Low back and lower-limb muscle performance in male and female recreational runners with chronic low back pain.

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Low Back and Lower Limb Muscle Performance in Male and Female Recreational

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Runners with Chronic Low Back Pain

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Congcong Cai, MSc1,2 and Pui W. Kong, PhD1

Journal of Orthopaedic & Sports Physical Therapy® Downloaded from www.jospt.org at UCSF Lib & CKM/RSCS Mgmt on April 28, 2015. For personal use only. No other uses without permission. Copyright © ${year} Journal of Orthopaedic & Sports Physical Therapy®. All rights reserved.

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Nanyang Technological University, 1 Nanyang Walk, Singapore 637616.

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378 Alexandra Road, Singapore 159964.

Physical Education and Sports Science Academic Group, National Institute of Education,

Physiotherapy, Rehabilitation Department, Alexandra Hospital-Jurong Health Service,

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Corresponding Author:

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Pui W. Kong

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Physical Education and Sports Science Academic Group

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National Institute of Education

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Nanyang Technological University

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1 Nanyang Walk

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Singapore 637616

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Tel: (65) 6219 6213

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Fax: (65) 6896 9260

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Email: [email protected]

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This study was funded by the Internal Grant of Alexandra Hospital. The funding source

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did not play a role in the investigation.

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Word Count = 246 (abstract), 3098 (text)


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Financial Disclosure and Conflict of Interest: We affirm that we have no financial

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affiliation (including research funding) or involvement with any commercial organization

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that has a direct financial interest in any matter included in this manuscript, except as

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disclosed in an attachment and cited in the manuscript. There is no any other conflict of

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interest.

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Abstract

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Study Design: Controlled Laboratory Study; Cross-sectional.

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Objective: To compare lumbar extensor muscle fatigability, lumbar muscle activation,

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and lower limb strength between male and female runners with chronic low back pain

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(LBP) and healthy runners.

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Background: Little is known about muscle performance in runners with chronic LBP.

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Methods: 18 recreational runners with chronic LBP (9 males and 9 females; mean age =

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27.8 years) and 18 healthy recreational runners (9 males and 9 females; mean age = 24.6

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years) were recruited. The median frequency slopes for bilateral iliocostalis and

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longissimus were calculated from electromyographic signals captured during a 2-minute

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Sorenson Test. The thickness changes of the transversus abdominis and lumbar

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multifidus between resting and contraction were measured using an ultrasound scanner.

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Peak concentric torque of the bilateral hip extensors,hip abductors, and knee extensors

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were measured using an isokinetic dynamometer at 60˚/s. The average values for both

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sides were used for statistics analysis.

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Results: When averaged across genders, peak knee extensor torque was 12.2% lower in

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the LBP group compared to the healthy group [mean difference (95% CI) = 0.29 (0.06-

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0.53) Nm/kg, p = .016]. Male runners with chronic LBP exhibited smaller lumbar

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multifidus thickness changes compared to healthy male runners [mean difference (95%

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CI) = 0.13 (0.01-0.25) cm, p = .033]. No other group differences were observed.

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Conclusion: Runners with chronic LBP exhibited diminished knee extensor strength

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compared to healthy runners. Male runners with chronic LBP demonstrated additional

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deficits in lumbar multifidus activation.

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Key Words: Rehabilitative Ultrasound Image; electromyography; isokinetic strength;

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muscle activation.

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Word Count (Abstract) = 246

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Low Back Pain (LBP) is a common problem in runners worldwide. In the southern

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United States, the prevalence of LBP in recreational runners has been reported to be as

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high as 13.6%,50 and low back injuries have been reported to account for about 7% of all

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running injuries.11 Running injuries of the lumbar spine and pelvis can be debilitating,

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requiring prolonged periods of rehabilitation.9, 13, 26

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In the general population, it has been reported that person with LBP exhibit muscle

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performance deficits. Deficits in lumbar extensor muscle strength and endurance12, 19, 20, 28,

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37, 43, 45, 48

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abdominis18 have been reported. Persons with chronic LBP also have been characterised

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by inferior gluteus maximus endurance,23 diminished flexibility of the knee and hip

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flexors,4 and inhibition of knee extensor maximal voluntary contraction.47 These deficits

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in lower extremity muscle performance have been proposed to further affect LBP.35

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Although the relationship between lower extremity muscle performance deficits and LBP

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has not been specifically studied in runners, the biomechanical demands during running

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suggest that such deficits, if they exist, may be more detrimental than in non-runners.

smaller lumbar multifidus size16 and delayed onset of the transversus

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Running is a very dynamic activity, with the lower limbs and the lumbar spine playing an

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important role.38,41 Biomechanically, the total axial load on the lumbar spine during

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running is more than 3 times the weight of the upper body above the 5th lumbar segment.3

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The mid lumbar spine must cope with compressive loads in the range of 2.7-5.7 times

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body weight immediately following foot strike.3 Repetitive hyperextension of the lumbar

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spine during running has been thought to be a possible mechanism of LBP development

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in runners.1,

13, 21

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minimizing the transmission of force to the pelvis and spine.40 Weakened muscles of the

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pelvis and lower limbs may fail to adequately absorb impact forces and therefore increase

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force transmission to the spine.35

During running, the ankle, knee and hip act as a linked system

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While deficits of lumbar extensor endurance, lumbar muscle activation, and lower limb

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strength are widely reported in the general population with LBP, it is unclear whether

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such deficits are present in runners with LBP. A better understanding of such muscular

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characteristics of runners with chronic LBP may contribute to the future screening,

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diagnosis and development of runner-specific exercise rehabilitation programs. Thus, the

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primary purpose of this study was to compare lumbar extensor muscle fatigability,

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lumbar muscle activation, and lower limb strength between male and female recreational

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runners with chronic low back pain (LBP) and healthy recreational runners. It was

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hypothesized that the lumbar extensor muscle endurance, lumbar muscle activation and

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lower limb muscle strength would be diminished in recreational runners with LBP.

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Methods

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Participants

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Eighteen recreational runners with non-specific chronic LBP referred from the

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orthopaedic outpatient specialist clinic from Alexandra Hospital were recruited (9 males

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and 9 females). Eighteen healthy recreational runners (9 males and 9 females) also were

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recruited. The sample size of 36 was estimated by a priori power analysis (power = 80%,

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α = .05, two-tailed tests). The effect sizes for transversus abdominis thickness and lumbar

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extensor muscle median frequency differences between persons with chronic LBP and

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healthy controls have been reported to be 1.26 and 1.025 respectively. A more

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conservative effect size of 1.0 was used in our calculations.


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The inclusion criteria for subjects in the LBP group were as follows: 1) age range 21 to

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45 years, 2) body mass index ranged 18-25 kg/m2, 3) reported LBP for > 3 months and
4/10 (average rating during past one week), 2) spine

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fracture, disc herniation, or signs of nerve root compression, 3) metabolic or hormonal

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abnormalities, 4) history of spine surgery, 5) current or previous history of lower limb

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fracture, tendon rupture, hip and knee arthritis, ligament laxity, , 6) high fear-avoidance

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beliefs (Fear Avoidance Beliefs Questionnaire score: physical activity > 12; work > 1910,

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), 7) employment requiring heavy lifting and 8) current use of pain medication.

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The study protocol was approved by the Nanyang Technological University Institutional

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Review Board and the National Healthcare Group Domain Specific Review Board.. All

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participants who volunteered for this study provided written informed consent.

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Procedures 7


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All participants were asked to complete a Patient Specific Functional Scale (PSFS)46 for

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running and to report their pain intensity during running as measured by a numerical pain

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scale. Height and weight measurements were then obtained, followed by muscle

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performance variables listed below.

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Lumbar extensor muscle fatigability

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Bilateral iliocostalis and longissimus activation signals during a 2-minute Sorenson Test

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were captured using surface electromyography (EMG) sampled at 1,000 Hz (Bagnoli™

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Desktop EMG system, Delsys® Boston, MA, US). The electrodes for longissimus were

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placed 2 cm lateral to the L1 spinous process, parallel to the spine (Figure 1a).5 The

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electrodes for the iliocostalis were placed 4.5 cm lateral to the L3 spinous process,

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parallel to a straight line from posterior superior iliac spine to lateral border of the 12th

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rib (Figure 1a).7, 44

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The Sorenson test required participants to lie on an examining table in the prone position

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with the upper edge of the iliac crests aligned with the edge of the table. The lower body

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was fixed to the table by 3 straps, located around the pelvis, knees, and calf.(Figure 1b).36

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With the arms folded across the chest, participants were asked to maintain the upper body

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in a horizontal position without neck extension for 2 minutes. Participants were allowed

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to terminate the test at any time if pain became unbearable. The test also was terminated

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if participants failed to maintain the upper body in a horizontal position. Raw EMG data

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were band-pass filtered at 20-450 Hz, and then analysed in the frequency domain. The

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median frequency was calculated from the power density spectrum obtained using the

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fast Fourier transform technique with a Hamming windowing of 0.1 seconds. The slope

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of the median frequency (MFS) was calculated for each muscle.


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Lumbar muscle activation

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The thickness of the transversus abdominis and lumbar multifidus was measured using an

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ultrasound scanner (LOGIQ P5, GEHC, Milwaukee, WI, US). Images of the transversus

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abdominis muscle were captured at rest and during a sub-maximal contraction induced by

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an active straight leg raise (Figure 2a).27 Similarly, images of the lumbar multifidus were

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captured at rest and during a sub-maximal contraction induced by diagonal arm raise with

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a 0.8-kg weight held in the hand (Figure 2b).24 The side tested first was determined

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randomly. An average reading of 3 trials for each muscle group was used for subsequent

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analysis.

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The muscle thickness changes as reflected by muscle activation were calculated as the

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thickness during contraction subtracted by the resting thickness (Figures 2c and 2d).

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Previous studies have demonstrated the importance of normalizing muscle thickness

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change to body mass using allometric scaling.33, 42 Therefore we applied this method to

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scale the thickness changes of the lumbar multifidus and transversus abdominis using the

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following equation:34 a=S/mb

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(1)

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where a = allometric-scaled muscle thickness changes, S = muscle thickness changes, m

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= body mass, and b = derived allometric parameter.34 The allometric parameter was the

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slope of the linear regression line between the log transformed body mass and log

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transformed muscle thickness change.22, 34 The allometric parameters for the transversus

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abdominis were 0.077 and -0.030 for dominant and non-dominant body sides respectively,

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and 0.037 and 0.121 for the lumbar multifidus (dominant and non-dominant body sides

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respectively).

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Lower limb muscle strength

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Peak torque of bilateral hip extensors, hip abductors, and knee extensors were measured

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using an isokinetic dynamometer (Biodex system 4 Pro, Biodex Corp., Shirley NY, US).

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A concentric contraction speed of 60/s was used. The knee extension test was performed

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in the seated position (Figure 3a). The test leg was secured to the dynamometer crank arm

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with a Velcro strap positioned 1 inch above the ankle, with the hip and thigh stabilized to

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the testing chair with Velcro straps. The lateral epicondyle of the femur was used as the

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anatomical reference to which the axis of the dynamometer was aligned. The

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flexion/extension range of motion was set from 0 to 90 of flexion (0 = full extension).

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The hip strength tests were performed in a standing position (Figures 3b and 3c), with the

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test leg secured to the dynamometer crank arm with a Velcro strap positioned 1 inch

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above the knee. The greater trochanter of the femur was used as the anatomical reference

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to which the axis of the dynamometer was aligned. A stable handhold was provided to the

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participants to ensure stability. The flexion/extension range of motion was set from 90

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of flexion to 10 of extension and the abduction/adduction range of motion was set from

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0 to 30 of abduction. The test sequence of body sides was determined randomly. The

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peak torque values were normalized to body mass. The average value of the 3 trials was

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used for analysis.

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Statistical Analysis

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Since bilateral differences were not observed for any of the variables of interest, the

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average values from both sides were used for statistical analyses (SPSS 19.0). A general

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linear model was used to detect differences in muscle performance variables between the

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chronic LBP and control groups. The dependent variables included lumbar extensor

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muscle fatigability (MFS for iliocostalis and longissimus), lumbar smuscle activation

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(allometric-scaled thickness changes of lumbar multifidus and transversus abdominis

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between resting and contraction), and lower limb muscle strength (average peak torque of

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the hip extensors, hip abductors and knee extensors). Group (LBP or control) was entered

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as Fixed Factor. To explore potential sex differences, gender also was entered as a fixed

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factor. Age was used as a covariate as the LBP group was significantly older than the

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control group. The interaction between group and gender also was examined in the model.

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The observed means (SD), estimated marginal means and mean differences (95% CI)

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were reported. The significance level was set at .05.

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Results

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Participant Characteristics

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Compared to the control group, The LBP group was older (p = .042), had higher fear-

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avoidance beliefs (p = .012), and a lower PSFS score for running (p < .001) (Table 1). On

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average female participants were shorter in height than their male counterparts (p=.001).

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No other differences in physical characteristics or demographics were found.

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Muscle Performance

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Muscle performance variables for the low back and lower limbs muscles for both groups

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are presented in Table 2. In regards to lumbar extensor muscle fatigability (MFS of

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longissimus and iliocostalis), no significant group main effects, or interactions (condition

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× gender) were observed. With respect to lumbar muscle activation, there was a

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significant group × gender interaction (p =.018) for lumbar multifidus thickness changes.

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Post-hoc analysis revealed that the reduction in thickness change among runners with

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LBP runners only occurred in males [LBP = 0.330 (0.109) cm, Healthy = 0.590 (0.191)

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cm, p < .05]. No significant group main effect or interaction was found for changes in

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transversus abdominis thickness.

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Regarding lower limb strength, knee extensor peak torque was significantly lower in the

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LBP group [Mean difference (95% CI) = 0.29 (0.06-0.53) Nm/kg, p=.016] compared to

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the control group. The interaction for this variable (condition × gender) was not

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significant (p = .323). No significant group main effects or interactions were observed for

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hip abduction or hip extension strength .

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Discussion

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The current study compared muscle performance characteristics of the back and lower

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limb muscles in recreational runners with and without chronic LBP. On average, knee

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extensor torque deficits were found in the LBP group, and lumbar multifidus activation

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deficits, as reflected by smaller thickness changes during submaximal contractions, only

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were observed among male runners with LBP. There were no other differences in muscle

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performance between the 2 groups.


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In our study, the longissimus and iliocostalis fatigability as measured by changes in MFS

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did not differ between the chronic LBP and healthy runners. This is in contrast with

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previous studies performed on athletes with chronic LBP participating in various sports.2,

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horizontal position was shorter in athletes with chronic LBP compared to healthy controls.

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The small and heterogeneous sample size of 8 athletes participating in 3 different types of

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sports activities (gymnastics, swimming and basketball), makes it difficult to interpret

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their results. Another study measured lumbar extensor fatigue recovery in rowers using

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EMG and reported that rowers with chronic LBP had significant slower muscle power

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recovery as measured by MFS.25 Since the nature of rowing is very different from that of

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running, it is difficult to compare these previous findings with the current study.

Ashmen et al.2 reported that the holding duration of the unsupported upper body in a

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We observed that male runners with chronic LBP exhibited reduced lumbar multifidus

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activation as reflected by smaller changes in muscle thickness between resting and a

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submaximal contraction. Our findings are consistent with Lee et al., who reported

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persons with chronic LBP exhibit reduced lumbar multifidus cross-section area as

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measured with ultrsound.30 As suggested previously, we postulate that the observed

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muscle activation deficit may be due to an inhibition from perceived pain via a long-loop

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reflex pathway30 since our runners with LBP had a relatively low level of pain

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(Numerical Pain Score = 2.39). We were unsure, however, why such deficits were not 13

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observed in female runners with chronic LBP. We speculate that the smaller size of the

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lumbar multifidus in females could make the deficit, if present, less obvious than that in

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males.


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We did not find a significant difference in the transversus abdominis thickness change

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between the runners with chronic LBP and the control subjects. In the literature, mixed

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findings have been reported with respect to transversus abdominis activation. In the

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general LBP population, one study found no differences in transversus abdominis

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thickness changes induced by simulated lower limb weight-bearing at 50% of body

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weight between LBP and healthy subjects,15 but another study reported smaller thickness

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changes in LBP subjects during lower limb isometric loading at 7.5% and 15% of body

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weight.8 Unfortunately, the authors of the latter study did not report the absolute

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thickness changes which was is recommended for clinical measurements due to large

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measurement error.27 The varying results in the literature make direct comparisons to our

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study findings difficult. Moreover, there are variations in the methods employed to

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measure transversus abdominis activation among studies, possibly leading to varied

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results.

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We found diminsished knee extensor strength in our runners with chronic LBP when

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compared to the control subjects. In literature, there is no information on lower limb

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strength in runners with chronic LBP, however an association between knee extensor

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strength deficits and trunk weakness in patients with disc herniation and other chronic

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LBP populations have been reported.17,

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endurance reduction as detected by EMG also have been reported in golfers with chronic

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LBP.47 In a study of runners with chronic LBP, increased knee joint stiffness during

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running has been reported when compared to healthy controls14. During running, the

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quadriceps contract eccentrically following initial contact, playing an essential role in

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shock absorption.41 Weakness of the knee extensors may increase knee joint stiffness

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during running and therefore reduce capacity for shock attenuation. The shock from

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ground may then transmit to the low back, increasing lumbar spine stress.

Knee extensor inhibition and trunk muscle

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We did not find any differences in hip extensor and abductor strength between the

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runners with chronic LBP and the control group. This is in contrast with previous studies

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that have reported that persons with LBP population exhibit delayed activation and

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endurance deficits of the hip extensors.23,

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abductor weakness and LBP has been reported.39 It should be noted that previous studies

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were performed on older and more sedentary populations and that hip strength was

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measured in a sitting position. We adopted a one-leg standing protocol to assess hip

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torque as this body posture better approximates the position of the hip during running.

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Thus, it is difficult to directly compare our results with previous studies. On the other

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hand, it is likely that the functional characteristics of the hip muscles in runners are

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different from those of the general population. Hip extensor and abductor strength has

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been described as being important for power generator and stabilization during running.41

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The frequent use of hip muscles in chronic LBP runners could make any muscle

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functional deficit less obvious.

31

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In addition, an association between hip


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There are certain limitations with our study that need to be considered. First, we did not

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measure biomechanical characteristics such as ground reaction forces and lower

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extremity kinematics during running. Future studies should obtain such data to better

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understand the relationship between muscle performance characteristics and LBP. Second,

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the current study design did not incorporate a non-runner LBP group to determine if the

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observed deficits were specifically related to runners. Third, the age range of our subjects

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was relatively narrow (21 to 38 years of age), limiting the generalization of our findings

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to younger and older populations. Fourth, the chronic LBP subjects in our study had a

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relatively high level of functional activity as illustrated by a PSFS of 7.9/10 during

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running. Thus, our findings may not apply to runners with lower functional activity levels.

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Fifth, our subjects’ usual running speed and pace were not recorded. This is important as

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running speed has been reported to affect the degree of lumbar spine lordosis during

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running,13, 32 which could potentially contribute to back injury. Finally, we statistically

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compared several muscular performance variables without adjusting the α-value. Since

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we reported unadjusted nominal p-values throughout, readers should be aware of the

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increased chance of type 1 error when interpreting the study findings.

330 331

Conclusion

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Runners exhibiting chronic LBP exhibited weaker knee extensors compared to healthy

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runners. Activation deficits in the lumbar multifidus were observed among male runners

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with LBP, but not in females. No functional deficits were found in lumbar extensor

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fatigability, transversus abdominis activation or hip muscle strength.

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339

Key Points


340 341

Findings: Our results identified diminished knee extensor strength in runners with

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chronic LPB. Decifits in lumbar multifidus activation were also observed in male runners

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with chronic LBP.

344

Implications: Our study findings may contribute to our understanding of causes of LBP

345

pain in runners and the development of rehabilitations program for runners with chronic

346

LBP.

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Caution: The participants with chronic LBP in our study had relatively high level of

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functional activity with an average PSFS of 7.9/10 during running. Thus, our findings

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may not apply to runners with lower functional activity levels.

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Mean (SD) p-values Chronic LBP Healthy group gender group × gender runners n=18 runners n=18 Variable Age (yrs) M 29.6 (7.3) 25.6 (4.2) .770 .613 .042 F 26.0 (2.6) 23.6 (2.5) Height (cm) M 171.3 (4.7) 172.1 (7.0) .734 .506 .001 F 165.2 (8.4) 163.0 (4.2) Body Mass Index (kg/m2) M 21.5 (2.4) 21.7 (2.0) .604 .923 .468 F 22.0 (2.1) 21.1 (2.1) Running Frequency (times per week) M 2.8 (1.0) 3.2 (1.0) .107 .107 1.000 F 2.3 (0.5) 2.8 (0.7) Running Distance per Time (km) M 3.5 (0.9) 4.6 (0.7) .134 .240 .134 F 3.7 (0.7) 3.7 (1.4) PSFS M 8.1 (0.6) 10.0 (0.1) .338 .338

Classification of Chronic Back Muscle Degeneration after Spinal Surgery and Its Relationship with Low Back Pain.

Chronic low back pain patient and spouse.

Accelerometer-Determined Physical Activity and Clinical Low Back Pain Measures in Adolescents With Chronic or Subacute Recurrent Low Back Pain.

Therapeutic ultrasound for chronic low-back pain.

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Corticosteroid injections for chronic low back pain.

TENS for chronic low back pain.

Health utilities for chronic low back pain.

TENS for chronic low-back pain.

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Personality traits in patients with acute low-back pain. A comparison with chronic low-back pain patients.

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Chiropracters and low back pain.

Lumbar disc screening using back pain questionnaires: oswestry low back pain score, aberdeen low back pain scale, and acute low back pain screening questionnaire.

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Sympathetic Dysfunction in Patients With Chronic Low Back Pain and Failed Back Surgery Syndrome.

Disability and disability benefit seeking in chronic low back pain.

Inspiratory muscle training affects proprioceptive use and low back pain.

Pain intensity measurement in chronic low back pain.

Diagnostic uncertainty and recall bias in chronic low back pain.

Industrial back belts and low back pain: Mechanisms and outcomes.