years clinical experience) entered the room and assigned participants to treatment groups via lottery draw. Researcher 2 (MS; a final-year osteopathic student) treated the experimental leg of the participants according to the group allocation (Figure 2), and then left the room. Researcher 1, who was blinded to the treatment allocations, re-entered the room and performed the post-treatment AKE measurement All participants returned 1 week later, receiving the same measurement and treatment procedure as previously described. There were no restrictions to participant activity between treatments. Intervention Subjects allocated to Group 1 (n ¼ 20; mean age ¼ 21, SD ¼ 2; male: female ¼ 1:2) received
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Statistical significance was set at the po0.05 level. Post-hoc analysis for significant differences between the time periods were conducted with paired t-tests.
Results
an application of MET as advocated by Chaitow (2006): the supine subject’s hip was passively flexed and the leg extended until tension was sensed by the researcher and the subject reported a moderate stretching sensation. The participant provided a moderate (approximately 40% of maximal contraction) knee flexion isometric contraction, against the researcher’s shoulder for 7–10 s. This was followed by 2–3 s of relaxation, and then the leg was passively stretched to the palpated barrier and/or tolerance to stretch and held for 30 s. The leg was then lowered to the table for a short resting period (approximately 10 s). This procedure was repeated two more times. Those subjects allocated to Group 2 (n ¼ 20; mean age ¼ 23.2, SD ¼ 4.7; male: female ¼ 1:5) received an application of MET as advocated by Greenman (2003): the supine subject’s hip was passively flexed and the leg extended until tension was sensed by the researcher and the subject reported a moderate stretching sensation. The participant then provided a moderate (approximately 40% of maximal contraction) knee flexion isometric contraction against the researcher’s shoulder for 7–10 s. The subject was allowed to relax for 2–3 s with the stretch maintained, and then the leg was further extended to the palpated barrier and/or tolerance to stretch. This procedure was repeated three more times.
Analysis All data were collated and analyzed using SPSS professional version 16. Pre- and post-intervention ROM measurements were analyzed for both groups using a multi-variate (Hotelling’s T) SPANOVA.
Table 1
Mean AKE values (SD) for MET groups
Week Treatment PrePosttreatment treatment
Pre–post
1
2
Group 1
154.00
8.484
Group 2
145.52 (8.64) 142.23
150.23
7.89
Group 1 Group 2
147.62 145.12
153.7 151.48
6.05 6.37
Treatment Allocation Group 1
155.00
Group 2 152.50 Average AKE
Figure 2 Application of muscle energy technique.
The means and standard deviations for each measurement period (pre-treatment, posttreatment and pre–post) are shown in Table 1 and Figure 3. Pre–post gains were similar for both Groups 1 and 2 at Week 1 (8.48 and 7.89) and Week 2 (6.05 and 6.37) (Table 2). Analysis with the SPANOVA revealed a significant effect of time (F3,36 ¼ 42.30; po0.01), but no significant time*group interaction (F3,36 ¼ 0.12; p ¼ 0.95). Further post-hoc analysis of the entire group over each time interval using paired t tests revealed significant differences between Week 1 pre-measurement and all other measurement
150.00
147.50
145.00
142.50 Week 1 Pre PPT
Week 1 Post PPT
Week 2 Pre PPT
Week 2 Post PPT
Treatment Time
Figure 3 Comparative means of AKE (degrees) over time.
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Table 2
Post-hoc analysis of changes over time
Treatment phase
Mean (SD)
Week Week Week Week Week Week
8.24 2.49 8.70 5.75 .46 6.21
1 1 1 1 1 2
pre–post pre—Week 2 pre pre—Week 2 post post—Week 2 pre post—Week 2 post pre—Week 2 post
(4.89) (7.19) (9.15) (7.85) (8.68) (4.99)
p-value 0.00 0.04 0.00 0.00 0.74 0.00
periods, and between Week 1 post- and Week 2 pretreatment measurements, and between Week 2 pre- and post-measurements, suggesting both short- and long-term significant changes in AKE (Table 2).
Discussion Many variations of post-isometric stretching have been advocated for the lengthening of shortened muscles, but little research is available to help clinicians choose the most efficacious method. Although a few researchers have examined the effect of varying the application of certain components in these techniques (Feland and Marin, 2004; Mehta and Hatton, 2002; Rowlands et al., 2003), little can yet be concluded concerning the most efficacious application. A direct comparison between the methods advocated by Chaitow and Greenman, two of the most commonly advocated approaches to muscle stretching in the osteopathic literature, had not previously been investigated. The present study found that the immediate pre–post comparison of AKE at both treatment periods were significantly increased, demonstrating an increase in the extensibility of the hamstring muscle group. Although there was a significant within-group change over time, no significant differences were evident between the two treatment groups. Neither method in the present study was found to produce significantly greater gains in range of motion on either treatment day or between treatment days, suggesting that both treatment techniques were equally effective for increasing range of motion. This in itself is an important finding, and implies that while MET may be more effective than static stretching (Handel et al., 1997; Magnusson et al., 1996a; Sady et al., 1982), variations in the duration of post-isometric stretch do not significantly alter the efficacy for increasing muscle length. However, it is worth noting that the Greenman approach may be more time efficient because the period between contractions is substantially shorter.
In the present study, the two treatments were separated by a period of 1 week, and there was a significant difference between the initial preintervention values and both the pre- and postintervention values of the second week. While only two treatments in 8 days is not representative of typical clinical practice, the results suggest a carryover effect from the first treatment. These results also suggest that a longer period of treatment may produce further gains in range of motion, and this is worthy of investigation in the future. Bandy and Irion (1994) explored the effect of variations in the duration of each individual stretch over a series of treatments, and found that a 30-s duration of passive stretching produced increases in range of motion greater than shorter durations, but no different from longer ones. This suggests that the longer passive stretch of the Chaitow approach (30–60 s) may make the technique more efficacious. This was not demonstrated, however, in the present study. It may be that application over a longer period of treatment, such as the 8 weeks used by Bandy and Irion (1994), may be needed to demonstrate differences in the efficacy of the two techniques for increasing muscle extensibility, and this is an area that should be further investigated. The mechanism of action of isometric contraction or static stretching is still unclear, and probably involves both neurophysiological and mechanical factors (Fryer, 2006). AKE provides a reliable measure of range of motion, but does not measure the torque generated to produce the stretch and does not give any evidence of a biomechanical change to the muscle property. The few studies that have measured torque applied in pre- and post-passive knee extension (PKE) following isometric stretching strongly suggest that a change in tolerance to stretch, rather than viscoelastic change, is the main mechanism for increased extensibility (Magnusson et al., 1996b; Ballantyne et al., 2003). It would be interesting to examine the effect of a longer term of treatment using torque-controlled PKE in order to determine if changes to the viscoelastic property of the muscle was affected over a longer time course. It should be noted that while the subjects in the present study displayed limited hamstring flexibility, all were asymptomatic and likely to be younger than a typical patient population. This is an important limitation of the study, because it is possible that differences in the efficacy of the two MET approaches may be found when treating a more representative patient population, such as an older group, those with hamstring pain or healing hamstring tears. It is feasible that these techniques may help to prevent adhesion and cross-link
ARTICLE IN PRESS A comparison of two muscle energy techniques for increasing flexibility formation in the repairing muscle (Lederman, 2005), and future study of these populations with these stretching approaches may yield information concerning relative treatment effectiveness that proves valuable for clinicians. Although the present study investigated MET without comparison to either a control or static stretching group, other researchers have reported significant differences between contract–relax treatments and passive stretching (Tanigawa, 1992; Wallin et al., 1985; Moore and Hutton, 1980). While there were significant differences between pre-initial and post final AKE measurements, a comparison to both a control and static stretching would have added greater validity to the results, and clearly demonstrated that both these post-isometric techniques were superior to passive stretching in this group of subjects. The present study demonstrated that both the Greenman and Chaitow approaches to MET resulted in increased AKE, both immediately following the treatments and 1 week after treatment. Further study relating to the relative efficacy of the specific components of MET techniques will be required to determine most appropriate clinical application.
Conclusion This study found that both Greenman and Chaitow muscle energy approaches produced increased AKE immediately after intervention, and demonstrated a carryover effect 1 week later. There was a significant increase in range of motion of the knee immediately following both treatments at both weeks, and a significant increase at the pretreatment measurement at Week 2. There was, however, no significant difference between the two applications. This suggests that variations in the elements of the techniques, such as the duration of passive stretch, may not have a significant influence on the efficacy of the technique for increasing hamstring extensibility.
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