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Research Paper 2010
Title: A comparative study of the effects of muscle energy technique and inhibition, directed at iliopsoas muscle, on hip extension.
Author: Lisa Opie BSc (Hons)
Supervisor: Alison Durant BSc (Hons) Ost
The British School of Osteopathy
275, Borough High Street, London SE1
Many thanks go to the BSO research team and in particular Melanie Wright for her patience. A special thank you goes to my supervisor Alison Durant for her support and guidance, to Katie Clare who assisted with the data collection and my fellow BSO students who volunteered to be participants in this study.
Objective: The purpose of this study was to compare the effectiveness of
two osteopathic techniques, muscle energy (MET) and inhibition, directed at the iliopsoas muscle (IP), on hip extension.
Design: This study was a randomised, controlled, pre-post test experiment intervention with 3 independent variables, MET, inhibition and control. The dependent variable was the number of degrees by which hip extension increased.
Methods: 60 asymptomatic volunteers, all BSO undergraduate students, participated in this study. Participants were randomly placed into 3 groups: G1 received MET and G2 received inhibition, to the iliopsoas muscle of their dominant side, G3 (control) received no intervention. Data was recorded, pre- and post-intervention, on degrees of hip extension, using the modified Thomas test. Statistical analysis using paired t-tests (p=<0.05) were applied to compare mean gains in degrees of hip extension, between the groups.
Results: Paired t-tests showed a statistical difference in the change in degrees of hip extension for MET but not for inhibition or control, which implies that MET has produced significantly greater gains in range of motion compared to inhibition and control. No significant difference in degrees of hip extension was shown between inhibition and control groups.
Conclusion: In this group of asymptomatic participants, results demonstrate the immediate success of MET (isometric contraction followed by a passive stretch) in increasing hip extension, when applied to the iliopsoas muscle. No significant change was shown in the inhibition or control groups.
Hip flexor extensibility
Modified Thomas test
Muscle energy technique
Myo-fascial trigger points
A common cause of reduced hip extension is shortening of the iliopsoas (IP) muscle (Hammer 93). Furthermore there appears to be a causal relationship between reduced hip flexor muscle extensibility and low back pain (LBP) (Reuben & Inger 1989, Hammer 1995), with Godges et al (1993) advocating that limited hip extension leads to excessive, compensatory, lumbar spine extension. It is widely agreed that the IP muscle is the primary and most powerful hip flexor and the only muscle that acts on both the hip joint and the vertebral column, both as a flexor and stabiliser (Crosby et al 1998, Eland 2001, Kapandji 1987). Chiropractor Hammer (1995) agrees that due to its major function, the IP muscle is commonly overused or injured; he reports that 8-15% of his patients with IP dysfunction have related LBP. This makes the IP an important complex to assess and consequently treat; the aim to improve its extensibility and thus restore normal function (Yoshio et al 2002).
Clinically, osteopaths and other manual therapists have used many treatments to release tension and increase the range of motion of shortened or hypertonic tissues: ischemic compression (Aguilera et al 2009, Fryer & Hodgson 2005), muscle energy techniques (MET) (Chaitow 2006, Smith & Fryer 2008), neuromuscular techniques (Chaitow 2003), strain-counterstrain (Ibanez-Garcia et al 2009, Jones 1981), needling therapies (Reuben & Ingber 1989), trigger point release (Ferdandez-de-las-Penas 2006) and others. However a lack of published research makes it difficult for osteopaths to decide on the most effective method to employ (Smith & Fryer 2008).
Muscle Energy Technique
MET, which is also referred to as contract-relax (CR) or proprioceptive neuromuscular facilitation (PNF) (Fryer & Ruszkowski 2004), involves an isometric contraction (IC) of the agonist or antagonist muscle, against the practitioner’s counter resistance, in order to achieve optimum relaxation of the muscle to be stretched (Rowlands et al 2003). Osteopaths Smith and Fryer (2008) and Rowlands et al (2003) all claim that MET results in greater changes in ROM and muscle extensibility than other stretching technique. Lederman (2007) describes MET as a non-specific treatment but attributes its success to its target of and effect on multiple joint structures.
The osteopathic literature proposes various applications of MET including variations in length of IC, length of passive stretch, number of repetitions and even the percentage effort required for the IC. Controversy over the optimum length of the IC exists, with times ranging from 3s to 20s (Rowlands et al 2003). Rowlands et al (2003) set out to compare the effects of a 5s and 10s IC on hamstring flexibility and found that the longer contraction time led to greater gains in flexibility. However, their study was on chronic gains in flexibility and over a 6 week period; they suggest that for acute gains a shorter IC is sufficient. After a comprehensive review on the topic, Chaitow (2006) suggests that an IC of 7-10s is required in order to sufficiently influence muscle inhibition. Smith & Fryer (2008) used 7-10s IC, to increase hamstring flexibility and asked for 40% of maximum effort during the IC phase, this is in contrast to Chaitow (2006) who recommends 15-25% of maximum when treating psoas major and Handel et al (1997) who used a maximum IC in athletes. It is possible that athletes are more able to repeatedly sustain a maximum IC; however, it is likely that the general population and particularly symptomatic patients would not be able to achieve maximum effort.
Most of these studies have been carried out on the hamstrings, but two studies by Fryer and Ruszkowski (2004) and Schenk et al (1994) investigated IC duration on the atlanto-axial (AA) joint rotation. They agreed that a 5s IC produced significant changes when compared to 20s and a control group, which only produced moderate changes. Suggestions are made by Fryer & Ruszkowski (2004) that hamstring MET requires a more vigorous stretch or greater contraction force compared to light forces applied in spinal MET and therefore benefit from the longer IC time. Given the limitation of a small sample size (n=18 per group), in Fryer and Ruszkowski’s (2004) study, their results may not have had the power to generalise the findings to a larger population.
Post IC stretch time is also a topic of debate in most papers on MET. Smith & Fryer (2008) compared a 2-3s to a 30s post IC stretch time, in their study on the hamstring muscle group and found that both variations were equally as effective in increasing hamstring extensibility. In most of the studies mentioned, the participants have been young (early-mid 20s) and asymptomatic; the results may have proven different if the subjects had been older or had acute or chronic shortening. It has been recommended that for chronic shortening a vigorous 10s stretch should be preceded by a 10s IC in order to recruit the maximum number of motor units (Hammer 1995). In one study Feland et al (2001) used participants over the age of 65 and found that a 60s passive stretch was required to increase hamstring length in these patients.
Ischemic compression or inhibition (term used in this study) is a technique used to release or normalise hyper-tension in tissues (Cash 1996, Chaitow 2006). Chaitow (2003) describes this technique, as a steady constant pressure applied to soft tissues using fingers, thumb or elbow at a mild-moderate amount of force with the aim of decreasing tonicity. DiGiovanna et al (2005), equates its application to acupressure, a steady pressure to soft tissues in an attempt to normalise reflex activity within the tissue and thus have a lengthening effect on the muscle.
Despite inhibition being one of the oldest methods of manual treatment, there is very little published research into its mechanism. The majority of studies, into this neuromuscular technique, are carried out on the effects of inhibition on myo-fascial trigger points (MTrPs) (Aguilera et al 2009, Fernandez-de-las-Penas 2006, Ibanez-Garcia et al 2009, Hammer 1997). In treating the IP muscle Hammer (1997) claims that the application of a strong direct pressure into a number of trigger points is often more effective than a high velocity thrust (HVT), he warns that this technique can be extremely painful to the patient but to great effect. Smith and Mehta (2008) compared high velocity thrusts with sub-occipital inhibition on the upper cervical region and the effect on standing balance. They reported that both techniques were successful but thought that the soft tissue option carried less contra-indication. This study, however, was limited by the low number of subjects (10 per group) who were also young (mean age of 26.1) and asymptomatic. These restrictions make it difficult for the researchers to generalise their findings.
Much conflict exists amongst practitioners regarding the clinical application of inhibition, including the optimum amount of pressure and the length of hold, let alone the therapeutic mechanisms behind the technique. Chaitow (2006) believes that the most important component of inhibition is to apply a low-level, constant pressure to the dysfunctional tissue, to gain an effective release.
A number of studies have used pain threshold meters to monitor the consistency of the applied digital pressure (Fryer & Hodgson 2005, Fernandez-de-las Penas et al 2006). Finley & Cime (2008) recommend that in order to minimise any pain felt by the patient and to standardise pressure when applying such a myo-fascial release technique, a pressure threshold meter could be used. Others have used a pain scale where patients report on when pressure reaches a certain threshold. Simons (2002) recommends applying pressure that causes moderate pain and equates it to 7/10 on the scale, the practitioner maintains this until the pain reduces to a lesser value (3 or 4), which according to the researchers, occurs after approximately 20-30s. There are suggestions that some of the reduction in tenderness may be due to the practitioner unintentionally releasing pressure, which Fryer & Hodgson (2005) discovered in their study. However Gilbert (2009) concluded that osteopaths, whilst carrying out sub-occipital inhibition, were consistent in replicating their own digital pressure on different occasions, showing strong intra-rater reliability, compared to significant variations between practitioners.
Variations in the duration of digital compression for inhibition also exist amongst researchers and practitioners. DiGiovanna et al (2005) recommends holding pressure for 20 -60s. Hou et al (2002) compared 30, 60, and 90s on the trapezius muscle, using two pressure loadings and found that most combinations produced significant changes and claimed that only 30s of inhibition was required to obtain pain relief in MTrPs. Fryer & Hodgson (2005) used 60s sustained pressure on MTrPs in the upper fibres of trapezius (UFT) and reported immediate decreases in sensitivity, compared with no significant changes with a sham technique. Although the presence of MTrPs in the UFT was an inclusion criterion, the patients in this study, were asymptomatic and therefore may not be typical of the population seeking treatment.
Research Aims and Questions
The aim of this study was to compare the effectiveness of two osteopathic techniques, MET and inhibition, applied to the iliopsoas muscle, on hip extension.
.Hypothesis 1: MET and inhibition carried out on IP, will be more effective in increasing hip extension, than the control.
Hypothesis 2: There will be a difference between the effects of MET and inhibition carried out on IP, on increasing hip extension.
Sixty asymptomatic, participants (mean age= 28.7, M:F 23:37) were recruited from the student population at the British School of Osteopathy (BSO) London through the college intranet, via email invitation which included an information Sheet (PIS). Participants were included on completing and passing the medical screening questionnaire and signing a consent form. Volunteers under the age of 18 or over 45 were excluded, as were those who were considered symptomatic due to a positive response to any of the medical screening questions.
Participants were randomly assigned to Group 1 MET, Group 2 Inhibition and Group 3 Control. Sample size was determined by the BSO guidelines for undergraduate projects. (See appendix 1 for sample PIS & screening sheets).
Ethical approval for this study was granted by the British School of Osteopathy Research Ethics Committee (BSOREC).
This study was a randomised, controlled, pre-post test experiment intervention with 3 independent variables, MET, inhibition and control. The dependent variable was the number of degrees by which hip extension increased.
A pilot study was conducted on 10 participants, prior to the main study, for two main reasons:
1. to highlight any potential difficulties in the methodology
2. to select the most appropriate/effective treatment intervention times for MET and inhibition.
It became evident in the pilot study that using the sidelying position for the inhibition technique was not going to produce reliable results. The technique was too tiring for the researcher to maintain a consistant digital pressure on the iliopsoas muscle. This was discussed with the supervisor and research team at the BSO and agreed that the supine position would be easier to administer and just as effective as the sidelying position.
Relevant changes/modifications were then implemented for the main study, thus increasing its reliability.
Hip extensibility, of the dominant limb, was measured using the modified Thomas test (MTT). The reason for using the MTT was that it is widely thought to be a reliable and easily administered test (Godges et al 1993, Kendal et al 1993, Winters et al 2004) with intraclass correlation coefficients for interrater and intrarater reliability of .98 (Winters et al 2004). Measurements in degrees of hip extension were taken using a universal goniometer, one pre and one post intervention (See Figure 1 & appendix 2 for details on MTT).
Figure 1. Goniometric measurement of hip extensibility
using the modified Thomas test
The MET group were instructed to produce a 10s isometric contraction into hip flexion, followed by a passive stretch of 20s, on their dominant leg. This was repeated twice in a side lying position (figure 2, appendix 2).
The inhibition group received a slow controlled, mild to moderate digital pressure for 30s to the iliopsoas muscle. This was also repeated twice in the supine position (figure 3, appendix 2).
The control group received no intervention and rested for 2 minutes between
Figure 2. Muscle energy technique Figure 3. Inhibition
On fulfilling the inclusion criteria and signing the consent form, each participant was randomly assigned to one of the three groups by selecting from a hat, number 1 for MET, number 2 for Inhibition, or number 3 for control group. Participants were offered a chaperone and advised prior to the study that they would be required to dress down to a pair of shorts, which were provided.
A line was drawn from the greater trochanter to the femoral condyle on each participant’s dominant limb. Researcher 1 (undergraduate osteopathic student) who was blinded to the group allocation, used a goniometer to measure degrees of hip extension, of the dominant leg and then left the room.
Researcher 2 (BSc (Hons) sport rehabilitation/sport science & final year osteopathic student) blinded to pre-intervention measurement then entered the room and according to group allocation treated the hip of the experimental leg with: MET (n=21), inhibition (n=19) for groups 1 & 2 respectively and control group 3 (n=20) received no intervention and rested on the table for 2 minutes. Researcher 2 then left the room and researcher 1 returned to take the post–intervention, final measurement.
Analysis of data
All data was collated and analysed using SPSS version 17. Pre and post intervention measurements, in degrees, were analysed for the three groups. The independent variables were MET, inhibition and control. The dependent variable was the number of degrees by which hip extension increased. Paired t-tests were applied to compare mean gains in ROM (post intervention) between the groups. A p value of <0.05 was considered statistically significant. Further tests for potential confounding variables (ie. age and gender) were also carried out.
a there was no significant difference (p>0.05) between the groups using a chi-square tests
b there was no significant difference (p>0.05) between the groups using Mann Whitney U tests
Table 1 shows the demographic data for the participants by group (p>0.05). Age was found to be statistically skewed (Shapiro-Wilk = 0.922, p=0.001) and therefore median values have been presented.
Group Measure Nos Mean S.D. Independent
Group Measure Nos Mean S.D. Independent
As both pre- and post- intervention measurements were normally distributed, parametric t- tests were used to compare the groups (Shapiro-Wilk = pre 0.985, post 0.989, p= pre 0.653, post 0.868).
Paired samples tests are shown in tables 2 &3. Analysis shows that there was a statistical difference between the groups in both the pre-intervention measurements and the change (post-intervention). The base-line measurement for inhibition was significantly higher than for MET but the overall gains in degrees of hip extension were significantly higher for the MET group. A statistical difference in the change in degrees of hip extension is shown for MET but not for inhibition or control, which implies that MET has displayed significantly greater gains in degrees of hip extension compared to inhibition and control. No significant difference in change of degrees of hip extension was shown between inhibition and control.
This current study aimed to test whether MET and inhibition directed at the IP muscle, was more effective than the control group in increasing hip extension and to identify if one technique was more effective than the other. Participants were asymptomatic and only immediate effects were measured. Data analysis revealed that MET was significantly more effective than both control and inhibition. No significant difference was found between inhibition and control groups.
It was somewhat surprising that the inhibition group made no significant improvements in hip extension in this current study, as it is a technique frequently used by osteopaths and other manual therapists either in isolation or in conjunction with other techniques in order to do so, via a supposed lengthening effect on the IP (Fernandez-de-las-Penas et al 2006, Aguilera et al 2009). Variables that may have influenced the outcomes and therefore validity of this study need to be considered.
The base-line measures for group 2 (inhibition) were higher than the other groups, in particular MET. Participants were randomly assigned to groups and the respective researchers were blinded to pre-intervention measurements and group assignment, assuring no bias. It is possible that participants in this group participate in regular stretching activities ie. yoga, dance or martial arts. Had this data been included it may have explained the greater base-line measurements in group 1, a consideration for future studies.
With the exception of Smith & Mehta’s (2008) study, who applied soft tissue inhibition to the sub-occipital muscles, most research into the effects of inhibition have been carried out on MTrPs or dysfunctional tissue (Aguilera et al 2009, Chaitow 2003, Fernandez-de-las-Penas et al 2006, Fryer & Hodgson 2005, Ibanez-Garcia et al 2009). A concern in Fryer and Hodgson’s (2008) study was that the application of sustained pressure on latent MTrPs would irritate and increase their sensitivity; this was not found to be the case and instead a reduction in perceived pain was reported. This is supported by a chiropractor (Rich, 1997) who claims that trigger-point therapy into an iliopsoas muscle in spasm is extremely painful but successful. This may suggest that the effects of inhibition may be greater when applied to dysfunctional tissue.
In applying the optimum length of time and pressure for inhibition literature recommends two approaches: that pressure is sustained until the clinician feels a release of the underlying tissues or the use of a pain scale, where patients report when pain reduces to a certain value (Fryer & Hodgson 2008). The pain scale was used in this study with two applications of 30s of inhibition, to ensure a consistent pressure. The intervention may have been effective had the researcher combined their objective palpable, release of the tissue with the participant’s subjective feedback and allowed up to 90s for tissue change, a time frequently recommended allowing for tissue release (Fernandez-de-las-Penas et al 2006).
MET, in this study, showed to be effective in increasing hip extension, findings that are consistent with reports on the effectiveness of MET on the hamstring muscles (Rowlands et al 2003, Smith & Fryer 2008) and the piriformis (Wright & Drysdale 2008). No studies were available on the effects of MET on the iliopsoas.
It is possible that due to its effect on multi-joint structures such as muscles, ligaments and fascia (Lederman 2007), MET was the more successful technique in this study. This is supported by Morgan (1989) who claims that somatic dysfunction in any one of the myo-fascial structures associated with iliacus will be effected by MET by invariably providing an effective, non-specific treatment.
Crosby et al (1998) refers to the psoas major, minor (if present) and iliacus collectively as the ‘iliopsoas compartment’ and describes it as being enclosed within a thick and tight fascial envelope. Perhaps the success of the more non-specific treatment in this study could be attributed to the fact that due to its location and surrounding fascial attachments the ‘iliopsoas compartment’ is difficult to palpate directly.
This study had several limitations. The participants were all asymptomatic and did not necessarily display limited hip extension and therefore may not represent the typical population presenting to an osteopath for treatment. Had the participants been more representative of the population, the outcomes may have been different. Only the immediate effects of a single treatment of MET and inhibition were examined with no follow up and therefore the duration of the effects of the interventions are unknown.
It is recommended that future studies include symptomatic or even asymptomatic patients who present with limited hip flexor muscle extensibility. Further studies on the effects of inhibition on latent or active MTrPs within the iliopsoas muscle, over a longer treatment and assessment period, would investigate the long term effects. An initial pilot study, determining the most effective protocol for the application of sustained manual pressure to the iliopsoas muscle, would also be highly recommended. Further experimental studies into the effects of inhibition or sustained manual pressure would benefit from the use of a pressure feedback monitor which was used in previous studies by Fryer & Hodgson (2009) and Fernandez- de- las- Penas et al (2006) to ensure practitioner consistency.
The results show that in the short term, MET (isometric contraction followed by a passive stretch) applied to the IP muscle, is successful in increasing hip extension. No significant change was shown in the inhibition or control groups. Variations in the application of inhibition, such as the duration, amount of pressure applied, presence of MTrPs and symptomatic versus asymptomatic, may show significantly contrasting results and warrants further investigation.
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