Evaluation of the flexion relaxation phenomenon of the trunk muscles in sitting

Effect of the Law Enforcement Duty Belt on Muscle Activation during Hip Hinging Movements in Young, Healthy Adults

Sixty percent of all law enforcement officers (LEOs) experience low back pain (LBP), with the LEO duty belt (LEO_DB) commonly reported to be a contributing factor. The primary purpose of the study was to investigate the LEODB's effect on muscular activity and compare it to a tactical vest, which is a commonly used alternative to an LEO_DB. In total, 24 participants (13 male, 11 female; mass, 73.0 ± 11.1 kg; height, 169.0 ± 10.0 cm; age, 24.0 ± 5.8 years) completed a progressive series of hip hinge tasks in a single testing session. All participants completed four conditions (no belt, leather belt, nylon belt, and weight VEST) in a randomized order. Surface electromyography (sEMG) sensors were placed bilaterally on the rectus abdominus, multifidus, biceps femoris, and rectus femoris. Across all tasks, no significant effects of load on muscle activity were found for any of the muscles. Participants rated the VEST condition as more comfortable (p < 0.05) and less restrictive (p < 0.05) than either LEODB. The findings suggest an LEO_DB does not alter muscle activity during bodyweight hip hinging or lifting objects from the ground. Future research should examine whether changes in muscle activity occur with durations of LEO_DB wear more similar to an actual work shift duration for LEOs (≥8 h).

The influence of sedentary behaviour on lumbar-pelvic kinematics during squatting and forward bending among physically active students

Prolonged sitting may involve several mechanisms that make it a risk factor for low back pain. The aim of this study was to investigate lumbar-pelvic kinematics and multifidus muscle (MF) activity during squatting and forward bending in relation to the sedentary behaviour of physically active students. Sixty-three students were divided into two groups according to the time spent in a sitting position during the day: 'high' (>7 h/day); 'low' (≤7 h/day). Lumbar-pelvic ratios, ranges of motion, angular velocities, and MF flexion-relaxation phenomenon were investigated. Data were obtained using the optical motion analysis system, and surface electromyography. The results indicated that lumbar-pelvic ratios during both tasks and velocity of lumbar spine during squatting were significantly greater in the 'high' than in the 'low' sitting group. Muscle activity showed no differences between groups. Prolonged sitting can be considered a factor that slightly, but statistically significantly influences the lumbar-pelvic kinematics in physically active people.Practitioner summary: Lumbar-pelvic kinematics can be altered by prolonged sitting in physically active students. Lumbar-pelvic ratios during squatting and forward bending and lumbar spine velocity during squatting were significantly greater in the 'high' than in the 'low' sitting group. Sedentary behaviour should be considered during an assessment of movement patterns.Abbreviations: BMI: body mass index; ERR: extension-relaxation ratio; FRP: flexion-relaxation phenomenon; FRR: flexion-relaxation ratio; IPAQ: International Physical Activity Questionnaire; LBP: low back pain; METs: metabolic equivalent of tasks; MF: multifidus muscle; PA: physical activity; ROM: range of motion; sEMG: surface electromyography.

The occurrence of flexion-relaxation phenomenon in elite cyclists during trunk forward bending

Flexion-relaxation phenomenon (FRP) is a well-known phenomenon in spinal extensor muscles. According to the literature, prolonged flexed posture leads to creep phenomenon and affects the active and passive neuromuscular control of the spinal column. The purpose of this study was to investigate FRP occurrence in elite cyclists that prolonged flexion posture is an integral part of their professional life. Their muscles' contraction pattern during forward bending was also compared. Electromyography (EMG) was recorded during flexion and extension from standing position in thoracic erector spinae (TES), lumbar erector spinae (LES) and gluteus maximus (Gluteus max) in 15 healthy male elite cyclists. In addition, the kinematic data related to the trunk angles were simultaneously recorded by a motion analysis system. Two-way ANOVA was used to assess the effects of muscle group and direction of movement on maximum amplitude of EMG activity. Among 15 cyclists, FRP was detectable in 60%, 87% and 73% of the participants in TES, LES and Gluteus max, respectively, and happened between 74% and 82% of the trunk flexion. There was no statistically significant difference in onset and offset of muscles FRP. Despite prolong hyper kyphotic posture, FRP was identifiable in TES, LES and Gluteus max muscles of elite cyclists.

Local dynamic stability of the trunk after prolonged seating with axial load

Fatigue from prolonged seating with an axial load on the trunk may impair neuromuscular control and spine stability which may elevate risk of low back pain (LBP) for dynamic tasks following seating. The objective of this study was to assess local dynamic trunk stability using the maximum Lyapunov exponent (λ_MAX) with corresponding coactivation patterns to understand possible effects from prolonged seating. An increase in λ_MAX would indicate decreased stability. Twenty participants (10 male, 10 female) performed a controlled, cyclic sagittal flexion task at 40 cycles per minute before and after three hours of seating in a simulated helicopter-seating environment with a weighted vest. A statistically significant decrease was seen in λ_MAX (bits/s) (Pre-Test = 0.654 ± 0.172; Post-Test = 0.829 ± 0.268, p = 0.002), trunk cumulative coactivation index (unitless/s) (Pre-Test = 1.71 ± 0.97; Post-Test = 1.59 ± 0.96, p = 0.0095), and abdominal activation (normalized) (Pre-Test = 0.46 ± 0.17, Post-Test = 0.41 ± 0.18, p = 0.0146) post-seating exposure. Trunk extension was reduced (∼4°, p = 0.0004) during the post-seating cyclic test with slight corresponding increases in flexion. This study provides evidence of potential effects of fatigue from prolonged seating to neuromuscular control, which may have implications for occupations requiring highly dynamic tasks after prolonged seated postures. Future studies would repeat the tests with dynamic environments (i.e., vibration), test the cyclic flexion protocols with different seating interventions, and continue to test the approach to develop a tool to assess back impairment or intervention effectiveness.

The influence of experimental low back pain on neural networks involved in the control of lumbar erector spinae muscles

INTRODUCTION

Low back pain (LBP) often modifies spine motor control, but the neural origin of these motor control changes remains largely unexplored. This study aimed to determine the impact of experimental low back pain on the excitability of cortical, subcortical, and spinal networks involved in the control of back muscles.

METHOD

Thirty healthy subjects were recruited and allocated to Pain (capsaicin and heat) or Control (heat) groups. Corticospinal excitability (motor-evoked potential-MEP) and intracortical networks were assessed by single- and paired-pulse transcranial magnetic stimulation, respectively. Electrical vestibular stimulation was applied to assess vestibulospinal excitability (vestibular MEP-VMEP), and the stretch reflex for excitability of the spinal or supraspinal loop (R1 and R2, respectively). Evoked back motor responses were measured before, during and after pain induction. Nonparametric rank-based ANOVA determined if pain modulated motor neural networks.

RESULTS

A decrease of R1 amplitude was present after the pain disappearance (p=0.01) whereas an increase was observed in the control group (p=0.03) compared to the R1 amplitude measured at pre-pain and pre-heat period, respectively (Group x Time interaction - p<0.001). No difference in MEP and VMEP amplitude was present during and after pain (p>0.05).

CONCLUSION

During experimental LBP, no change in cortical, subcortical, or spinal networks was observed. After pain disappearance, the reduction of the R1 amplitude without modification of MEP and VMEP amplitude suggest a reduction in spinal excitability potentially combined with an increase in descending drives. The absence of effect during pain needs to be further explored.

Sagittal imbalance of the spine is associated with poor sitting posture among primary and secondary school students in China: a cross-sectional study

Background

Long-term poor posture may affect the morphological development of the spine. However, there is no definite answer as to how writing posture affects students’ spine. This study attempted to compare the sagittal curvature of the spine between sitting and standing postures in adolescents to reveal the variation rule of spinal sagittal curvature of students with learning posture, and to discover the key factors that may affect students’ spinal health.

Methods

1138 participants (male, 604; female, 534; age range, 6–18 years) from three schools in Tianjin, China, including 570 primary school students and 568 secondary school students. This study used SpineScan and PA200 Station Posture Assessment System to assess the sagittal curvature of the spine for three postures: sitting on a chair in upright position, seated at a desk while reading/writing, and standing in natural relaxed position. Analyze the difference between spine angle of the three postures and the correlation between the sagittal plane angle of the spine and body posture.

Results

The mean sagittal angle of the spine changed when the participants were in reading/writing position compared to standing position, with the lumbar lordosis angle significantly decreased (p < 0.05) and the thoracic kyphosis angle significantly increased (p < 0.05). The TKA and LLA angles were abnormal in 33 and 52% of students in reading/writing posture respectively. There was a significant correlation between sitting posture and standing spinal Angle and were positively correlated with the height of the teenager (p < 0.05). By contrast, a higher percentage of TKA and LLA subjects in the standard reading/writing posture reference range maintained normal spinal shape while standing.

Conclusions

The angle of thoracic kyphosis significantly increased from standing posture to upright sitting, reading/writing posture, while lumbar lordosis significantly decreased or even disappeared. There was a significant correlation between sagittal angle of spine in different postures. The poor sitting posture associated with sagittal angle abnormalities impact the shape of the spine such that sagittal imbalance was also observed when students in natural standing posture. Height is an important factor affecting the sitting spine shape of students.

Effects of Prolonged Sitting with Slumped Posture on Trunk Muscular Fatigue in Adolescents with and without Chronic Lower Back Pain

Background and Objectives: This study investigated the effects of prolonged sitting on trunk muscular fatigue and discomfort in participants with and without chronic lower back pain (LBP). Material and Methods: This study included 15 patients with LBP and 15 healthy controls. All participants were instructed to sit on a height-adjustable chair with their knee and hip joints bent at 90° for 30 min, in slumped sitting postures. Surface electromyography was used to assess the median frequency of the internal obliques (IO)/transversus abdominis (TrA) and multifidus (MF) muscles. Perceived discomfort was measured using a Borg category ratio-scale. Median frequency of the trunk muscles and perceived discomfort after 30 min of sitting were compared with baseline. Result: There were no significant differences within the group and between both groups in the median frequency of bilateral IO and MF muscles. The LBP group showed significantly greater perceived discomfort after prolonged sitting, as compared to the control group. Conclusions: Prolonged sitting with slumped posture could increase the risk of experiencing lower back discomfort.

Preoperative and Postoperative Sitting Radiographs for Adult Spinal Deformity Surgery: Upper Instrumented Vertebra Selection Using Sitting C2 Plumb Line Distance to Prevent Proximal Junctional Kyphosis

STUDY DESIGN

Case-control study from a continuous series.

OBJECTIVES

To study the impact of perioperative sitting radiographs in adult spinal deformity (ASD) patients and determine whether proximal junctional kyphosis (PJK) can be prevented using preoperative sitting radiograph.

SUMMARY OF BACKGROUND DATA

Radiographic analysis of ASD comprises standing whole-spine radiography which cannot evaluate the relaxed posture without head-to-foot compensation.

METHODS

Preoperative and postoperative whole-spine standing and sitting radiographs and proximal mechanical complications in surgically treated spinal disorders with a minimum of 1-year follow-up were studied. Whole-spinal alignment was defined by cervical lordosis (CL), sagittal vertical axis (SVA), T1 slope (T1S), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and level of kyphotic apex (KA). Proximal mechanical complication was described as a PJK (proximal junctional angle >20°) or reoperation due to proximal junctional failure.

RESULTS

Surgically treated 113 patients were prospectively investigated. Patients were divided into either the ASD (thoracic to ilium posterior corrective fusion), or non-ASD groups. In the ASD group, 10 patients had postoperative PJK, and three revision surgeries were carried out due to PJF with neurological deficit. Comparing standing with sitting positions, CL, TK, and PT became larger, SVA became frontal, LL and SS became smaller, and KA became caudal particularly in the ASD group. Logistic regression analysis demonstrated that the most influenced plumb line for PJK was the upper instrumented vertebra (UIV) to C2 plumb line distance, with a cutoff value of 115 mm for predicting PJK.

CONCLUSION

Our findings highlight the usefulness of sitting spinal alignment evaluation, particularly in ASD patients, with maximum effort of thoracic spine and lower extremity compensation at standing. Mechanical complications such as PJK could be predicted using the distance from the planned UIV to the C2 plumb line in preoperative sitting radiographs.

LEVEL OF EVIDENCE

3.

Effects of varying the rest period on the onset angle of lumbar flexion-relaxation in simulated sheep shearing: a preliminary study

Wool harvesting remains an important industry in Australia, but its workers suffer from extreme rates of injury, in particular, the lower back injuries. Reducing injuries in sheep shearing could be as simple as extending shearer rest periods between sheep, but the effect of this has not previously been studied. The lumbar flexion-relaxation phenomenon is present in sheep shearing and the onset angle of this phenomenon can provide insight into lower back injury risk. The increase in the onset angle of lumbar flexion-relaxation over several work-rest periods for a simulated sheep shearing task is studied. The rate of increase in the onset angle of lumbar flexion-relaxation was higher when shorter breaks were taken for all participants at least unilaterally, indicating that longer rest breaks could reduce back injury risk. Due to the constraints of the sheep shearing occupation, this type of intervention is better suited to learner and novice shearers. Assistive robotic devices would be more suited to reduce injuries in expert shearers, and some insight is provided for the application of these within sheep shearing. Further study of this phenomenon in sheep shearing could provide additional insight to developing an assistive device that could reduce injury.

Back Muscle Function in Older Women With Age-Related Hyperkyphosis: A Comparative Study

OBJECTIVE

The purpose of this study was to compare static maximal back extensor muscle force, endurance, and characteristics of flexion relaxation phenomenon (FRP) in older women with and without age-related hyperkyphosis.

METHODS

Maximum back extensor force and endurance measured in a sitting position with a designed load cell setup; appearance, onset, and offset angles of FRP; and extension relaxation ratio (ERR) during a dynamic flexion-extension task were compared between 24 older women with hyperkyphosis (thoracic kyphosis angle ≥50°), mean age 65 ± 4.4 years, and 24 older women without hyperkyphosis (thoracic kyphosis angle ≪50°), mean age 63 ± 4.3 years. Variables of force, endurance, angles of FRP, and ERR were analyzed using an independent sample t test. A χ² test was used to identify differences between groups in FRP appearance.

RESULTS

Static back extensor force and endurance were significantly lower among those with versus those without hyperkyphosis (P ≪ .001). Although the 2 groups did not differ in FRP appearance and ERR in the superficial erector spinal muscles (P ≫ .05), FRP in the hyperkyphosis group started sooner and ended later than in the group without hyperkyphosis (P ≪ .05).

CONCLUSION

Our study indicates that women with age-related hyperkyphosis had decreased static maximal force and endurance of the back extensor muscles and prolonged myoelectrical silence of the superficial erector spinal muscles. Reduced endurance of the superficial erector spinal muscles may trigger early onset of FRP and prolonged relaxation of these muscles.

Effects of myofascial release in erector spinae myoelectric activity and lumbar spine kinematics in non-specific chronic low back pain: Randomized controlled trial

BACKGROUND

Flexion-relaxation response of the lumbar erector spinae has been previously studied after different interventions such as exercise programs or spinal manipulation, in subjects with chronic low back pain. The objective of the study was to investigate the effects of an isolated myofascial release protocol on erector spinae myoelectric activity and lumbar spine kinematics in chronic low back pain.

METHODS

Thirty-six participants, with nonspecific chronic low back pain, were randomized to myofascial release group (n = 18) receiving four sessions of myofascial treatment, each lasting 40 min, and to control group (n = 18) receiving a sham myofascial release. Electromyographic and kinematic variables as well as pain and disability questionnaires were analyzed.

FINDINGS

There was a bilateral reduction of the flexion relaxation ratio in individuals receiving myofascial release and who did not show myoelectric silence at baseline (right difference M = 0.34, 95% CI [0.16, 0.33], p ≤ .05 and left difference M = 0.45, 95% CI [0.16, 0.73], p ≤ .05). There was also a significant reduction in pain in the myofascial release group (difference M = -9.1, 95% CI [-16.3, -1.8], p ≤ .05) and disability (difference M = -5.6, 95% CI [-9.1, -2.1], p ≤ .05), compared with control group. No significant differences between groups were found for the kinematic variables.

INTERPRETATION

The myofascial release protocol contributed to the normalization of the flexion- relaxation response in individuals who did not show myoelectric silence before the intervention, and also showed a significant reduction in pain and disability compared with the sham group.

Do different sitting postures affect spinal biomechanics of asymptomatic individuals?

BACKGROUND

Static sitting is thought to be related to low back pain. Of various common seated postures, slouched sitting has been suggested to cause viscoelastic creep. This, in turn, may compromise trunk muscle activity and proprioception, and heightening the risk of low back pain. To date, no research has evaluated immediate and short-term effects of brief exposures to different sitting postures on spinal biomechanics and trunk proprioception.

RESEARCH QUESTION

This study aimed to compare the impacts of 20 min of static slouched, upright and supported sitting with a backrest on trunk range of motion, muscle activity, and proprioception immediately after and 30 min after the sitting tasks.

METHODS

Thirty-seven adults were randomly assigned to the three sitting posture groups. Surface electromyography of six trunk muscles during maximum voluntary contractions were measured at baseline for normalization. Pain intensity, lumbar range of motion, and proprioceptive postural control strategy were assessed at baseline, 20 min (immediately post-test) and at 50 min (recovery). Trunk muscle activity during sitting was continuously monitored by surface electromyography.

RESULTS

While the slouched sitting group demonstrated the lowest bilateral obliquus internus/transversus abdominis activity as compared to other sitting postures (F = 4.87, p < 0.05), no significant temporal changes in pain intensity, lumbar range of motion nor proprioceptive strategy were noted in any of the groups.

SIGNIFICANCE

Sitting for 20 min of duration appears to have no adverse effects on symptoms or spinal biomechanics regardless of the posture adopted. Future research should determine if there is a point at which does slouched sitting cause significant changes in pain/spinal biomechanics in people both with and without low back pain.

Flexion-Relaxation Phenomenon in Children and Adolescents With and Without Nonspecific Chronic Low Back Pain: An Electromyographic and Kinematic Cross-Sectional Comparative Study

STUDY DESIGN

A cross-sectional comparative study.

OBJECTIVE

This study aimed to investigate the flexion-relaxation phenomenon (FRP), in standing trunk flexion and slumped sitting tasks, by comparing children and adolescents suffering from nonspecific chronic low back pain (NSCLBP) with controls (CTRL).

SUMMARY OF BACKGROUND DATA

The absence of the FRP can accurately discriminate adults with NSCLBP from those without during standing trunk flexion and slumped sitting tasks. Even if the FRP has been extensively studied in adults with NSCLBP, only one study has evaluated the FRP in adolescents, during a slumped sitting task, and this suggested that the FRP was also present in adolescents with NSCLBP.

METHODS

Thirty-seven children and adolescents with NSCLBP and 23 CTRL performed standing trunk flexion and slumped sitting tasks. All participants were equipped with surface electromyography (EMG) electrodes on the erector spinae longissimus (ESL) and multifidus (M) muscles and reflective markers on the spinous processes of C7, L1, and S1. Global (C7-S1), thoracic (C7-L1), and lumbar (L1-S1) trunk flexion absolute angle were measured. The FRP was reported using visual inspection and a flexion-relaxation ratio (FRR). A self-reference threshold was used to identify the time of FRP onset. Repeated-measures analysis of variance (ANOVA) was used to determine the main and interaction effects of task, group and muscle on FRR, and the relative maximal angle at FRP onset of the global trunk (C7-S1).

RESULTS

Results showed three main findings: (1) the FRP's low sensitivity in discriminating between NSCLBP and CTRL participants in groups, tasks, or muscles; (2) similar observed maximal flexion angles in both groups during flexion tasks; and (3) similar observed relative maximal global trunk flexion angles at FRP onset in groups, tasks, and muscles.

CONCLUSION

These results are not consistent with the literature on adults and could lead to modified therapeutic management of NSCLBP in children and adolescents.

LEVEL OF EVIDENCE

3.

Have Studies that Measure Lumbar Kinematics and Muscle Activity Concurrently during Sagittal Bending Improved Understanding of Spinal Stability and Sub-System Interactions? A Systematic Review

In order to improve understanding of the complex interactions between spinal sub-systems (i.e., the passive (ligaments, discs, fascia and bones), the active (muscles and tendons) and the neural control systems), it is necessary to take a dynamic approach that incorporates the measurement of multiple systems concurrently. There are currently no reviews of studies that have investigated dynamic sagittal bending movements using a combination of electromyography (EMG) and lumbar kinematic measurements. As such it is not clear how understanding of spinal stability concepts has advanced with regards to this functional movement of the spine. The primary aim of this review was therefore to evaluate how such studies have contributed to improved understanding of lumbar spinal stability mechanisms. PubMed and Cochrane databases were searched using combinations of the keywords related to spinal stability and sagittal bending tasks, using strict inclusion and exclusion criteria and adhering to PRISMA guidelines. Whilst examples of the interactions between the passive and active sub-systems were shown, typically small sample sizes meant that results were not generalizable. The majority of studies used regional kinematic measurements, and whilst this was appropriate in terms of individual study aims, the studies could not provide insight into sub-system interaction at the level of the spinal motion segment. In addition, the heterogeneity in methodologies made comparison between studies difficult. The review suggests that since Panjabi’s seminal spinal control papers, only limited advancement in the understanding of these theories has been provided by the studies under review, particularly at an inter-segmental level. This lack of progression indicates a requirement for new research approaches that incorporate multiple system measurements at a motion segment level.

[Low back pain perception from the prolonged use of a dynamic seat in sitting posture]

Objective To determine whether a tilting system located in the seat of a chair allows for performing voluntary macro-repositioning movements of the pelvis in order to reduce the perception of pain after a prolonged period in the sitting posture. Methods Eight women participated in the experiment. They were asked to sit on the chair with the tilting system and the chair without the tilting system for sixty minutes on two different days but carried out at the same time of day. Discomfort was assessed with the visual analogic scale. Results people used the tilting system to do postural changes of macro-repositioning. However, these movements were less than the movements done with the body, not using the system. Moreover, discomfort perception was the same for each chair. This might be due to the fact that total of macro-repositioning movements did not change. Conclusion Future research should evaluate the effect of tilting systems that provide macro-repositioning in a controlled form, not like in this study. Also, it is necessary to study if these types of automatic systems contribute to the reduction of the discomfort due to a prolonged period in the sitting posture.

Prolonged Intermittent Trunk Flexion Increases Trunk Muscles Reflex Gains and Trunk Stiffness

The goal of the present study was to determine the effects of prolonged, intermittent flexion on trunk neuromuscular control. Furthermore, the potential beneficial effects of passive upper body support during flexion were investigated. Twenty one healthy young volunteers participated during two separate visits in which they performed 1 hour of intermittent 60 seconds flexion and 30 seconds rest cycles. Flexion was set at 80% lumbar flexion and was performed with or without upper body support. Before and after intermittent flexion exposure, lumbar range of motion was measured using inertial measurement units and trunk stability was assessed during perturbations applied in the forward direction with a force controlled actuator. Closed-loop system identification was used to determine the trunk translational admittance and reflexes as frequency response functions. The admittance describes the actuator displacement as a function of contact force and to assess reflexes muscle activation was related to actuator displacement. Trunk admittance gain decreased after unsupported flexion, while reflex gain and lumbar range of motion increased after both conditions. Significant interaction effects confirmed a larger increase in lumbar range of motion and reflex gains at most frequencies analysed following unsupported flexion in comparison to supported flexion, probably compensating for decreased passive tissue stiffness. In contrast with some previous studies we found that prolonged intermittent flexion decreased trunk admittance, which implies an increase of the lumped intrinsic and reflexive stiffness. This would compensate for decreased stiffness at the cost of an increase in cumulative low back load. Taking into account the differences between conditions it would be preferable to offer upper body support during activities that require prolonged trunk flexion.

Effect of chronic knee osteoarthritis on flexion-relaxation phenomenon of the erector spinae in elderly females

[Purpose] This study investigated the flexion-relaxation phenomenon of the erector spinae in elderly women with chronic knee osteoarthritis and determined whether the flexion-relaxation phenomenon can be used as a pain evaluation tool in such cases. [Subjects and Methods] Seventeen elderly females with chronic knee osteoarthritis and 13 healthy young females voluntarily participated in this study. They performed three postural positions in 15 s: trunk flexion, complete trunk flexion, and trunk extension, each for 5 s. While these positions were held, muscle activation of the thoracic and lumbar erector spinae were measured using surface electromyography. The flexion-relaxation rate was determined by dividing the values for trunk extension by those of complete trunk flexion and by dividing the values for trunk flexion by those of complete trunk flexion. [Results] According to our results, the flexion-relaxation phenomenon was different between healthy young and elderly females with chronic knee osteoarthritis. Specifically, there was a difference in the left thoracic erector spinae muscle, but not in the left and right lumbar erector spinae or right thoracic spinae muscle. [Conclusion] Our study demonstrated that the erector spinae muscle flexion-relaxation phenomenon can be used as a pain evaluation tool in elderly females with chronic knee osteoarthritis.

Working position influences the biomechanical demands on the lower back during dental hygiene

This investigation monitored the biomechanical demands on the lower back during simulated dental hygiene work. A total of 19 female, registered dental hygienists performed 30 continuous minutes of manual scaling (plaque removal) of a manikin's teeth while seated. We monitored the working location and orientation of the dental hygienists, with respect to the manikin, along with their spine kinematics, spine extensor muscle activities and seat pressure, throughout the 30 min. A clock representation was used to express the working location. The location significantly influenced the dental hygienists' pelvic orientation with respect to the manikin, spine posture, erector muscle activity and pressure distribution. Findings from this study suggest that the prevalence of lower back pain amongst dental hygienists may be directly related to low-level tonic activity of the spine's extensor musculature, and the combined flexed and axially rotated spine postures. Practitioner Summary: Low back pain (LBP) is prevalent in dental hygienists, yet occupational demand on the low back has not been investigated. Posture, muscle activity and seat pressure were monitored. Combined spine rotation and flexion, and tonic activity of the extensor musculature may be related to LBP in dental hygienists.

Comparison of activation and change in the upper trapezius muscle during painful and non-painful computer work

[Purpose] Activation and changes in parts of the upper trapezius muscle during painful and non-painful computer work were compared. [Subjects] Ten male computer workers were recruited. [Methods] Surface electromyography was used to compare upper trapezius muscle activation and changes (difference between minimum and maximum activation) during painful and non-painful computer work. [Results] Mean normalized upper trapezius muscle activity did not differ between the “feel-pain” and “non-feel-pain” muscle sections. The mean change in upper trapezius muscle activity in the feel-pain section decreased significantly compared to the non-feel-pain section. [Conclusion] Measuring changes in the activity of muscle sections was useful to study static and sustained muscle stress during computer work.

Task-specificity of bilateral anticipatory activation of the deep abdominal muscles in healthy and chronic low back pain populations

STUDY DESIGN

Cross-sectional study of lumbopelvic muscle activation during rapid limb movements in chronic low back pain (CLBP) patients and healthy controls.

INTRODUCTION

Controversy exists over whether bilateral anticipatory activation of the deep abdominal muscles represents a normal motor control strategy prior to all rapid limb movements, or if this is simply a task-specific strategy appropriate for only certain movement conditions.

OBJECTIVE

To assess the onset timing of the transversus abdominis/internal oblique muscles (TrA/IO) during two rapid limb movement tasks with different postural demands - bilateral shoulder flexion in standing, unilateral hip extension in prone lying - as well as differences between CLBP and controls.

METHODS

Twelve CLBP and 13 controls performed the two tasks in response to an auditory cue. Surface EMG was acquired bilaterally from five muscles, including TrA/IO.

RESULTS

In both groups, 50% of bilateral shoulder flexion trials showed bilateral anticipatory TrA/IO activation. This was rare, however, in unilateral hip extension for which only the TrA/IO contralateral to the moving leg showed anticipatory activation. The only significant difference in lumbo-pelvic muscle onset timing between CLBP and controls was a delay in semitendinosus activation during bilateral shoulder flexion in standing.

CONCLUSION

Our data suggest that bilateral anticipatory TrA/IO activation is a task-specific motor control strategy, appropriate for only certain rapid limb movement conditions. Furthermore, the presence of altered semitendinosus onset timing in the CLBP group during bilateral shoulder flexion may be reflective of other possible lumbo-pelvic motor control alterations among this population.

Comparison of the T10 and L4 paraspinal muscle activities over time during continuous computer work

[Purpose] This study compared the T10 and L4 paraspinal muscle activities over time during continuous computer work. [Subjects] Ten male workers participated in this study. [Methods] The T10 and L4 paraspinal muscle activities were measured using a surface EMG system after 0, 20, 40, and 80 minutes of continuous computer work. [Results] The T10 and L4 paraspinal muscle activities after 20 and 40 minutes were increased significantly compared with the initial values, while they were decreased significantly after 80 minutes compared with the initial readings. [Conclusion] This study suggests that workers using computers for short periods would benefit from back muscle stretching exercises due to increased tension in these muscles. For longer computer work, strengthening exercises would be more effective than stretching due to decreased back muscle activation.

Quantification of the lumbar flexion-relaxation phenomenon: comparing outcomes of lumbar erector spinae and superficial lumbar multifidus in standing full trunk flexion and slumped sitting postures

OBJECTIVE

The purpose of this study was to identify differences in flexion-relaxation outcomes in asymptomatic participants, with respect to both flexion-relaxation phenomenon (FRP) occurrence and spinal onset angles, as a function of posture and choice of muscle being examined.

METHODS

This was a cross-sectional study in a laboratory setting. Thirty asymptomatic participants performed standing full trunk flexion and slumped sitting postures while activation levels of the lumbar erector spinae and superficial lumbar multifidus were monitored. Two thresholds were used to define whether FRP was present in each muscle and, if present, at what trunk flexion angle it occurred. These outcomes were compared descriptively between muscles and between postures.

RESULTS

Most participants displayed FRP in both muscles during standing full flexion; occurrences were more variable in slumped sitting. On average, FRP during standing full flexion and slumped sitting occurred at approximately 80% and 52% of participants' maximum flexion value, respectively. Variability in the slumped sitting onset angles was greater than that in standing full flexion.

CONCLUSION

Outcomes for FRP during standing full flexion in asymptomatic participants appeared to be more robust and were not affected by the choice of either lumbar erector spinae or superficial lumbar multifidus. Conversely, during slumped sitting, FRP occurrence varied substantially depending on choice of muscle, although onset angles were relatively consistent between muscles. Although the choice of one muscle over the other may be warranted, it may be prudent to examine both muscles during FRP investigations in sitting postures, in order to fully characterize the behavior and activation patterns of the lumbar musculature.

Objective classification of vehicle seat discomfort

The objective of this study was to identify how physiological measures relate to self-reported vehicle seating discomfort. Twelve subjects of varied anthropometric characteristics were enrolled in the study. Subjects sat in two seats over a 2-h period and were evaluated via three physiological measures (near-infrared spectroscopy, electromyography and pressure mapping) yielding six testing sessions. Subjective discomfort surveys were recorded before and after each session for nine regions of the body. Conditional classification discomfort models were developed through dichotomised physiological responses and anthropometry to predict subjective discomfort in specific body locations. Models revealed that subjects taller than 171 cm with reduced blood oxygenation in the biceps femoris or constant, low-level muscle activity in the trapezius tended to report discomfort in the lower extremities or neck, respectively. Subjects weighing less than 58 kg with reduced blood oxygenation in the biceps femoris or unevenly distributed pressure patterns tended to report discomfort in the buttocks. The sensitivities and specificities of cross-validated models ranged between 0.69 and 1.00.

Improving Field Observation of Spinal Posture in Sitting

Observing seated posture is important for ergonomic assessment; proper chair fit and chair adjustment should be considered for the entire context of work demands. Recommending only one seated posture presumes that all seated work has a similar location of visual targets, shoulder reach distances, and support surfaces. The nature of work tasks may influence posture more than does chair adjustment, and field observation of sitting should focus specifically on lumbar spine posture when work may cause forward movement of the torso. I suggest that the position and movement of the pelvis in relation to the torso is a reasonable and important indicator of spinal posture.

Transient pain developers show increased abdominal muscle activity during prolonged sitting

BACKGROUND

Sitting is a commonly adopted posture during work and prolonged exposures may have detrimental effects. Little attention has been paid to the thoracic spine and/or multiple axes of motion during prolonged sitting. Accordingly, this study examined three-dimensional motion and muscle activity of the trunk during two hours of uninterrupted sitting.

METHODS

Ten asymptomatic males sat during a simulated office task. Kinematics were analyzed from six segments (Neck, Upper-, Mid-, and Lower-thoracic, Lumbar, and Pelvis) and electromyography was recorded from eight muscles bilaterally.

RESULTS

Four participants developed transient pain. These participants showed higher average muscle activations in the abdominal muscles. Additionally, the non-pain group showed less lateral bend positional change in the mid-thoracic region compared to the upper- and lower-thoracic regions. Weak-to-moderate positive correlations were also found between rated pain and low back muscle activation.

DISCUSSION

The results provided further evidence of reduced movement in non-pain developers and altered muscle activation patterns in pain developers. Low-level, prolonged static contractions could lead to an increased risk of injury; and though the increased abdominal activity in the pain developers was not directly associated with increased rated pain scores, this could indicate a pre-disposition to, or enhancer of, transient pain development.

Evaluation of methods for the quantification of the flexion-relaxation phenomenon in the lumbar erector spinae muscles

OBJECTIVES

There are various methods to quantify the flexion-relaxation phenomenon (FRP); however, there is little standardization. This study aimed to evaluate the performance of various quantification methods in terms of their ability to identify lumbar erector spinae flexion-relaxation during standing forward trunk flexion.

METHODS

The study was a cross-sectional design in a laboratory setting. Lumbar erector spinae activation levels were measured in 12 male participants performing full trunk flexion movements. Electromyographical signals were assessed using 16 criteria within 4 quantification methods (visual, statistical, threshold, ratio), and the sensitivity of each was assessed relative to the benchmark criterion (visual inspection of raw electromyography data).

RESULTS

Visual inspection and most of the threshold and ratio criteria displayed the highest sensitivity. On average (SD) across the 16 criteria, FRP was positively identified 21.6 (6.2) times of 24 data sets (12 participants, 2 muscles). The visual inspection criteria positively identified FRP in all 24 trials, whereas the statistical method did not identify FRP at all (P = .44 and P = .46 for the left and right sides, respectively). The threshold and ratio criteria positively identified FRP 23.2 (1.5) and 22.5 (3.7) times, on average, respectively. Results from criteria based on differences between upright and fully flexed muscle activation tended to be conservative in FRP identification. The methods were classified as reliable or nonreliable, based on their sensitivity when specific characteristics were evident in the electromyography signals.

CONCLUSIONS

Although many of the criteria identified FRP with 100% sensitivity, others produced unrealistic results. The latter may be suitable for other experimental designs or may require reevaluation regarding their ability to identify FRP. Although visual inspection, threshold, or ratio methods performed well and may be appropriate for either biomechanical or clinical research, the threshold method provided the optimal trade-off between performance, consistency, and feasibility for these data.

Efficacy of classification-based cognitive functional therapy in patients with non-specific chronic low back pain: a randomized controlled trial

BACKGROUND

Non-specific chronic low back pain disorders have been proven resistant to change, and there is still a lack of clear evidence for one specific treatment intervention being superior to another.

METHODS

This randomized controlled trial aimed to investigate the efficacy of a behavioural approach to management, classification-based cognitive functional therapy, compared with traditional manual therapy and exercise. Linear mixed models were used to estimate the group differences in treatment effects. Primary outcomes at 12-month follow-up were Oswestry Disability Index and pain intensity, measured with numeric rating scale. Inclusion criteria were as follows: age between 18 and 65 years, diagnosed with non-specific chronic low back pain for >3 months, localized pain from T12 to gluteal folds, provoked with postures, movement and activities. Oswestry Disability Index had to be >14% and pain intensity last 14 days >2/10. A total of 121 patients were randomized to either classification-based cognitive functional therapy group n = 62) or manual therapy and exercise group (n > = 59).

RESULTS

The classification-based cognitive functional therapy group displayed significantly superior outcomes to the manual therapy and exercise group, both statistically (p < 0.001) and clinically. For Oswestry Disability Index, the classification-based cognitive functional therapy group improved by 13.7 points, and the manual therapy and exercise group by 5.5 points. For pain intensity, the classification-based cognitive functional therapy improved by 3.2 points, and the manual therapy and exercise group by 1.5 points.

CONCLUSIONS

The classification-based cognitive functional therapy produced superior outcomes for non-specific chronic low back pain compared with traditional manual therapy and exercise.

What is slumped sitting? A kinematic and electromyographical evaluation

Slumped sitting is a commonly used reference posture when comparing effects of upright sitting in both clinical and non-clinical populations alike. The exact nature of slumped sitting has not been clearly defined, including regional differences within the posture, and how the passive nature of slumped sitting compares to an active-flexion posture. Kinematic and electromyographical (EMG) data were collected from 12 males during three repeats of slumped sitting and seated maximum forward flexion. Spine angles were defined in four regions (three thoracic and lumbar) as well as for the pelvis, and EMG was collected from eight muscles bilaterally. Kinematic data were expressed as a range of motion (in degrees), and as a percent of full forward flexion while seated (%SIT-FF) and standing (%STAND-FF). EMG data were normalized to a percent maximum contraction (%MVC). Results showed that slumped sitting is characterized by 10° posterior pelvis rotation, near end-range flexion of the mid- (90%SIT-FF) and lower- (81%SIT-FF) thoracic regions, and mid-range flexion of the upper-thoracic (51%SIT-FF) and lumbar (43%SIT-FF) regions. Comparison of slumped by %STAND-FF showed the upper- and mid-thoracic regions to have high variability and large values (over 100%STAND-FF). Muscle activation showed a significant 3%MVC reduction in the lower-thoracic erector spinae muscle when moving from upright to slumped sitting. These data highlight the postural differences occurring within different spine regions, and interpretations that could be drawn, depending on which normalization (sit or stand) method is used.

Short term modulation of trunk neuromuscular responses following spinal manipulation: a control group study

Background

Low back pain (LBP) is one of the most frequent musculoskeletal conditions in industrialized countries and its economic impact is important. Spinal manipulation therapy (SMT) is believed to be a valid approach in the treatment of both acute and chronic LBP. It has also been shown that SMT can modulate the electromyographic (EMG) activity of the paraspinal muscle. The purpose of this study was to investigate, in a group of patients with low back pain, the persistence of changes observed in trunk neuromuscular responses after a spinal manipulation (SMT).

Methods

Sixty adult participants with LBP performed a block of 5 flexion-extension movements. Participants in the experimental group (n=30) received lumbar SMT whereas participants in the control group (n=30) were positioned similarly for the treatment but did not receive SMT. Blocks of flexion-extension movements were repeated immediately after the manipulation as well as 5 and 30 minutes after SMT (or control position). EMG activity of paraspinal muscles was recorded at L2 and L5 level and kinematic data were collected to evaluate the lumbo-pelvic kinematics. Pain intensity was noted after each block. Normalized EMG, pain intensity and lumbo-pelvic kinematics were compared across experimental conditions.

Results

Participants from the control group showed a significant increase in EMG activity during the last block (30 min) of flexion-extension trials in both flexion and full-flexion phases at L2. Increase in VAS scores was also observed in the last 2 blocks (5 min and 30 min) in the control group. No significant group x time interaction was seen at L5. No significant difference was observed in the lumbo-pelvic kinematics.

Conclusion

Changes in trunk neuromuscular control following HVLA spinal manipulation may reduce sensitization or muscle fatigue effects related to repetitive movement. Future studies should investigate short term changes in neuromuscular components, tissue properties and clinical outcomes.

Does prolonged seated deskwork alter the lumbar flexion relaxation phenomenon?

Sustained maximum lumbar spine flexion can increase the angle at which the low back flexion relaxation phenomenon (FRP) is observed. This adaptation has been hypothesized to have implications for the control of lumbar spine stability and increase the potential for low back injury. The objective of this study was to investigate if similar changes in the FRP would occur from sub-maximal spine flexion induced by an extended continuous duration of seated office deskwork. Twenty-three participants (12 male and 11 female) performed three bouts of full forward spine flexion interspersed with two 1-h periods of seated deskwork. Lumbar spine angular kinematics and electromyographic activity from the lumbar erector spinae were obtained throughout all trials. The angles at which myoelectric silence occurred (FRP onset) were documented. Lumbar flexion at FRP onset increased by 1.3±1.5° after 1-h of sitting (p<0.05) with no further increase after 2-h. However, when the angle at the FRP onset was normalized to the total range of flexion, there was no difference in the FRP onset. These results suggest that the seated posture may induce residual deformation in the viscoelastic passive tissues of the low back; this could increase the challenge of controlling spine motion and reduce the load-bearing capacity of the lumbar spine system during activities performed following extended bouts of sitting.

High frequency of McKenzie's postural syndrome in young population of non-care seeking individuals

OBJECTIVES

The role of postural loads as a risk factor for back pain and musculoskeletal symptoms is unclear. McKenzie proposed in his classification of mechanical syndromes a postural syndrome, in which people only develop symptoms from sustained loading, which is relieved by a change in position and has no effect on movement or function. Because of the low level disability with postural syndrome, it was suggested that few seek healthcare for this problem.

METHODS

This study used a two-stage process first to give a questionnaire to 100 students and staff from a university to determine who appeared to have postural syndrome, and then applied a physical examination to those who consented.

RESULTS

One hundred and thirty-eight were approached, of who 100 completed questionnaires and 66% appeared to have postural syndrome. Of the 66 who appeared to have postural syndrome, 37 consented to have a physical examination. Of the 37, 31 met the criteria for postural syndrome, with postural syndrome being significantly associated with pain on sustained loading and pain abolition on posture correction. Most postural syndrome was in the lumbar spine and associated with sitting, but other sites and causes were also noted.

DISCUSSION

This study lends credibility to McKenzie's postural syndrome, but also suggests this as a possible precursor for future more disabling or painful problems. Postural syndrome may not feature in those seeking professional healthcare, but is clearly highly prevalent in a young population.

Comparing lower lumbar kinematics in cyclists with low back pain (flexion pattern) versus asymptomatic controls--field study using a wireless posture monitoring system

The aim of this study was to examine lower lumbar kinematics in cyclists with and without non-specific chronic low back pain (NS-CLBP) during a cross-sectional cycling field study. Although LBP is a common problem among cyclists, studies investigating the causes of LBP during cycling are scarce and are mainly focussed on geometric bike-related variables. Until now no cycling field studies have investigated the relationship between maladaptive lumbar kinematics and LBP during cycling. Eight cyclists with NS-CLBP classified as having a 'Flexion Pattern' (FP) disorder and nine age- and gender-matched asymptomatic cyclists were tested. Subjects performed a 2 h outdoor cycling task on their personal race bike. Lower lumbar kinematics was measured with the BodyGuard™ monitoring system. Pain intensity during and after cycling was measured using a numerical pain rating scale. The NS-CLBP (FP) subjects were significantly more flexed at the lower lumbar spine during cycling compared to healthy controls (p = 0.018), and reported a significant increase in pain over the 2 h of cycling (p < 0.001). One-way repeated measures ANOVA revealed a significant main effect for group (p = 0.035, F = 5.546) which remained just significant when adding saddle angle as a covariate (p = 0.05, F = 4.747). The difference in posture between groups did not change over time. These findings suggest that a subgroup of cyclists with NS-CLBP (FP) demonstrate an underlying maladaptive motor control pattern resulting in greater lower lumbar flexion during cycling which is related to a significant increase in pain.

A comparison study on the change in lumbar lordosis when standing, sitting on a chair, and sitting on the floor in normal individuals

Objective

To compare radiographic analysis on the sagittal lumbar curve when standing, sitting on a chair, and sitting on the floor.

Methods

Thirty asymptomatic volunteers without a history of spinal pathology were recruited. The study population comprised 11 women and 19 men with a mean age of 29.8 years. An independent observer assessed whole lumbar lordosis (WL) and segmental lordosis (SL) between L1 and S1 using the Cobb's angle on lateral radiographs of the lumbar spine obtained from normal individuals when standing, sitting on a chair, and sitting on the floor. WL and SL at each segment were compared for each position.

Results

WL when sitting on the floor was reduced by 72.9% than the average of that in the standing position. Of the total decrease in WL, 78% occurred between L4 to S1. There were significant decreases in SL at all lumbar spinal levels, except L1-2, when sitting on the floor as compared to when standing and sitting on a chair. Changes in WL between the positions when sitting on a chair and when sitting on the floor were mostly contributed by the loss of SL at the L4-5 and L5-S1 levels.

Conclusion

When sitting on the floor, WL is relatively low; this is mostly because of decreasing lordosis at the L4-5 and L5-S1 levels. In the case of lower lumbar fusion, hyperflexion is expected at the adjacent segment when sitting on the floor. To avoid this, sitting with a lordotic lumbar curve is important. Surgeons should remember to create sufficient lordosis when performing lower lumbar fusion surgery in patients with an oriental life style.

Lumbar posture and trunk muscle activation during a typing task when sitting on a novel dynamic ergonomic chair

Low back pain (LBP) is a common musculoskeletal disorder and prolonged sitting often aggravates LBP. A novel dynamic ergonomic chair ('Back App'), which facilitates less hip flexion while sitting on an unstable base has been developed. This study compared lumbar posture and trunk muscle activation on this novel chair with a standard backless office chair. Twelve painfree participants completed a typing task on both chairs. Lumbar posture and trunk muscle activation were collected simultaneously and were analysed using paired t-tests. Sitting on the novel dynamic chair significantly (p < 0.05) reduced both lumbar flexion and the activation of one back muscle (Iliocostalis Lumborum pars Thoracis). The discomfort experienced was mild and was similar (p > 0.05) between chairs. Maintaining lordosis with less muscle activation during prolonged sitting could reduce the fatigue associated with upright sitting postures. Studies with longer sitting durations, and in people with LBP, are required.

PRACTITIONER SUMMARY

Sitting on a novel dynamic chair resulted in less lumbar flexion and less back muscle activation than sitting on a standard backless office chair during a typing task among pain-free participants. Facilitating lordotic sitting with less muscle activation may reduce the fatigue and discomfort often associated with lordotic sitting postures.

Association of spinal muscle composition and prevalence of hyperkyphosis in healthy community-dwelling older men and women

BACKGROUND

Older adults with hyperkyphosis are at increased risk of falls, fractures, and functional decline. Modifiable risk factors for hyperkyphosis have not been well studied. Our objective was to determine whether spinal muscle area and density are associated with hyperkyphosis, independent of age, race, sex, bone mineral density, and trunk fat.

METHODS

Using data from the Pittsburgh site of the Health, Aging, and Body Composition study, we performed a baseline cross-sectional analysis. Participants were black and white men and women 70-79 years old (N = 1172), independent in activities of daily living and able to walk &frac14; mile and up 10 steps without resting. We measured Cobb's angle of kyphosis from supine lateral scout computed tomography scans, and categorized hyperkyphosis as Cobb's angle >40°. Axial images from lateral scout computed tomography scans assessed spinal extensor muscle cross-sectional area and density (proxy for fat infiltration).

RESULTS

In our sample, 21% had hyperkyphosis. Prevalence in black men was 11%; in white men, 17%; in black women, 26%; and in white women, 30%. In multivariate analysis, each standard deviation increase in muscle density was associated with a 29% reduction in the odds of hyperkyphosis, independent of covariates. Muscle area was not significantly associated with hyperkyphosis.

CONCLUSIONS

Lower spinal muscle density is associated with hyperkyphosis in healthy community-dwelling older adults. This potentially modifiable risk factor could be targeted in exercise interventions. Randomized trials are needed to determine whether an exercise program targeting spinal muscle density reduces hyperkyphosis and in turn improves health outcomes.

Effects of a Visual Feedback Device for Hip Adduction on Trunk Muscles and Sitting Posture in Visual Display Terminal Workers

This study was designed to identify the effects of a visual feedback device for hip adduction on trunk muscles and sitting posture when working at a visual display terminal. The forward head and trunk flexion angles of 20 workers were analyzed using a motion analysis system, and the activities of the lower trapezius, external abdominal oblique, internal abdominal oblique, and L5 paraspinal muscles were analyzed using a electromyography system. The statistical significance of differences between using and not using a visual feedback device was assessed by paired t tests. Using the visual feedback device during Visual Display Terminal work significantly decreased the forward head and trunk flexion angles, and significantly increased the activities of the external abdominal oblique, internal abdominal oblique, and L5 paraspinal muscles. The authors suggest that the visual feedback device for hip adduction promotes the adoption of standard spine and pelvic postures, which might be effective in preventing poor sitting postures.

Association of biopsychosocial factors with degree of slump in sitting posture and self-report of back pain in adolescents: a cross-sectional study

BACKGROUND

Conflicting evidence exists regarding relationships among sitting posture, factors that influence sitting posture, and back pain. This conflicting evidence may partially be due to the presence of multiple and overlapping factors associated with both sitting posture and back pain.

OBJECTIVE

The purpose of this study was to determine whether the degree of slump in sitting was associated with sex and other physical, lifestyle, or psychosocial factors. Additionally, the relationship between the report of back pain made worse by sitting and the degree of slump in sitting and other physical, lifestyle, or psychosocial factors was investigated.

DESIGN

This was a cross-sectional study.

METHODS

Adolescents (n=1,596) completed questionnaires to determine lifestyle and psychosocial profiles and the experience of back pain. Sagittal sitting posture, body mass index (BMI), and back muscle endurance (BME) were recorded. Standing posture subgroup categorization was determined.

RESULTS

Multivariate analysis revealed that the most significant factor associated with the degree of slump in sitting was male sex, followed by non-neutral standing postures, lower perceived self-efficacy, lower BME, greater television use, and higher BMI. Multivariable analysis indicated poorer Child Behaviour Checklist scores were the strongest correlate of report of back pain made worse by sitting, whereas degree of slump in sitting, female sex, and BME were more weakly related.

LIMITATIONS

Causality cannot be determined from this cross-sectional study, and 60% of sitting posture variation was not explained by the measured variables.

CONCLUSIONS

Slump in sitting was associated with physical correlates, as well as sex, lifestyle, and psychosocial factors, highlighting the complex, multidimensional nature of usual sitting posture in adolescents. Additionally, this study demonstrated that a greater degree of slump in sitting was only weakly associated with adolescent back pain made worse by sitting after adjustment for other physical and psychosocial factors.

Flexion-relaxation ratio in sitting: application in low back pain rehabilitation

STUDY DESIGN

A multiple-comparative study between normal and low back pain (LBP) patients before and after rehabilitation.

OBJECTIVE

To examine whether there is a change in flexion-relaxation phenomenon in sitting in LBP patient following a rehabilitation treatment.

SUMMARY OF BACKGROUND DATA

There is an association between LBP and seated spine posture. Previous study has reported an absence of flexion-relaxation phenomenon in LBP patients during sitting. However, it is unknown whether there is a difference in flexion-relaxation phenomenon in sitting in LBP patients before and after rehabilitation treatment.

METHODS

A total of 20 normal subjects and 25 chronic LBP patients who underwent a 12 weeks rehabilitation program were recruited. Surface electromyography recordings during upright sitting and flexed sitting were taken from the paraspinal muscles (L3) bilaterally from the normal subjects, and in the LBP patients before and after the rehabilitation treatment. The main outcome measures for patients include the visual analogue scale, Oswestry disability index, subjective tolerance for sitting, standing and walking, trunk muscle endurance, lifting capacity, and range of trunk motion in the sagittal plane. Flexion-relaxation phenomenon in sitting, expressed as a ratio between the average surface electromyography activity during upright and flexed sitting, was compared between normal and patients; and in LBP patients before and after rehabilitation.

RESULTS

Flexion-relaxation ratio in sitting in normal subjects (Left: 6.83 +/- 3.79; Right: 3.45 +/- 2.2) presented a significantly higher (Left: P < 0.001; Right: P < 0.05) value than LBP patients (Left: 3.04 +/- 2.36; Right: 2.02 +/- 1.49). An increase in flexion-relaxation ratio in sitting was observed in LBP patients after rehabilitation (Left: 4.69 +/- 3.94, P < 0.05; Right: 3.58 +/- 2.97, P < 0.001), together with a significant improvement (P < 0.05) in subjective tolerance in sitting and standing, abdominal and back muscle endurance, lifting capacity, and range of motion. There were no significant changes in disability and pain scores, and subjective tolerance in walking.

CONCLUSION

Flexion-relaxation ratio in sitting has demonstrated its ability to discriminate LBP patients from normal subjects, and to identify changes in pattern of muscular activity during postural control after rehabilitation.

Sitting postures and trunk muscle activity in adolescents with and without nonspecific chronic low back pain: an analysis based on subclassification

STUDY DESIGN

A preliminary cross-sectional comparative study of adolescents with nonspecific chronic low back pain (NSCLBP) and healthy controls.

OBJECTIVE

To investigate whether differences in spinal kinematic and trunk muscle activity exist in both usual and slump sitting in adolescents with NSCLBP.

SUMMARY OF BACKGROUND

Evidence suggests that low back pain commonly develops in adolescence and increases the risk for low back pain in adulthood. Sitting is an important consideration in adolescents with NSCLBP: currently there are no reports investigating their motor control strategies in sitting.

METHODS

Twenty-eight adolescents (14 female) with NSCLBP and 28 matched pain-free controls were recruited from a large cohort study. Pain subjects were subclassified based on O'Sullivan's classification system. Three-dimensional lumbo-pelvic kinematic data and the activation of 3 back and 2 abdominal muscles were recorded during usual and slump sitting. The flexion-relaxation phenomenon in sitting was also investigated.

RESULTS

Spinal posture in usual and slump sitting were similar for adolescents with and without NSCLBP. However, differences were identified in both sitting conditions when those with NSCLPB were subclassified and compared with controls. Muscle activation differences were not consistently identified, with only lower levels of internal oblique activation in usual sitting in NSCLBP compared with pain-free controls showing significance. Flexion relaxation was observed in both iliocostalis and thoracic erector spinae in the NSCLBP group but not controls.

CONCLUSION

This study provides preliminary results. Differences with sitting posture are only seen when adolescents with NSCLBP are classified. Trunk muscle activation is not a sensitive marker for discriminating subgroups of NSCLBP during adolescence.

Changes in the flexion-relaxation response induced by hip extensor and erector spinae muscle fatigue

Background

The flexion-relaxation phenomenon (FRP) is defined by reduced lumbar erector spinae (ES) muscle myoelectric activity during full trunk flexion. The objectives of this study were to quantify the effect of hip and back extensor muscle fatigue on FRP parameters and lumbopelvic kinematics.

Methods

Twenty-seven healthy adults performed flexion-extension tasks under 4 different experimental conditions: no fatigue/no load, no fatigue/load, fatigue/no load, and fatigue/load. Total flexion angle corresponding to the onset and cessation of myoelectric silence, hip flexion angle, lumbar flexion angle and maximal trunk flexion angle were compared across different experimental conditions by 2 × 2 (Load × Fatigue) repeated-measures ANOVA.

Results

The angle corresponding to the ES onset of myoelectric silence was reduced after the fatigue task, and loading the spine decreased the lumbar contribution to motion compared to the hip during both flexion and extension. A relative increment of lumbar spine motion compared to pelvic motion was also observed in fatigue conditions.

Conclusions

Previous results suggested that ES muscles, in a state of fatigue, are unable to provide sufficient segmental stabilization. The present findings indicate that, changes in lumbar-stabilizing mechanisms in the presence of muscle fatigue seem to be caused by modulation of lumbopelvic kinematics.