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Muscle timing and activation patterns during two movement screening tests in subjects with and without low back pain.

Introduction

Low back pain (LBP) is one of the most common conditions experienced by the majority of society. In the United States, LBP is one of the top five reasons for physician office visits with approximately 19 million visits reported in 2001 (Deyo, Mirza, & Martin, 2006; Panel on Musculoskeletal Disorders and the Workplace, 2001). Lifetime prevalence has been reported to be between 60% and 90% (Anderson, 1991; Waddell, 1987) and at any given time 6.8% of the world's population is affected by LBP (Cox, 2011). According to Patel and Ogle (2000), 50% of the active work force will experience symptoms related to LBP annually. It is one of the principal causes of absenteeism from work and daily activity impairment (van Dieen, Selen, & Cholewicki, 2003). One in five individuals with LBP report substantial limitations in activity (Von Korff & Saunders, 1996). After an acute episode, approximately 33% will report persistent back pain of at least moderate intensity during the following year (Von Korff & Saunders, 1996). Further, 10% of all patients suffering from LBP will experience disability lasting greater than three months (Woby, Watson, Roach, & Urmston, 2004).

Individuals with back pain were found to have trunk extensor weakness, excessive fatigability and poor lumbar muscle endurance (Pitcher, Behm, & MacKinnon, 2008; Taimela, Kankaanpaa, & Airaksinen, 1998). Low back pain has also been shown to negatively affect maximum voluntary muscle activation, through neuromuscular inhibition and/or altered motor control patterns of the trunk (O'Sullivan, Phyty, Twomey, & Allison, 1997; Richardson & Jull, 1995; Zedka, Prochazka, Knight, Gillard, & Gauthier, 1999).

In order to identify appropriate strengthening exercises, many studies have focused on muscle activity levels as opposed to understanding the muscle firing sequence and how it may differ in individuals with back pain. Electromyography (EMG) studies of the trunk musculature found that individuals with LBP displayed differences in muscle group amplitudes/activation levels that could not be explained by postural asymmetries (Dolce & Raczynski, 1985; Lariviere, Gagnon, & Loisel, 2000). Bullock-Saxton, Janda, and Bullock (1994) found that subjects with LBP experienced a delay in gluteus maximus firing while prone and gluteus medius firing while sidelying. Irregular firing patterns may lead to compensatory substitutions which reduce the effectiveness of stabilizing muscles (Danneels et al., 2002). Subjects with LBP also produced significantly lower force values (during isometric contraction) in the lumbar iliocostalis and the longissimus than those without pain (Candotti et al., 2008).

The prone straight leg raise (PSLR) and sidelying hip abduction (SHA) movement tests are frequently used to screen patients with low back and/or pelvic dysfunction (Davis, Bridge, Miller, & Nelson-Wong, 2011). Individuals with these dysfunctions seem to display altered movement patterns, making this type of screen appropriate. SHA may be useful in predicting low back pain (LBP) development during prolonged standing tasks (Nelson-Wong, Flynn, & Callaghan, 2009). It is important to understand normal firing patterns in order to correctly identify muscle dysfunction and choose effective treatment interventions (Vogt & Banzer, 1997). Therefore, the purpose of this study was to examine if differences exist in hip and trunk muscle activation and firing patterns during 2 movement screening tests in individuals with low LBP and healthy controls. Based on previous literature, we hypothesized that back muscle onset times and muscles firing patterns would differ between those with and without LBP.

Methods

Subjects

Twenty-two healthy active subjects serving as a control group (11 males, 11 females; mean [+ or -] SD age, 27.2 [+ or -] 4.6 years; body mass index, 24.7 [+ or -] 4.9 kg/[m.sup.2]) and 12 subjects with LBP (5 males, 7 females; mean [+ or -] SD age, 44.4 [+ or -] 14.6 years; body mass index, 29.7 [+ or -] 10.3 kg/[m.sup.2]) volunteered to participate in this study. All subjects were 18 years of age or older and completed an informed consent form that described the testing protocol, which was approved by the University of Maryland Eastern Shore Institutional Review Board for protection of human subjects. Female subjects were excluded if they were currently pregnant or gave birth within the last 2 years.

The control group was recreationally active and participated in physical activity for an average of 3.5 hours per week. Subjects were in good general health and reported no symptoms of injury at the time of testing, no back or lower extremity pain for the past 6 months, and no history of back or lower extremity surgery. Subjects with low back pain were recruited from local physical therapy clinics and accepted for the study if they (1) reported that the back pain began within the last two months; (2) described a current level of pain 3 on a (0 to 10) visual analog scale; and (3) were referred to physical therapy by a physician or self-referred. Subjects with LBP were excluded if any of the following were present: (1) a history of back or lower extremity surgery; (2) signs of nerve root compression (2 or more of the following: positive straight leg raise test at an angle less than 45[degrees] or diminished lower extremity strength, sensory function, or deep tendon reflexes); and (3) evidence of serious pathology (e.g., acute spinal fracture, tumor, infection, etc).

General Practice Physical Activity Questionnaire (GPPAQ)

The GPPAQ provides a simple, four-level Physical Activity Index (PAI) reflecting an individual's current physical activity level. The instrument is intended for adults (16-74 years of age) and is a simple tool, requiring 30 seconds to complete. The GPPAQ has been shown to have good face and construct validity (Khaw et al., 2006). Subjects in the control group were asked to complete the GPPAQ in order to better understand their physical activity level in terms of their job and the type and amount of aerobic exercise regularly performed.

Pain Intensity

The visual analog scale (VAS) has been shown to be a valid and reliable instrument used to measure intensity of pain (McCormack, Horne, & Sheather, 1988; Price, McGrath, Rafii, & Buckingham, 1983). A 10-cm visual scale, with written descriptors at 0 ("no pain") and 10 ("maximum pain"), was used to understand pain intensity and determine participation eligibility. Subjects with LBP were asked to rate their current pain intensity and describe the current pain location.

Protocol

Subjects attended one test session. During this time demographic data was collected, questionnaires completed, and subjects were assessed for the movement tests under investigation. Testing was performed on the dominant lower extremity or, in subjects with LBP, the pain dominant or movement impaired lower extremity. The EMG procedure consisted of electrode placement, practice and familiarization, and muscle onset timing assessment.

Electrode Placement

Subjects were prepared for electrode placement. Alcohol was used to cleanse the skin and reduce tissue impedance. Bipolar surface electrodes (Noraxon USA, Inc; Scottsdale, AZ) were placed on the selected muscles for each test, according to a basic understanding of surface anatomy (Greenman, 2003; Kendall, 2005). All of the posterior trunk and hip/thigh muscles (primarily responsible for the movement under consideration) accessible for assessment with surface EMG (Konrad, 2006) were investigated. Electrodes were silver-silver chloride pre-gelled with a diameter of 1 cm and inter-electrode distance of 2 cm. The same examiner, a physical therapist with approximately 14 years of clinical experience and a board certified orthopedic clinical specialist, positioned the electrodes on all subjects. Each electrode was connected to a Noraxon Telemyo 2400T G2 transmitter (Noraxon USA, Inc; Scottsdale, AZ). The sampling rate was 1500 Hz. All raw myoelectric signals were pre-amplified (overall gain, 500). The common mode rejection ratio was >100 dB, the signal-to-noise ratio was <1 [micro]V RMS baseline noise, and filtered to produce a bandwidth of 10-500 Hz.

For both movement tests, the same trunk muscles (lumbar multifidus and lumbar erector spinae) were recorded on both sides of the torso. The lumbar multifidus electrodes were placed 2 cm lateral to the L5 spinous process. Lumbar erector spinae electrodes were placed 4 cm lateral to the L3 spinous process. The lower extremity muscles differed for each movement test. During the PSLR, the Gluteus Maximus electrodes were placed 4 cm inferior to the posterior superior iliac spine. The medial and lateral hamstring electrodes were placed at the mid-thigh level, between the gluteal fold and the respective femoral condyle. During SHA, the tensor fascia latae electrodes were placed at the mid-point of an imaginary line between the greater trochanter and the anterior superior iliac spine (ASIS). The Gluteus Medius electrodes were applied 2.5 cm posterior to the midpoint of the line bisecting the ASIS and greater trochanter.

All electrodes were aligned parallel to the fiber direction of the target muscle. Correct electrode placement was verified by EMG signal analysis (visual inspection) during the motion test under consideration. This information was also used to ensure that a true baseline was maintained at rest. A reference electrode was placed along the shaft of the most palpable rib posteriorly, on the right mid-axillary line.

Movement Tests

All subjects were screened to ensure they were able to perform each movement test. The test leg was identified and each subject was familiarized with the desired movement (verbally and visually) and practiced the motion twice. Corrective feedback was provided, if needed. With EMG equipment, each subject performed 2 trials for reliability and 2 trials for timing analysis, for each movement test. A standardized set of computer generated voice commands were used to synchronize the data collection process. Upon command, subjects moved into the desired position and held that position for 3 seconds. Subjects rested for 1 minute between trials.

The prone straight leg raise was the first movement test analyzed. Subjects were positioned their stomachs with their knees extended and ankles off the edge of the table. From this position, maximal hip extension was performed (Figure 1A). The next movement test analyzed was sidelying hip abduction. For this movement test, subjects were positioned on his or her non-test side with the test leg in neutral, resting on a pillow, with the knee extended. From this position, maximal hip abduction was performed (Figure 1B).

Data Processing

Raw EMG data were converted from analog to digital at 1500 Hz. The raw signals were rectified, smoothed, and reduced for cardiac artifact. Activation of the different muscles was determined for each movement test. We analyzed a 5 second window starting from the point where the subject was given the verbal command to contract. A muscle was considered to be activated when the signal surpassed the trigger level of 3 standard deviations beyond the baseline activity level at the beginning of the concentric phase of the motion. This method sets activation at a higher threshold and is considered to be a reliable technique (Bolgla, Malone, Umberger, & Uhl, 2010; Di Fabio, 1987). The point in time when each muscle reached this activity level was determined. If a muscle did not reach this level, the onset time was coded as 5 seconds. These measures of time were averaged for each muscle during both movement tests.

Statistical Analysis

The statistical analysis was performed using Statistical Package for the Social Sciences, version 19.0 (SPSS Inc, Chicago, IL). An intraclass correlation coefficient (ICC) was used to determine same day test-retest reliability of the EMG recordings. The individual mean muscle onset times were averaged, across the group, to determine overall mean onset time for each muscle. From this data, the firing patterns for the 2 movement tests (PSLR and SHA) were established. A 1-way analysis of variance (ANOVA), with age as a covariate, was applied for each muscle to identify differences between groups. This was performed for each movement test.

Results

Prone Hip Extension

During prone hip extension, Vogt and Banzer (1997) showed that in asymptomatic individuals, the ipsilateral erector spinae was recruited prior to the hamstrings. During the same motion, the gluteus maximus was the last muscle, within the muscles assessed, to be activated (Lehman, Lennon, Tresidder, Rayfield, & Poschar, 2004; Sakamoto et al., 2009; Vogt & Banzer, 1997). Results from our study revealed a similar activation pattern for subjects without LBP. The gross recruitment pattern began with the contralateral trunk extensors, followed by the ipsilateral trunk extensors, and finally the gluteus maximus. The immediate activation of the contralateral trunk muscles may initiate a stabilization process and balance the force required to move the limb on the opposite side of the body.

We found that this pattern was generally reversed in subjects with LBP as the recruitment process moved from a distal to proximal direction, with the exception of the gluteus maximus. In both groups, the gluteus maximus was the last muscle to fire. However, when comparing gluteus maximus activation times between groups, the onset time was significantly longer in subjects with LBP. This delay in activation of the gluteus maximus may have occurred secondary to inhibition of the stabilizing trunk musculature. Danneels et al. (2002) discussed how pain, pain avoidance and deconditioning may contribute to a reduction in back muscle EMG activity levels in subjects with LBP.

Sidelying Hip Abduction

When asymptomatic individuals performed SHA, the gluteus medius and tensor fascia latae were clinically observed to become active prior to the ipsilateral erector spinae, with the GM firing first (Greenman, 2003). Our results for sidelying hip abduction showed that subjects with and without low back pain displayed a similar muscle firing pattern, recruiting the lower extremity prior to the low back musculature. However, subjects with low back pain displayed a significant delay in the onset times for all of the back musculature examined. Although not found to be statistically different, subjects with low back pain displayed a mean delay of gluteus medius activation by more than one second. This delay in gluteus medius activation, possibly due to inhibition of the back musculature, may be clinically significant and could lead to abnormal movement patterns. Previous research has identified gluteus medius weakness as a factor that contributes to lower extremity injury via altered joint loading patterns and reduced motor control (Fulkerson, 2002; Powers, 2003).

The sidelying hip abduction screening tool performed moderately well in predicting those who are at risk for developing low back pain during prolonged standing (Nelson-Wong et al., 2009). This motion has also been show to be effective in activating the gluteus medius (Bolgla & Uhl, 2005; Distefano, Blackburn, Marshall, & Padua, 2009; Ekstrom, Donatelli, & Carp, 2007).

The same day test-retest ICCs for the EMG recordings from each muscle during each movement test are provided in Tables 1 and 2. These data suggest moderate to high reliability across trials for all muscles during each movement test. The only exception identified was the ipsilateral erector spinae during the PSLR, which was less reliable.

During the PSLR movement test, subjects with LBP activated the extremity muscles earlier than the back musculature. In healthy subjects, this pattern was reversed. In both groups, the gluteus maximus was the last muscle to be recruited. During SHA, the recruitment patterns were similar for both groups (extremity muscles fired before trunk musculature).

Significant differences in muscle onset timing were identified during both the PSLR and SHA tests. Compared to controls, subjects with LBP displayed a significantly greater gluteus maximus (P=.001) and ipsilateral erector spinae (P=.037) activation times during the PSLR (Table 3). Subjects with LBP also demonstrated significantly greater trunk muscle activation times (Pd".002), for all trunk muscles, during SHA (Table 4).

Muscle onset timing data and recruitment sequence for the PSLR and SHA are summarized in Tables 3 and 4, respectively. Subjects with LBP described their current pain intensity (mean [+ or -] SD) as 4.1 [+ or -] 1 cm on the VAS. Forty-one percent of the subjects with LBP reported having current pain in the central low back, 25% described pain in the right low back and right posterior thigh, 17% had pain in the left low back, and 17% had pain in the left low back and left posterior thigh.

Discussion

The main objective in this study was to examine the differences in muscle onset timing and firing patterns during two frequently used screening tests in individuals with and without LBP. Significant differences in muscle onset times were identified between the two groups. During both movement tests, activation of the spine musculature was delayed in subjects with LBP. In addition, during the PSLR, subjects with LBP experienced a significant delay in gluteus maximus and ipsilateral erector spinae firing with a general reversal of muscle group recruitment patterns.

The movement tests examined in this study were chosen because they are commonly used by physical therapists to screen patients with low back and/or pelvic dysfunction. The quantity and quality of motion is assessed as well as any movement substitutions, secondary to abnormal muscle recruitment and/or symptom changes. Differences in muscle firing patterns have been linked to low back pain (LBP) and it has been suggested that clinicians should measure not only the strength, but also consider the sequence of trunk muscle activation (D'Orazio, 1993; Greenman, 2003).

When using the PSLR as a screening tool for individuals with low back pain, it is important to recognize that the gluteus maximus is expected to fire last and that palpation should be used to assess for muscular inhibition. Therapists should consider palpation of the lumbar musculature and gluteus maximus in order to identify gross side-to-side inhibition asymmetries while observing for any movement substitutions. When using SHA as a screening tool for individuals with low back pain, it is important to recognize that that the low back musculature (paraspinals and multifidii), on both sides of the trunk, may be dysfunctional. During this test, therapists should consider palpating both sides of the trunk musculature while simultaneously observing for any abnormal movement patterns. In patients with LBP, abnormal firing patterns may lead to compensatory substitutions which reduce the ability of the stabilizing muscles to perform optimally (Danneels et al., 2002). Several authors agree that the most common pathologic substitution, during the SHA, seems to be a delay in activation of the gluteus medius (Bruno & J., 2007; Bullock-Saxton et al.,1994; Greenman, 2003). Hodges and Richardson (1998) concur and demonstrated that in patients with LBP, the normal proximal to distal muscle activation pattern was reversed.

Conclusion

The prone straight leg raise and sidelying hip abduction screening tools are frequently used by physical therapists to assess for abnormal movement patterns and/or muscle inhibition. Compared to controls, subjects with low back pain showed a general recruitment pattern of extremity prior to trunk musculature during the PSLR. In addition, subjects with low back pain showed a significant delay in activation of the gluteus maximus and the ipsilateral paraspinal muscles. During the second test, SHA recruitment patterns were nearly identical for both groups as the lower extremity muscles were activated before the trunk. However, compared to controls, subjects with low back pain showed a significant delay in activation of all trunk musculature. Therefore, back muscle inhibition should be an immediate treatment consideration for individuals who are experiencing low back pain and test positive on either of the movement screening tests. Additional research is warranted in identifying treatment interventions that are most effective in restoring normal firing patters and muscle activation in individuals with low back pain.

Acknowledgement

The authors would like to thank Dr. Frank Rosenthal with McCready Foundation Inc., Dr. Lamont Thompson with Shore Health Systems, and Dr. Ray Moore III with Physical Therapy First for their assistance in data collection.

References

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Michael Rabel

Department of Physical Therapy

University of Maryland Eastern Shore

Mike Lominac, PT, DPT

Department of Physical Therapy

University of Maryland Eastern Shore

Ryan Chase, PT, DPT

Department of Physical Therapy

University of Maryland Eastern Shore

Chin Yoon, PT, DPT

Department of Physical Therapy

University of Maryland Eastern Shore

TABLE 1
Within Subject Reliability For Each Muscle During
The Prone Straight Leg Raise

Muscle                          ICC    SEM
                                       (ms)

Contralateral Erector Spinae    0.90   293
Contralateral Multifidus        0.76   439
Ipsilateral Biceps Femoris      0.65   132
Ipsilateral Semitendinosus      0.65   180
Ipsilateral Multifidus          0.97   137
Ipsilateral Erector Spinae      0.39   899
Gluteus Maximus                 0.96   295

Abbreviations: ICC, intraclass correlation
coefficient; SEM, standard error of measurement;
ms, milliseconds.

TABLE 2
Within Subject Reliability For Each Muscle During
Side Lying Hip Abduction

Muscle                          ICC    SEM
                                       (ms)

Tensor Fascia Latae             0.77   439
Gluteus Medius                  0.90   365
Ipsilateral Multifidus          0.93   501
Ipsilateral Erector Spinae      0.98   276
Contralateral Erector Spinae    0.94   493
Contralateral Multifidus        0.96   401

Abbreviations: ICC, intraclass correlation
coefficient; SEM, standard error of measurement;
ms, milliseconds.

TABLE 3
Timing of Selected Muscles During The Prone Straight
Leg Raise *

Muscle           Control (n=22)
Under            Sequence &
Investigation    Mean Onset Time

Contralateral    1     720 [+ or -] 235
Erector
Spinae

Contralateral    2     738 [+ or -] 171
Multifidus

Ipsilateral      3     744 [+ or -] 173
Biceps
Femoris

Ipsilateral      4     747 [+ or -] 262
Semitendinosus

Ipsilateral      5     736 [+ or -] 227
Multifidus

Ipsilateral      6     823 [+ or -] 264
Erector
Spinae

Gluteus          7     882 [+ or -] 180
Maximus

Muscle           LBP (n=12)                 P
Under            Sequence &
Investigation    Mean Onset Time

Contralateral    5     1516 [+ or -] 1353   0.2
Erector
Spinae

Contralateral    4     1504 [+ or -] 1236   0.7
Multifidus

Ipsilateral      1     756 [+ or -] 243     0.7
Biceps
Femoris

Ipsilateral      2     824 [+ or -] 272     0.1
Semitendinosus

Ipsilateral      3     1363 [+ or -] 1207   0.3
Multifidus

Ipsilateral      6     2064 [+ or -] 1121   0
Erector
Spinae

Gluteus          7     2810 [+ or -] 1885   0
Maximus

* Values are expressed as mean [+ or -] SD milliseconds.

TABLE 4
Timing of Selected Muscles During Side Lying Hip Abduction *

Muscle Under      Control (n=22)
Investigation     Sequence &
                  Mean Onset Time

Tensor Fascia     1    648 [+ or -] 126
Latae

Gluteus Medius    2    648 [+ or -] 150

Ipsilateral       3    1086 [+ or -] 919
Multifidus

Ipsilateral       4    977 [+ or -] 404
Erector Spinae

Contralateral     5    2734 [+ or -] 1914
Erector Spinae

Contralateral     6    1546 [+ or -] 1463
Multifidus

Muscle Under      LBP (n=12)                P
Investigation     Sequence &
                  Mean Onset Time

Tensor Fascia     1    1282 [+ or -] 1333   0
Latae

Gluteus Medius    2    1629 [+ or -] 1715   0

Ipsilateral       3    4176 [+ or -] 1283   < .001
Multifidus

Ipsilateral       6    4887 [+ or -] 393    < .001
Erector Spinae

Contralateral     5    4814 [+ or -] 490    0
Erector Spinae

Contralateral     4    4431 [+ or -] 1295   < .001
Multifidus

* Values are expressed as mean [+ or -] SD milliseconds.
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Author:Rabel, Michael; Chase, Ryan; Lominac, Mike; Yoon, Chin
Publication:Journal of the National Society of Allied Health
Article Type:Report
Geographic Code:1USA
Date:Mar 22, 2013
Words:4948
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