Accepted Manuscript EMG activity and force during prone hip extension in individuals with lumbar segmental instability Hee-Seok Jung , Sun-Young Kang , Joo-Hee Park , Heon-Seock Cynn , Hye-Seon Jeon PII:

S1356-689X(14)00222-7

DOI:

10.1016/j.math.2014.11.002

Reference:

YMATH 1645

To appear in:

Manual Therapy

Received Date: 2 January 2014 Revised Date:

27 October 2014

Accepted Date: 4 November 2014

Please cite this article as: Jung H-S, Kang S-Y, Park J-H, Cynn H-S, Jeon H-S, EMG activity and force during prone hip extension in individuals with lumbar segmental instability, Manual Therapy (2014), doi: 10.1016/j.math.2014.11.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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EMG activity and force during prone hip extension in individuals with lumbar segmental instability Hee-Seok Junga, b, Sun-Young Kangb, Joo-Hee Parkb,

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Heon-Seock Cynnc, Hye-Seon Jeonc, *

Department of Physical Therapy, Seoul-chuk Hospital, Seoul, Republic of Korea

b

Department of Physical Therapy, The Graduate School, Yonsei University, 1 Yonseidae-gil,

Wonju, Kangwon-do 220-710, Republic of Korea

Department of Physical Therapy, College of Health Science, Yonsei University, 1

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c

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a

Yonseidae-gil, Wonju, Kangwon-do, Republic of Korea

This work should be attributed to the Department of Physical Therapy, Yonsei University

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Corresponding author: Hye-Seon Jeon, Department of Physical Therapy, Graduate School, Yonsei University, 1 Yonseidae-gil, Wonju, Republic of Korea. Tel.: +82-33-760-2498; fax: +82-33-760-2496.

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E-mail address: [email protected]. (H.-s. Jeon)

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EMG activity and force during prone hip extension in individuals with lumbar segmental instability

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Abstract:

The goal of the current study was to investigate potential differences in back and hip extensor muscle activity and hip extension force during prone hip extension (PHE) in individuals with lumbar segmental instability (LSI) and asymptomatic subjects. Thirty-six subjects with LSI and 26

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asymptomatic volunteers participated in this study. Muscle activity of the erector spinae, gluteus

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maximus, and biceps femoris was recorded using electromyography (EMG), and hip extension force was measured by a digital force gauge. Muscle activity was significantly greater in subjects with LSI than in asymptomatic subjects during PHE (p < 0.05). Hip extension force was significantly lower in the subjects with LSI than in asymptomatic subjects during PHE (p < 0.05). These findings suggest that during PHE, subjects with LSI have differences in back and hip extensor muscle activity and hip

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extension force compared to asymptomatic individuals.

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1. Introduction

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Keywords: Force. Lumbar segmental instability. Muscle activity. Prone hip extension

Lumbar segmental instability (LSI) is a potential source of low back pain (LBP) and is

believed to be associated with spinal dysfunction (O’Sullivan, 2000; Fritz et al., 2005). The estimated prevalence of LSI is reported to be 57% in patients with LBP and 12% in patients attending physical therapy for LSI (Alqarni et al., 2011). LSI is an encompassing term that includes mechanical (radiographic) and functional (clinical) instability (Panjabi, 2003; Beazell et al., 2010). Mechanical instability is considered related to excessive spinal segmental movement and is confirmed by radiography (Fritz et al., 2005; Beazell et al., 2010). Numerous studies have dealt with changes in segmental movement in relation with structural changes in the disc, which is a finding reported in

ACCEPTED MANUSCRIPT cases of disc degeneration (Mimura et al., 1994; Li et al., 2011; Ibarz et al., 2013). Panjabi (1992) defined a functional instability as loss of the spine’s ability to maintain intervertebral neutral zones under loaded conditions, resulting in pain and disability. According to theoretical modeling of the spinal stabilization system (Panjabi, 1992), spinal stability is achieved through a combination of the

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passive (structural) system, active (muscular) system, and the neural control system. Panjabi (1992) suggested that when the segmental stability of the passive system is compromised, the neuromuscular system might compensate to provide dynamic control to the lumbar spine. This compensation has

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been reported in patients with lumbopelvic instability (Hungerford et al., 2003; Tateuchi et al. 2013). Structures in the lumbopelvic region are often considered as shock absorbers transferring

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loads between the spine and lower limbs (Snijders et al., 1998; Hungerford et al., 2003). Numerous tests have been developed to evaluate the functional stability of the lumbopelvic region (Takasaki et al., 2009). Prone hip extension (PHE) is commonly used as a reliable self-perturbation task to test lumbopelvic stability (Murphy et al., 2006). Altered muscle activity between the back and hip extensors during PHE is one of the most commonly described dysfunctional patterns (Janda, 1996;

et al. 2013).

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Sahrmann, 2002) and may contribute to reduced lumbopelvic stability (Takasaki et al., 2009; Tateuchi

Recent studies have shown that coordinated back and hip extensor activity is critical to the

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stability of the lumbopelvic region during PHE (Arab et al., 2011; Tateuchi et al., 2013). Contractions of the gluteus maximus and hamstrings, which have connections to surrounding ligaments in the

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lumbopelvic region, produce hip extension force in a coordinated pattern (Snijders et al., 1993; Vleeming et al., 1995) and contribute to lumbopelvic stability during PHE (Chance-Larsen et al., 2010). Although individuals with LBP may have limited force generation in the hip extensors (Kankaanpää et al., 1998; Yerys et al., 2002), no published studies have investigated hip extension force in individuals with LSI during PHE. To the best of our knowledge, no study has investigated back and hip extensor activity and hip extension force in individuals with LSI during PHE. Because back and hip extensor muscle activity are altered during PHE in LBP subjects (Arab et al., 2011), it is worthwhile to compare

ACCEPTED MANUSCRIPT muscle activity in individuals with LSI and asymptomatic subjects. Therefore, the objective of this study was to investigate potential differences in back and hip extensor muscle activity and hip extension force during PHE in individuals with LSI and asymptomatic subjects. We hypothesized that LSI individuals will show different back and hip extensor muscle activity and hip extension force

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compared to asymptomatic individuals.

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1. Methods

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2.1 Subjects

At the beginning, 120 individuals with back pain who had positive in radiographic screening were volunteered in this study. Among them, 17 did not report concordant pain at discography, 28 did not meet the slip criteria (lesser than 3 mm slip), 19 people did not meet translation criteria and 20 people did not meet 2 clinical tests criteria. Therefore, only 36 subject data which met all inclusion

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criteria were included for data analysis. For asymptomatic group, 54 people without known back pain agreed to participate in this study. Among them, 28 subjects were excluded secondary to abnormal finding in the radiographic screening tests such as degenerative discopathy in MRI (Fig.1). Sixty-two

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women (36 subjects with LSI and 26 asymptomatic subjects) were recruited from an orthopedic clinic. All subjects had medical imaging, including plain radiography, magnetic resonance imaging, and

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discography procedures, completed by the same orthopedic spine surgeon, and each subject underwent two clinical tests (passive lumbar extension test and lumbar extension load test) completed and interpreted by an experienced physiotherapist in musculoskeletal conditions (Rabin et al., 2013). Table 1 shows the inclusion/exclusion criteria for the study. To control confounding variables, the study recruited 26 age- (± 5y), weight- (± 3kg), and height- (± 3cm) matched control subjects without LSI. The data of the patients with LSI are showed in Table 2, also participant demographics are presented in Table 3. Due to the small sample size, and to control for confounding variables such as gender differences, only women were included in the study. Detailed descriptions of study procedures

ACCEPTED MANUSCRIPT and safety measures were provided to all subjects, and each subject signed an informed consent form

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approved by the Medical Ethical Committee of the Seoul-chuk Hospital.

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Fig. 1. Flow diagram of patient recruitment.

Table 1

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Presenting pain:

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Inclusion and exclusion criteria for all subjects LSI Group Inclusion criteria

Asymptomatic Group · No history of LBP in the previous 12

· Nonradicular central LBP for >3 months (Pitkänen et al., 2002; Silfies et al. 2005)

months · Negative results on the medical imaging

Medical imaging examination: · Combination of >3 mm slip and >3 mm translation on plain radiographs (Iguchi et al., 2011) · Degenerative disc disease on MRI with positive low pressure discography at 1 or more corresponding lumbar levels (Silfies et al. 2005; López et al., 2012)

examination and clinical tests

ACCEPTED MANUSCRIPT Clinical tests (Rabin et al., 2013): · Passive lumbar extension test (PLET) · Lumbar extension load test (LELT) Exclusion criteria

Shortening of the hip flexors (positive Thomas test) History of fractures or surgery in the lumbar spine or hip joints Structural deformities or neurological disorders Significant weakness in the hip muscles

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Inability to perform hip extension

Table 2 Data of the patients with LSI

L4-5 L5-S1 L3-4 L5-S1 L5-S1 L4-5 L3-4 L5-S1 L5-S1 L5-S1 L3-4 L3-4 L3-4 L3-4 L4-5 L3-4 L5-S1 L3-4 L3-4 L4-5 L4-5 L3-4 L5-S1 L4-5 L4-5 L5-S1 L3-4 L3-4

Slip (mm) 4.3 3.2 3.5 3 3.2 4.2 3.4 3.2 3 3.1 3.4 3.6 3.4 3.4 3.8 3.4 3.1 3.7 3.5 3.6 3.4 3.2 3 4.1 3.7 3.1 3.3 3.3

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Levels

Translation (mm) 4.7 3.5 3.7 3.3 3.6 4.4 3.8 3.5 3.4 3.6 3.8 4.1 3.7 3.8 4.3 3.7 3.5 4.1 3.9 4 3.7 3.6 3.5 4.5 4.1 3.6 3.7 3.6

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Subjects number

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Abbreviations: LBP = low back pain; MRI = magnetic resonance imaging Data of the patients with LSI

(n= 36)

Concordant pain on discography (VAS score) 5 3 4 3 3 5 4 4 3 4 4 4 5 4 5 4 3 4 4 4 4 4 4 5 5 4 5 4

ACCEPTED MANUSCRIPT L4-5 L4-5 L5-S1 L3-4 L5-S1 L5-S1 L5-S1 L4-5

3.8 3.4 3.2 3.5 3.2 3.1 3 3.6

4.3 3.9 3.5 3.8 3.8 3.6 3.4 4.1

5 4 3 3 4 3 4 5

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29 30 31 32 33 34 35 36

Table 3

(n= 62)

Parameters

LSI Group (n=36)

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Subject demographics

Asymptomatic Group (n=26)

P-value

28.84 ± 3.42

29.04 ± 2.83

0.717

Weight (kg)

56.01 ± 5.24

57.87 ± 6.92

0.536

Height (cm)

161.03 ± 3.69

160.90 ± 4.28

0.912

76.04 ± 5.28

0.864

Leg length (cm) VAS (x/11)

76.28 ± 5.9 5.31 ± 0.8

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Age (years)

Abbreviations: LSI = lumbar segmental instability; VAS = visual analog scale

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2.2 Clinical tests

Prior to the experiment, two clinical tests were used to check for signs of LSI (Rabin et al.,

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2013). In the passive lumbar extension test (PLET), the subject lies prone and the examiner lifts both of the subject’s legs approximately 30 cm off the table, while applying slight traction to both legs.

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Perceived LBP or discomfort is considered a positive test result. In the lumbar extension load test (LELT), the subject lies prone and the examiner applies a posterior-to-anterior pressure to the lumbar spine in both neutral and extended spine positions. An LBP in the neutral position that decreases in the extended position is considered a positive test result. Sensitivity and specificity of the PLET are 84.2% and 90.4%, respectively (Kasai et al., 2006) while reliability of the LELT to assess LSI remains uncertain (Rabin et al., 2013). Therefore, a positive result for both clinical tests was required for a subject to be included in the LSI group. 20 subjects among 120 recruited volunteers were excluded from clinical tests (Fig. 1).

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2.3 Instrumentation

(1) A digital force gauge (Model 9200, Aikoh Engineering CO., LTD, Osaka, Japan) was

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used to record hip extension force.

(2) A digital inclinometer (Dualer IQ; J Tech Medical Industries, Heber City, UT, USA) was

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used to measure hip angles during PHE.

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2.4 Visual analog scale (VAS)

An 11-point visual analog scale (VAS) (0 = no pain to 10 = worst imaginable pain) was used to measure pain intensity during PHE. The VAS provides reliable and valid data about pain in patients with lumbopelvic instability (Brokelman et al., 2012).

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2.5 EMG recording and data analysis

Muscle activity was measured in the dominant leg using the Noraxon TeleMyo 2400T

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system (Noraxon, Inc., Scottsdale, AZ, USA) with two bipolar Ag/AgCl surface electrodes (Norotrode 20TM, Myotronics-Noromed, Inc, WA, USA) during PHE. Before placing the electrodes,

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the skin is shaved and abraded and then cleaned with isopropyl alcohol. All electrodes were placed with an interelectrode distance of 2 cm and aligned parallel to the underlying muscle fibers. For the erector spinae, electrodes were placed approximately 2 cm lateral to the spinous process of L1 parallel to the spine on the muscle belly. For the gluteus maximus, electrodes were placed halfway between the greater trochanter and the sacrum on an oblique angle. For the biceps femoris, electrodes were attached halfway between the gluteal fold and the knee joint (Cram et al., 1998). The reference electrode was attached to the right anterior superior iliac spine (ASIS). Surface electrodes were sampled at 1000 Hz. The electromyographic (EMG) signal was amplified with an overall gain of

ACCEPTED MANUSCRIPT 1785.7 and digitized using MyoResearch Master Edition 1.06 XP software (Noraxon, Inc., Scottsdale, AZ, USA). Band-pass (20 – 450 Hz) and notch filters (60 Hz) were used. Raw EMG signals were processed into the root mean square (RMS). Data were normalized by calculating the mean RMS of three trials of 5-second reference voluntary contractions (RVC) for each muscle. The RVC for the

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erector spinae was calculated while the subjects were prone with both legs raised 5 cm off the examination table and knees at a 90° angle. The RVC for the biceps femoris was calculated while subjects performed 30° of knee flexion in the prone position with a 3-kg sandbag attached to the distal

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portion of the shank. For the gluteus maximus, the RVC was calculated while subjects performed approximately 10° of hip extension with the knee flexed to 90° with a 3-kg sandbag attached to the

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distal portion of the shank. When testing PHE, the EMG signal was collected for 5-seconds while the hip was held at 10° of hip extension. Data for each trial were expressed as a percentage of the calculated mean RMS of the percentage of a reference voluntary contraction (% RVC), and the mean %

2.6 Procedures

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RVC of three trials was used for analysis.

EMG activation patterns of the back and hip extensor muscles and hip extension force during

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PHE were investigated in individuals with LSI and asymptomatic subjects. Before data collection, each subject had 10 practice trials to be familiar with the experimental procedure. Subjects were asked

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to lie in a prone position on a table with their head slightly extended to maintain normal breathing and with their upper trunk, pelvis, and feet aligned in a straight line (Oh et al., 2007). After they heard a start signal, they extended their dominant leg to a point of 10° hip extension to a target bar and held the position for 5 seconds. A target bar was placed at the level of 10° hip extension, as measured using an inclinometer. The EMG and maximal hip extension force were recorded while the subject maintained 10° hip extension (Fig. 2). A verbal command was also given to focus the subject’s attention and minimize the influence of velocity in raising the leg. Each subject performed three trials of maximal hip extension with a 1-min rest between repetitions.

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Fig. 2. Instrumental set up for EMG and force measurement. A. Before hip extension. B. At 10° hip

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extension. * Mark is digital force gauge.

2.7 Statistical analysis

Statistical analyses were performed with SPSS version 18.0 (SPSS Inc., Chicago, IL, USA).

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Data are expressed as mean ± standard deviation (SD). Independent t-tests were used to compare groups (LSI group versus asymptomatic group). For all tests, the alpha level was set at 0.05.

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3. Results

There were significant differences in muscle activity between the LSI and asymptomatic

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groups during PHE (Table 4). Subjects in the LSI group had significantly greater muscle activity in the erector spinae, gluteus maximus, and biceps femoris compared to subjects in the asymptomatic group. Hip extension force was also different between the two groups (Table 4). Subjects in the LSI group exhibited significantly less hip extension force compared to subjects in the asymptomatic group during PHE.

Table 4. Clinical findings Parameters

LSI group (n=36)

Asymptomatic group (n=26)

P value

ACCEPTED MANUSCRIPT Muscle activity (% RVC) Erector spinae

71.2 ± 17.8

35.4 ± 10.6

0.000*

Gluteus maximus

35.3 ± 23.9

24.6 ± 10.1

0.020*

Biceps femoris

96.3 ± 12.4

64.3 ± 23.1

0.000*

Hip extension force (N)

121.2 ± 4.0

0.000*

5.31 ± 0.8

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VAS (mm)

175.7 ± 6.4

*p < 0.05 Abbreviations: LSI = lumbar segmental instability; N = newton; RVC= reference voluntary contraction; VAS = visual analog scale

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4. Discussion

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To the best of our knowledge, this is the first study to investigate differences in back and hip extensor muscle activity and maximum hip extension force during PHE in individuals with LSI and asymptomatic subjects. As hypothesized, we found that during PHE, subjects with LSI exhibited significantly greater erector spinae, gluteus maximus, and biceps femoris EMG activity than asymptomatic subjects; however, maximum hip extension force was significantly lower in subjects

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with LSI than in asymptomatic subjects. These findings are in line with a recent study that reported greater activation of the erector spinae, gluteus maximus, and biceps femoris in subjects with LBP compared to asymptomatic subjects during PHE (Arab et al., 2011). One possible explanation for

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increased EMG activity in subjects with LSI is that more muscle activation may be required to compensate for decreased passive stability in the lumbar region (de Groot et al., 2008; Arab et al.,

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2011). Panjabi et al. (1992) theorized that dysfunction of the passive subsystem as a result of LSI is likely to be compensated for with enhanced muscle activation. The increase of muscle activity of the back and hip extensors in the LSI group may be explained by increased segmental movement due to disc degeneration (Li et al., 2011; Ibarz et al., 2013). Although segmental movement of the lumbar spine was not measured directly in this study, the influence of disc degeneration on segmental movement has been measured during application of a controlled load to produce motion in a finite element simulation model (Ibarz et al., 2013). In that study, disc degeneration was found to cause increased segmental movement at all lumbar spinal levels and in all movements (flexion, extension,

ACCEPTED MANUSCRIPT lateral flexion, and rotation). Li et al. (2011) showed that disc degeneration can alter the movement of the facet joints not only at the level of disc degeneration, but also at adjacent levels. The movements were measured using magnetic resonance imaging and dual fluoroscopic imaging during functional trunk activities. Greater muscle activity of the back and hip extensors in the LSI group may be

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necessary to generate the force required to accommodate larger segmental movements during PHE. However, the greater and more sustained muscle activation would increase loads on the spinal joints and tissues, which ultimately results in LBP (van Dieen et al., 2003). Eventually, these changes in the

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active subsystem can give rise to potential alterations in the motor control pattern of back and hip extensor recruitment during PHE.

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The gluteus maximus and hamstrings must be coordinated synergistically to generate an adequate level of hip extension force to achieve lumbar stability during PHE (Chance-Larsen et al., 2010). However, despite greater hip extensor muscle activation, subjects with LSI in this study produced a significantly lower hip extension force than asymptomatic subjects. Similarly, De Groot et al. (2008) found that asymptomatic subjects generated greater hip flexion force at relatively lower

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level hip flexor EMG activity than subjects with pregnancy-related lumbopelvic instability during active, straight leg raising. These findings suggest that compared to asymptomatic subjects, those with lumbopelvic instability stabilize their lumbopelvic region less effectively with muscular contractions

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to achieve an equivalent level of performance. Furthermore, Kankaanpää et al. (1998) reported that the relative weakness and fatigability of the hip extensor muscles of women with LBP may be a

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potential contributing factor in LBP. Therefore, insufficient hip extension force in the LSI group may reflect diminished stabilizing mechanisms while maintaining lumbopelvic stability during PHE. This study has several limitations. First, because only young women were recruited, the

findings of this study cannot be generalized to men or older individuals. Second, because lumbopelvic movement during PHE was not measured, it is not possible to exclude the influence of lumbopelvic movement in the results. Third, pain may be a confounding factor for EMG normalization using reference voluntary contraction methods because EMG activity and force production (Hodges and Moseley, 2003) can be inhibited by perceiving pain, even though the subjects in the LSI group did not

ACCEPTED MANUSCRIPT report increased pain during the testing procedure. Finally, this cross sectional study investigated differences in muscle activity and force between individuals with LSI and asymptomatic subjects; further longitudinal studies are required to investigate the effects of intervention, including exercise,

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on back and hip extensor muscle activity and hip extension force in individuals with LSI.

5. Conclusion

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This study investigated potential differences in back and hip extensor muscle activity and hip extension force during PHE in subjects with LSI and asymptomatic subjects. Subjects in the LSI

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group developed significantly greater muscle activity in the back and hip extensors and significantly less hip extension force than did subjects in the asymptomatic group during PHE. These findings suggest that during PHE, subjects with LSI have differences in back and hip extensor muscle activity

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ACCEPTED MANUSCRIPT Acknowledgments This work was supported by the National Research Foundation of Korea Grant funded by the

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Korean Government(NRF-2013S1A5B8A01055336).