Spinal muscle evaluation using the Sorensen test: a critical appraisal of the literature

doi:10.1016/j.jbspin.2004.08.002

Joint Bone Spine

Volume 73, Issue 1, January 2006, Pages 43-50

https://doi.org/10.1016/j.jbspin.2004.08.002 Get rights and content

Abstract

The first test for evaluating the isometric endurance of trunk extensor muscles was described by Hansen in 1964. In 1984, following a study by Biering-Sorensen, this test became known as the “Sorensen test” and gained considerable popularity as a tool reported to predict low back pain within the next year in males. The test consists in measuring the amount of time a person can hold the unsupported upper body in a horizontal prone position with the lower body fixed to the examining table. This test has been used in many studies, either in its original version or as variants. Although its discriminative validity, reproducibility, and safety seem good, debate continues to surround its ability to predict low back pain; in addition, the gender-related difference in position-holding time remains unexplained and the influence of body weight unclear. A contribution of the hip extensor muscles to position holding has been established, but its magnitude remains unknown. The influence of personal factors such as motivation complicates the interpretation of the results. Despite these drawbacks, the Sorensen test has become the tool of reference for evaluating muscle performance in patients with low back pain, most notably before and after rehabilitation programs.

Introduction

Despite growing research efforts, nonspecific low back pain remains a major public health burden throughout the industrialized world. Epidemiological data indicate an annual prevalence of about 39–54% [1], [2] and a lifetime prevalence of 60–65% [1], [2], [3]. Costs to society stem mainly from chronic forms, which account for only 5–10% of cases [4], [5]. Chronic nonspecific low back pain results in both physical and psychological deconditioning that traps the patient in a vicious circle characterized by decreased physical performance, exacerbated nociceptive sensations, impaired social functioning, work disability, and depression. The physical component of deconditioning involves both stiffness of the lumbar spine-pelvic-femoral unit, decreased muscle strength and endurance, loss of cardiorespiratory adjustment to physical exertion, and neuromuscular inhibition (kinesiophobia) [6].

Several studies suggest that patients with chronic nonspecific low back pain may benefit from an active multidisciplinary approach involving an individually tailored reconditioning program [6], [7], [8]. Tools capable of quantitating individual deficiencies and of documenting the effects of reconditioning would be useful. Evaluating the endurance of trunk extensor muscles seems to have greater discriminative validity than evaluation of maximal voluntary contractile force [9], [10], [11], [12], [13], [14].

In 1964, Hansen developed the first test for evaluating the isometric endurance of trunk extensor muscles and validated it in 168 healthy individuals and 90 patients who had had surgery for low back pain within the last 3–4 weeks [15]. In this test, the patient is in the prone position with the lower body fixed to the examining table and the upper body extending beyond the edge of the table. The test consists in holding the upper body horizontal as long as possible. In 1972, Troup et al. evaluated muscle fatigability by performing surface electromyography in patients during the test [16]. After a 1984 study by Biering-Sorensen [9] published in Spine, the test became known as the “Sorensen test”. Biering-Sorensen used the test together with several other evaluations in over 900 individuals and concluded that a shorter position-holding time during the Sorensen test predicted low back pain within the next year in males.

Section snippets

Methods

We conducted a Medline search for articles reporting the use of the Sorensen test to evaluate the back muscles. The keywords used for the search were “Sorensen test”, “back pain”, “muscle endurance”, “static endurance”, “muscle fatigue”, “function test”, “back extension”, and “trunk extensors”. In addition, the reference list of each article retrieved by the Medline search was examined for additional related articles.

Description of the Sorensen test

The patient lies on the examining table in the prone position with the upper edge of the iliac crests aligned with the edge of the table. The lower body is fixed to the table by three straps, located around the pelvis, knees, and ankles, respectively. With the arms folded across the chest, the patient is asked to isometrically maintain the upper body in a horizontal position (Fig. 1). The time during which the patient keeps the upper body straight and horizontal is recorded. In patients who

Predictive validity of the Sorensen test

Biering-Sorensen [9] reported that a position-holding time less than 176 s predicted low back pain during the next year in males, whereas a time greater than 198 s predicted absence of low back pain. Importantly, the test had no predictive validity in females. In a study by Luoto et al. [13], separating the participants into three groups based on position-holding times showed that a time less than 58 s was associated with a three-fold increase in the risk of low back pain, as compared to a time

Discriminative validity of the Sorensen test

In many studies, the position-holding time was significantly decreased in patients with chronic low back pain [9], [11], [15], [22], [24], [39], [56], [57]. This finding suggests that chronic low back pain may be associated with decreased isometric endurance of the trunk extensor muscles.

Biometric characteristics

In several studies, neither body weight [42], [58] nor mass moment of the trunk [10] influenced the position-holding time. Other studies, however, found a negative correlation between body weight and position-holding time [9], [19], [21], [27], [40]. The potential influence of age and stature remains debated [9], [10], [21], [27]. In contrast, there is general agreement that differences exist between males and females. With a few exceptions [21], [42], [59], studies found significantly longer

Reproducibility

The reproducibility of the Sorensen test has been evaluated, but the studies either included small numbers of individuals [10], [11], [30], [35], [60] or used the correlation coefficient r, which is not optimal for assessing test reproducibility [10], [21], [34], [36], [38], [57]. Investigations that relied on the intraclass coefficient of correlation (ICC) usually found that reproducibility was satisfactory (ICC > 0.75) [65] both in healthy individuals and in patients with low back pain.

Validity

Although Hansen [15] described the test as a tool for evaluating back strength, studies subsequently established that it assesses isometric muscle endurance. Furthermore, the muscle contractions elicited by the test were found to be no greater than 40–52% of the maximal voluntary contractile force [10], [25], [35], [45], [66], [67]. Similarly, the electromyographic activity of the spinal erector muscles rarely exceeded 40% of its maximal value [67], [68].

The Sorensen test has been

Sensitivity to change

The position-holding time has been reported to increase significantly after active rehabilitation therapy [38], [75]. A training program involving dynamic exercises performed on a Roman chair regularly over several weeks was followed by a significant increase in the position-holding time [71], although measurements obtained using a dedicated dynamometer showed no increase in back extensor muscle strength [32], [71].

Spinal loads induced by the Sorensen test

Callaghan et al. [76] estimated that the compression load imposed on the spine during the brief Sorensen test was 4000 N, which is slightly above the value recommended by the National Institute of Occupational Security and Health in 1981 [77].

Pain, including spinal pain, may cause the patient to discontinue the test [9], [24], [27], [28], [35]. However, no persistent adverse effects such as pain exacerbation have been reported. Simmonds et al. [22] found high within-session reproducibility and

Dynamometric measurements

Tests for evaluating isometric spinal muscle endurance using a dynamometer have been developed [11], [44], [78]. Jorgenssen et al. [11] reported that dynamometric measurements obtained at a fixed percentage of the voluntary maximal force (usually 50–60%) were superior over the Sorensen test with a 4-min maximum in several ways: the influence of anthropometric factors was smaller, reproducibility was better (with a correlation coefficient of 0.89 as compared to 0.82), discriminative validity was

Conclusions

The Sorensen test allows for a rapid, simple, and reproducible evaluation of the isometric endurance of the trunk extensor muscles. It discriminates between healthy individuals and patients with low back pain and may predict the occurrence of low back pain in the near future. Although the Sorensen test has been extensively studied, the better performance among females remains partly unexplained and the contribution of the hip extensor muscles is unknown. The absence of a single standardized

References (89)

S. Luoto et al.
Static back endurance and the risk of low-back pain
Clin. Biomech. (Bristol, Avon)
(1995)
J.K. Ng et al.
Reliability of electromyographic power spectral analysis of back muscle endurance in healthy subjects
Arch. Phys. Med. Rehabil.
(1996)
J.M. Mayer et al.
Electromyographic activity of the lumbar extensor muscles: effect of angle and hand position during Roman chair exercise
Arch. Phys. Med. Rehabil.
(1999)
P. Latikka et al.
Correlations of isokinetic and psychophysical back lift and static back extensor endurance tests in men
Clin. Biomech. (Bristol, Avon)
(1995)
A. Dedering et al.
Correlation between electromyographic spectral changes and subjective assessment of lumbar muscle fatigue in subjects without pain from the lower back
Clin. Biomech. (Bristol, Avon)
(1999)
A. Dedering
Roos af Hjelmsater M, Elfving B, Harms-Ringdahl K, Nemeth G. Between-days reliability of subjective and objective assessments of back extensor muscle fatigue in subjects without lower-back pain
J. Electromyogr. Kinesiol.
(2000)
J.M. Mayer et al.
Electromyographic activity of the trunk extensor muscles: effect of varying hip position and lumbar posture during Roman chair exercise
Arch. Phys. Med. Rehabil.
(2002)
M. Kankaanpaa et al.
Age, sex, and body mass index as determinants of back and hip extensor fatigue in the isometric Sorensen back endurance test
Arch. Phys. Med. Rehabil.
(1998)
G.A. Koumantakis et al.
Paraspinal muscle EMG fatigue testing with two methods in healthy volunteers. Reliability in the context of clinical applications
Clin. Biomech. (Bristol, Avon)
(2001)
S. Rashiq et al.
The effect of opioid analgesia on exercise test performance in chronic low back pain
Pain
(2003)

D.M. Novy et al.

Physical performance: differences in men and women with and without low back pain

Arch. Phys. Med. Rehabil.

(1999)

Y. Umezu et al.

Spectral electromyographic fatigue analysis of back muscles in healthy adult women compared with men

Arch. Phys. Med. Rehabil.

(1998)

S.M. McGill et al.

Endurance times for low back stabilization exercises: clinical targets for testing and training from a normal database

Arch. Phys. Med. Rehabil.

(1999)

J.P. Arokoski et al.

Back and hip extensor muscle function during therapeutic exercises

Arch. Phys. Med. Rehabil.

(1999)

T. Ito et al.

Lumbar trunk muscle endurance testing: an inexpensive alternative to a machine for evaluation

Arch. Phys. Med. Rehabil.

(1996)

O. Shirado et al.

Electromyographic analysis of four techniques for isometric trunk muscle exercises

Arch. Phys. Med. Rehabil.

(1995)

C.E. Moreau et al.

Isometric back extension endurance tests: a review of the literature

J. Manipulative Physiol. Ther.

(2001)

P. Leino et al.

Trunk muscle function and low back disorders: a ten-year follow-up study

J. Chronic Dis.

(1987)

B.C. Clark et al.

Electromyographic activity of the lumbar and hip extensors during dynamic trunk extension exercise

Arch. Phys. Med. Rehabil.

(2002)

M. Hillman et al.

Prevalence of low back pain in the community: implications for service provision in Bradford, UK

J. Epidemiol. Community Health

(1996)

C. Leboeuf-Yde et al.

How common is low back pain in the Nordic population? Data from a recent study on a middle-aged general Danish population and four surveys previously conducted in the Nordic countries

Spine

(1996)

A.C. Papageorgiou et al.

Estimating the prevalence of low back pain in the general population. Evidence from the South Manchester Back Pain Survey

Spine

(1995)

G.B. Andersson et al.

The intensity of work recovery in low back pain

Spine

(1983)

J.W. Frank et al.

Disability resulting from occupational low back pain. Part II: What do we know about secondary prevention? A review of the scientific evidence on prevention after disability begins

Spine

(1996)

T.G. Mayer et al.

Objective assessment of spine function following industrial injury. A prospective study with comparison group and one-year follow-up

Spine

(1985)

A.E. Bendix et al.

A prospective, randomized 5-year follow-up study of functional restoration in chronic low back pain patients

Eur. Spine J.

(1998)

M. Van Tulder et al.

Exercise therapy for low back pain: a systematic review within the framework of the Cochrane collaboration back review group

Spine

(2000)

F. Biering-Sorensen

Physical measurements as risk indicators for low-back trouble over a one-year period

Spine

(1984)

E. Hölmstrom et al.

Trunk muscle strength and back muscle endurance in construction workers with and without low back disorders

Scand. J. Rehabil. Med.

(1992)

K. Jorgensen

Human trunk extensor muscles physiology and ergonomics

Acta Physiol. Scand. Suppl.

(1997)

U.M. Kujala et al.

Physical loading and performance as predictors of back pain in healthy adults. A 5-year prospective study

Eur. J. Appl. Physiol. Occup. Physiol.

(1996)

T. Tsuboi et al.

Spectral analysis of electromyogram in lumbar muscles: fatigue induced endurance contraction

Eur. J. Appl. Physiol. Occup. Physiol.

(1994)

J.W. Hansen

Postoperative management in lumbar disc protrusions. I. Indications, method and results. II. Follow-up on a trained and an untrained group of patients

Acta Orthop. Scand.

(1964)

J.D. Troup et al.

Changes in the waveform of the electromyogram during fatiguing activity in the muscles of the spine and hips: the analysis of postural stress

Electromyogr. Clin. Neurophysiol.

(1972)

A.F. Mannion et al.

The influence of muscle fiber size and type distribution on electromyographic measures of back muscle fatigability

Spine

(1998)

L.E. Gibbons et al.

Determinants of isokinetic and psychophysical lifting strength and static back muscle endurance: a study of male monozygotic twins

Spine

(1997)

E. Suter et al.

Back muscle fatigability is associated with knee extensor inhibition in subjects with low back pain

Spine

(2001)

H. Alaranta et al.

Non-dynamometric trunk performance tests: reliability and normative data

Scand. J. Rehabil. Med.

(1994)

M.J. Simmonds et al.

Psychometric characteristics and clinical usefulness of physical performance tests in patients with low back pain

Spine

(1998)

J. Latimer et al.

The reliability and validity of the Biering-Sorensen test in asymptomatic subjects and subjects reporting current or previous nonspecific low back pain

Spine

(1999)

J.K. Ng et al.

Electromyographic amplitude and frequency changes in the iliocostalis lumborum and multifidus muscles during a trunk holding test

Phys. Ther.

(1997)

R.G. Cooper et al.

Increased central drive during fatiguing contractions of the paraspinal muscles in patients with chronic low back pain

Spine

(1993)

J. Moreland et al.

Interrater reliability of six tests of trunk muscle function and endurance

J. Orthop. Sports Phys. Ther.

(1997)

A. Keller et al.

Reliability of the isokinetic trunk extensor test, Biering-Sorensen test, and Astrand bicycle test: assessment of intraclass correlation coefficient and critical difference in patients with chronic low back pain and healthy individuals

Spine

(2001)

Cited by (207)

Efficacy of kinesio tape added to lumbar stabilization exercises on adult patients with mechanical low back pain: A randomized, single-blind clinical trial
2024, Journal of Bodywork and Movement Therapies
Lumbar stabilization exercises (LSEs) are beneficial for chronic mechanical low back pain (CMLBP). However, further research focusing on intervention combinations is recommended. This study examined the effect of kinesio tape (KT) with LSEs on CMLBP adult patients.
A randomized blinded clinical trial was conducted. Fifty CMLBP patients of both genders were assigned into one of two groups and received 8 weeks of treatment: group A (control): LSEs only, and group B (experimental): KT with LSEs. The primary outcome was back disability, measured by the Oswestry disability index. Secondary outcomes included pain intensity, trunk extensor endurance, and sagittal spinal alignment, as indicated by the visual analog scale, Sorensen-test, and C7–S1 sagittal vertical axis, respectively. The reported data was analyzed by a two-way MANOVA using an intention-to-treat procedure.
Multivariate tests indicate statistically significant effects for group (F = 4.42, p = 0.005, partial η2 = 0.148), time (F = 219.55, p < 0.001, partial η2 = 0.904), and group-by-time interaction (F = 3.21, p = 0.01, partial η2 = 0.149). Univariate comparisons between groups revealed significant reductions in the experimental group regarding disability (p = 0.029, partial η2 = 0.049) and pain (p = 0.001, partial η2 = 0.102) without a significant difference in the Sorensen test (p = 0.281) or C7–S1 SVA (p = 0.491) results. All within-group comparisons were statistically significant (p < 0.001).
The combination of KT and LSEs is an effective CMLBP treatment option. Although patients in both groups displayed significant changes in all outcomes, the combined interventions induced more significant reductions in back disability and pain intensity.
Understanding the Biering-Sørensen test: Contributors to extensor endurance in young adults with and without a history of low back pain
2024, Journal of Electromyography and Kinesiology
The Biering-Sørensen test is commonly used to assess paraspinal muscle endurance. Research using a single repetition of the test has provided conflicting evidence for the contribution of impaired paraspinal muscle endurance to low back pain (LBP). This study investigated how Sørensen test duration, muscle activation, and muscle fatigability are affected by multiple repetitions of the test and determined predictors of Sørensen test duration in young adults with and without a history of LBP. Sixty-four young individuals performed three repetitions of the Sørensen test. Amplitude of activation and median frequency slope (fatigability) were calculated for the lumbar and thoracic paraspinals and hamstrings. Duration of the test was significantly less for the 3rd repetition in individuals with LBP. In individuals without LBP, test duration was predicted by fatigability of the lumbar paraspinals. In individuals with LBP, Sørensen test duration was predicted by fatigability of the hamstrings and amplitude of activation of the thoracic and lumbar paraspinals. Our findings demonstrate that it is necessary to amplify the difficulty of the Sørensen test to reveal impairments in young, active adults with LBP. Training programs aiming to improve lumbar paraspinal performance should monitor performance of other synergist muscles during endurance exercise.
Spine-specific sarcopenia: distinguishing paraspinal muscle atrophy from generalized sarcopenia
2024, Spine Journal
Atrophy of the paraspinal musculature (PM) as well as generalized sarcopenia are increasingly reported as important parameters for clinical outcomes in the field of spine surgery. Despite growing awareness and potential similarities between both conditions, the relationship between “generalized” and “spine-specific” sarcopenia is unclear.
To investigate the association between generalized and spine-specific sarcopenia.
Retrospective cross-sectional study.
Patients undergoing lumbar spinal fusion surgery for degenerative spinal pathologies.
Generalized sarcopenia was evaluated with the short physical performance battery (SPPB), grip strength, and the psoas index, while spine-specific sarcopenia was evaluated by measuring fatty infiltration (FI) of the PM.
We used custom software written in MATLAB® to calculate the FI of the PM. The correlation between FI of the PM and assessments of generalized sarcopenia was calculated using Spearman's rank correlation coefficient (rho). The strength of the correlation was evaluated according to established cut-offs: negligible: 0–0.3, low: 0.3–0.5, moderate: 0.5–0.7, high: 0.7–0.9, and very high≥0.9. In a Receiver Operating Characteristics (ROC) analysis, the Area Under the Curve (AUC) of sarcopenia assessments to predict severe multifidus atrophy (FI≥50%) was calculated. In a secondary analysis, factors associated with severe multifidus atrophy in non-sarcopenic patients were analyzed.
A total of 125 (43% female) patients, with a median age of 63 (IQR 55–73) were included. The most common surgical indication was lumbar spinal stenosis (79.5%). The median FI of the multifidus was 45.5% (IQR 35.6–55.2). Grip strength demonstrated the highest correlation with FI of the multifidus and erector spinae (rho=-0.43 and -0.32, p<.001); the other correlations were significant (p<.05) but lower in strength. In the AUC analysis, the AUC was 0.61 for the SPPB, 0.71 for grip strength, and 0.72 for the psoas index. The latter two were worse in female patients, with an AUC of 0.48 and 0.49. Facet joint arthropathy (OR: 1.26, 95% CI: 1.11–1.47, p=.001) and foraminal stenosis (OR: 1.54, 95% CI: 1.10–2.23, p=.015) were independently associated with severe multifidus atrophy in our secondary analysis.
Our study demonstrates a low correlation between generalized and spine-specific sarcopenia. These findings highlight the risk of misdiagnosis when relying on screening tools for general sarcopenia and suggest that general and spine-specific sarcopenia may have distinct etiologies.
Effect of aerobic exercises on patients with chronic mechanical low back pain: A randomized controlled clinical trial
2024, Journal of Bodywork and Movement Therapies
Chronic mechanical low back pain (CMLBP) is one of the most prevalent and costly disorders. Determining its most effective treatment approach is a priority for researchers.
To examine the effects of including aerobic exercise within a conventional therapy regimen for young adults with CMLBP.
Fifty CMLBP patients (22 males and 28 females) were randomly and equally assigned to one of two groups to receive the prescribed treatment for 8 weeks. The control group received the traditional program only (infrared, ultrasound, burst TENS, and exercises); for the experimental group, an aerobic training program using a stationary bicycle was added. Back pain intensity was the primary outcome. Secondary outcomes included the Oswestry disability index, back extensor endurance measured by the Sorensen test, and physical performance indicated by the back performance scale and the 6-min walk test. A Two-way MANOVA was used for data analysis.
Multivariate tests revealed statistically significant effects of group (p = 0.002, partial η2 = 0.182), time (p < 0.001, partial η2 = 0.928), and group-by-time interaction (p = 0.01, partial η2 = 0.149). Univariate group-by-time interactions were significant for back disability (p = 0.043), extensor endurance (p = 0.023) and results of the 6-min walk test (p = 0.023) showing greater improvement in the experimental group. However, back pain intensity and the back performance scale revealed no significant group-by-time interactions. Within-group comparisons were significant for all measured variables in both groups (p < 0.001).
Although a traditional program of infrared, ultrasound, TENS, and exercises is beneficial for CMLBP treatment, adding aerobic exercises to the program leads to more beneficial outcomes.
Fatigue task-dependent effect on spatial distribution of lumbar muscles activity
2023, Journal of Electromyography and Kinesiology
This study aims to identify how spatial distribution of lumbar muscle activity is modulated by different fatigue tasks. Twenty healthy adults performed two different isometric trunk extension endurance tasks (the modified Sorensen test and the inverted modified Sorensen test) until exhaustion. During these tasks, bilateral superficial lumbar muscle activity was recorded using high-density electromyography. The spatial distribution of activation within these muscles was obtained using the centroid coordinates in the medio-lateral and cranio-caudal directions. The effects of task and endurance time (left and right sides) were investigated using repeated measures ANOVA. Results revealed a significant lateral shift of the centroid throughout the fatigue tasks on both sides and no difference between tasks. Significant task × time interaction effects were found for the cranio-caudal direction on both sides showing a significantly more caudal location of the centroid in the modified Sorensen test compared to the inverted test at the beginning of the tasks. Our findings suggest that spatial distribution of lumbar muscle activity is task-dependent in a pre-fatigue stage while an alternative but similar muscle recruitment strategy is used in both tasks to maintain performance in the later stages of muscle fatigue.
Linear spectrum and non-linear complexity features of lumbar muscle surface electromyography between people with and without non-specific chronic low back pain during Biering-Sorensen test
2023, Journal of Electromyography and Kinesiology
This study aimed to investigate the electromyographic parameters of lumbar muscles during the Biering-Sorensen test (BST) in people with and without non-specific chronic low back pain (NCLBP).
Thirteen healthy controls and thirteen NCLBP patients participated in the current study, where they performed the 90s-BST, while the surface electromyography (sEMG) was recorded from the erector spinae (ES) at L1 and L3 level and lumbar multifidus (LM) at L5 level, bilaterally. Spectral and nonlinear analyses were applied by calculating mean power frequency (MPF), fractal dimension (FD) and the percentage of determinism (%DET) in the 10-second non-overlapping time-windows and EMG-EMG coherence during the first half and second half of the BST. Also, the slopes of the linear fitting curves of MPF, FD and %DET were calculated.
NCLBP group had significantly lower rates of changes in MPF, FD and %DET compared to asymptomatic controls in the ES(L3) and LM. Coherence in left–right LM and in the right ES-LM increased significantly in the gamma band in the Control group with no increase in the NCLBP group.
Our findings indicated that compared to people with NCLBP, the sEMG signals of lumbar muscles of people without NCLBP were more regular and less complex during the 90s-BST.

View all citing articles on Scopus

View full text

ReviewSpinal muscle evaluation using the Sorensen test: a critical appraisal of the literature

Abstract

Introduction

Section snippets

Methods

Description of the Sorensen test

Predictive validity of the Sorensen test

Discriminative validity of the Sorensen test

Biometric characteristics

Reproducibility

Validity

Sensitivity to change

Spinal loads induced by the Sorensen test

Dynamometric measurements

Conclusions

Clin. Biomech. (Bristol, Avon)

Arch. Phys. Med. Rehabil.

Arch. Phys. Med. Rehabil.

Clin. Biomech. (Bristol, Avon)

Clin. Biomech. (Bristol, Avon)

J. Electromyogr. Kinesiol.

Arch. Phys. Med. Rehabil.

Arch. Phys. Med. Rehabil.

Clin. Biomech. (Bristol, Avon)

Pain

Arch. Phys. Med. Rehabil.

Arch. Phys. Med. Rehabil.

Arch. Phys. Med. Rehabil.

Arch. Phys. Med. Rehabil.

Arch. Phys. Med. Rehabil.

Arch. Phys. Med. Rehabil.

J. Manipulative Physiol. Ther.

J. Chronic Dis.

Arch. Phys. Med. Rehabil.

Prevalence of low back pain in the community: implications for service provision in Bradford, UK

J. Epidemiol. Community Health

How common is low back pain in the Nordic population? Data from a recent study on a middle-aged general Danish population and four surveys previously conducted in the Nordic countries

Spine

Estimating the prevalence of low back pain in the general population. Evidence from the South Manchester Back Pain Survey

Spine

The intensity of work recovery in low back pain

Spine

Disability resulting from occupational low back pain. Part II: What do we know about secondary prevention? A review of the scientific evidence on prevention after disability begins

Spine

Objective assessment of spine function following industrial injury. A prospective study with comparison group and one-year follow-up

Spine

A prospective, randomized 5-year follow-up study of functional restoration in chronic low back pain patients

Eur. Spine J.

Exercise therapy for low back pain: a systematic review within the framework of the Cochrane collaboration back review group

Spine

Physical measurements as risk indicators for low-back trouble over a one-year period

Spine

Trunk muscle strength and back muscle endurance in construction workers with and without low back disorders

Scand. J. Rehabil. Med.

Human trunk extensor muscles physiology and ergonomics

Acta Physiol. Scand. Suppl.

Physical loading and performance as predictors of back pain in healthy adults. A 5-year prospective study

Eur. J. Appl. Physiol. Occup. Physiol.

Spectral analysis of electromyogram in lumbar muscles: fatigue induced endurance contraction

Eur. J. Appl. Physiol. Occup. Physiol.

Postoperative management in lumbar disc protrusions. I. Indications, method and results. II. Follow-up on a trained and an untrained group of patients

Acta Orthop. Scand.

Changes in the waveform of the electromyogram during fatiguing activity in the muscles of the spine and hips: the analysis of postural stress

Electromyogr. Clin. Neurophysiol.

The influence of muscle fiber size and type distribution on electromyographic measures of back muscle fatigability

Spine

Determinants of isokinetic and psychophysical lifting strength and static back muscle endurance: a study of male monozygotic twins

Spine

Back muscle fatigability is associated with knee extensor inhibition in subjects with low back pain

Spine

Non-dynamometric trunk performance tests: reliability and normative data

Scand. J. Rehabil. Med.

Psychometric characteristics and clinical usefulness of physical performance tests in patients with low back pain

Spine

The reliability and validity of the Biering-Sorensen test in asymptomatic subjects and subjects reporting current or previous nonspecific low back pain

Spine

Electromyographic amplitude and frequency changes in the iliocostalis lumborum and multifidus muscles during a trunk holding test

Phys. Ther.

Increased central drive during fatiguing contractions of the paraspinal muscles in patients with chronic low back pain

Spine

Review
Spinal muscle evaluation using the Sorensen test: a critical appraisal of the literature