Timing of activation of the erector spinae and hamstrings during a trunk flexion and extension task

Biomechanical Demands and User Preference Associated with Wall-Mounted and Rim-Mounted Grab Bars

Background. Grab bars are used to support bathing tasks. Sometimes, temporary rim-mounted grab bars may be preferred over permanent wall-mounted grab bars. Purpose. We compared postural requirements, applied loads, and user perceptions between two configurations of rim-mounted grab bars, a vertical wall-mounted grab bar, and a no-grab bar condition. Method. Ten adults entered and exited a simulated bathing environment. Trunk flexion was evaluated via 3D kinematics, while load cells mounted to the grab bars facilitated the evaluation of applied loads. Participants rated each condition on perceived safety, comfort, effectiveness, and ease of use. Findings. Rim-mounted grab bars resulted in greater trunk flexion and greater applied loads and were less favorably perceived. Implications. The rim-mounted grab bars included in this study may induce challenging postural demands and loading scenarios, and occupational therapists should consider whether they meet the needs of their clients.

The association between different physical activity levels and flexion-relaxation phenomenon in women: a cross-sectional study

BACKGROUND

To investigate whether the flexion-relaxation phenomenon differs in women with different physical activity levels.

METHODS

Seventy-two subjects were recruited for this study. The electromyographic activity of the erector spinae and multifidus muscles was recorded during a flexion task using a surface electromyographic device. The flexion-relaxation and extension-relaxation ratios were calculated. Participants were classified into different physical activity level groups based on their responses to the International Physical Activity Questionnaire. A Welch analysis of variance was conducted to compare the flexion-relaxation ratio and extension-relaxation ratio between groups.

RESULTS

A significant difference in the flexion-relaxation and extension-relaxation ratio was observed in both the erector spinae and multifidus muscles between different levels of physical activity.

CONCLUSIONS

In this study, we observed that female participants with high levels of physical activity showed a more pronounced flexion-relaxation phenomenon compared to those with moderate and low levels of physical activity. No significant difference was found between moderate and low physical activity levels. The findings of our study highlight the association between physical activity and the mechanics of the spinal stabilising muscles.

Effects of lumbar joint mobilization on trunk function, postural balance, and gait in patients with chronic stroke: A randomized pilot study

BACKGROUND

Patients with stroke have hypomobility in the facet joint of affected side. Lumbar joint mobilization could be used to maintain function and mobility of the joints.

OBJECTIVE

This study aimed to investigate the effects of lumbar joint mobilization on trunk function, postural balance, and gait in patients with stroke.

METHODS

Thirty patients with stroke were randomly assigned to two groups. Lumbar joint mobilization was provided for 15 min, 5 times a week for 6 weeks to patients who were allocated into the experimental group. Patients who were allocated into the control group received a sham intervention. Trunk function (trunk impairment scale), postural balance (weight distribution, Berg balance scale, and timed up and go test), and walking (10 m walk test, functional gait assessment, step length, and stride length) were evaluated before and after the experiment for all the patients.

RESULTS

Lumbar joint mobilization significantly improved trunk function, postural balance, and gait compared with pre-test values in the experimental group (P< 0.05). Significant differences were seen in trunk function, postural balance, and walking between the two groups (P< 0.05).

CONCLUSION

Lumbar joint mobilization might be an effective intervention for trunk function, postural balance, and walking in patients with stroke.

Reliability of high-density surface electromyography for assessing characteristics of the thoracic erector spinae during static and dynamic tasks

PURPOSE

To establish intra- and inter-session reliability of high-density surface electromyography (HDEMG)-derived parameters from the thoracic erector spinae (ES) during static and dynamic goal-directed voluntary movements of the trunk, and during functional reaching tasks.

METHODS

Twenty participants performed: 1) static trunk extension, 2) dynamic trunk forward and lateral flexion, and 3) multidirectional functional reaching tasks on two occasions separated by 7.5 ± 1.2 days. Muscle activity was recorded bilaterally from the thoracic ES. Root mean square (RMS), coordinates of the barycentre, mean frequency (MNF), and entropy were derived from the HDEMG signals. Reliability was determined with intraclass correlation coefficient (ICC), coefficient of variation, and standard error of measurement.

RESULTS

Good-to-excellent intra-session reliability was found for all parameters and tasks (ICC: 0.79-0.99), whereas inter-session reliability varied across tasks. Static tasks demonstrated higher reliability in most parameters compared to functional and dynamic tasks. Absolute RMS and MNF showed the highest overall reliability across tasks (ICC: 0.66-0.98), while reliability of the barycentre was influenced by the direction of the movements.

CONCLUSION

RMS and MNF derived from HDEMG show consistent inter-session reliability in goal-directed voluntary movements of the trunk and reaching tasks, whereas the measures of the barycentre and entropy demonstrate task-dependent reliability.

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.

Interrelated hypoalgesia, creep, and muscle fatigue following a repetitive trunk flexion exposure

Repetitive trunk flexion can damage spinal tissues, however its association with low back pain in the workplace may be confounded by factors related to pain sensitivity. Muscle fatigue, exercise-induced hypoalgesia, and creep-induced neuromuscular changes following repetitive trunk flexion may all affect this assumed exposure-pain relationship. This study's purpose was to determine how mechanical pain sensitivity in the low back is affected by a repetitive trunk flexion exposure and identify factors associated with changes in low back pain sensitivity. Pressure pain thresholds, perceptions of sub-threshold stimuli, and muscle fatigue in the trunk and tibia, as well as lumbar spine creep were tracked in 37 young healthy adults before and up to 40 min after a 10-min repetitive trunk flexion exposure. Pressure pain thresholds (p = 0.033), but not perceptions of sub-threshold stimuli (p > 0.102) were associated with approximately a 12.5% reduction in pain sensitivity 10 min after completing the exposure, while creep and local muscle fatigue effects were only observed immediately following the exposure. Creep and fatigue interactions and the corresponding tibial measure co-varied with individual low back pressure pain thresholds. The net hypoalgesic effects of repetitive trunk flexion have the potential to partially mask possibly injurious loads, which could contribute to the severity or incidence of lower back injuries related to these exposures.

Influence of Sacroiliac Bracing on Muscle Activation Strategies During 2 Functional Tasks in Standing-Tolerant and Standing-Intolerant Individuals

People who develop low back pain during standing (standing-intolerant) are a subclinical group at risk for clinical low back pain. Standing-intolerant individuals respond favorably to stabilization exercise and may be similar to people with sacroiliac joint dysfunction that respond to stabilization approaches including sacroiliac joint (SIJ) bracing. The purpose was to characterize muscle activation and response to SIJ bracing in standing-tolerant and standing-intolerant individuals during forward flexion and unilateral stance. Trunk and hip electromyography data were collected from 31 participants (17 standing-tolerant and 14 standing-intolerant) while performing these tasks with and without SIJ bracing. Kinematics were captured concurrently and used for movement phase identification. Cross-correlation quantified trunk coactivation and extensor timing during return-to-stand from forward flexion; root mean square amplitude quantified gluteal activity during unilateral stance. The standing-intolerant group had elevated erector spinae-external oblique coactivation without bracing, and erector spinae-internal oblique coactivation with bracing during return-to-stand compared with standing-tolerant individuals. Both groups reversed extensor sequencing during return-to-stand with bracing. Standing-tolerant individuals had higher hip abductor activity in nondominant unilateral stance and increased hip extensor activity with bracing. SIJ bracing could be a useful adjunct to other interventions targeted toward facilitating appropriate muscle activation in standing-intolerant individuals.

Muscular Activation Pattern of Bilateral Extensors Response to Asymmetric Hand Lifting During Trunk Flexion-extension Performance

The authors' purpose was to test the effect of asymmetric hand lifting on muscular activation patterns of 3 bilateral extensors. Eighteen male university students without back pain were volunteered. Each performed flexion-extension randomly with conditions of right lifting, left lifting, and nonlifting. Surface electromyography from bilateral thoracic, lumbar erector spinae, and hamstring was recorded. The cross-correlation and relative intensity in paired muscles of bilateral extensors was calculated in flexion as well as extension period. The results showed that the cross-correlation coefficient was decreased and the phase lag as well as the relative intensity of bilateral extensors was increased significantly in thoracic level. The phase lag as well as the relative intensity of bilateral extensors was increased significantly in lumbar level. It was concluded that asymmetric lifting has a significant effect on muscular activation of bilateral extensors in thorax level, which causes the ipsilateral extensor to activate larger and longer. Asymmetric lifting also has some effect on muscular activation of bilateral extensors in lumbar level but with less extent than in thorax level, which causes contralateral extensor to activate larger and longer. Asymmetric lifting seems to have no significant effect on muscular activation of bilateral hamstring.

Differences in lumbopelvic rhythm between trunk flexion and extension

BACKGROUND

Trunk flexion and extension have already been found to have different characteristics, such as those in lumbopelvic rhythm. Although a more advanced method of quantifying such rhythm, lumbopelvic continuous relative phase and phase variability have not been used to explore the differences between trunk flexion and extension motions. This information is important since abnormal lumbopelvic coordination patterns increase the risk of low back pain. The current study investigated the differences in lumbopelvic rhythm between trunk flexion and extension, and how the rhythm changed within each of the two motions.

METHODS

Thirteen subjects performed pace-controlled trunk flexion/extension motions in the sagittal plane while lumbar and pelvis kinematics data were recorded, such that the lumbopelvic continuous relative phase and phase variability could be calculated to quantify lumbopelvic rhythm.

FINDINGS

Trunk extension motion had significantly smaller lumbopelvic continuous relative phase and phase variability than flexion motion, which indicated a more in-phase and stable rhythm. Additionally, the lumbopelvic rhythm within trunk extension motion changed from a more in-phase and stable pattern to a more out-of-phase and unstable pattern; by contrast, the opposite change (from out-of-phase and unstable to in-phase and stable) was observed in trunk flexion.

INTERPRETATION

Findings of the current study provided important information about the differences in lumbopelvic rhythm between trunk flexion and extension motions. Quantifying these patterns provides the means for identifying abnormal patterns in a clinical setting, and could serve as normative benchmarks during low back pain rehabilitation plans.

Comparison of the Hamstring Muscle Activity and Flexion-Relaxation Ratio between Asymptomatic Persons and Computer Work-related Low Back Pain Sufferers

[Purpose] The purpose of this study was to compare the hamstring muscle (HAM) activities and flexion-relaxation ratios of an asymptomatic group and a computer work-related low back pain (LBP) group. [Subjects] For this study, we recruited 10 asymptomatic computer workers and 10 computer workers with work-related LBP. [Methods] We measured the RMS activity of each phase (flexion, full-flexion, and re-extension phase) of trunk flexion and calculated the flexion-relaxation (FR) ratio of the muscle activities of the flexion and full-flexion phases. [Results] In the computer work-related LBP group, the HAM muscle activity increased during the full-flexion phase compared to the asymptomatic group, and the FR ration was also significantly higher. [Conclusion] We thought that prolonged sitting of computer workers might cause the change in their HAM muscle activity pattern.

Differences between two subgroups of low back pain patients in lumbopelvic rotation and symmetry in the erector spinae and hamstring muscles during trunk flexion when standing

The present study was performed to examine lumbopelvic rotation and to identify asymmetry of the erector spinae and hamstring muscles in people with and without low back pain (LBP). The control group included 16 healthy subjects, the lumbar-flexion-rotation syndrome LBP group included 17 subjects, and the lumbar-extension-rotation syndrome LBP group included 14 subjects. Kinematic parameters were recorded using a 3D motion-capture system, and electromyography parameters were measured using a Noraxon TeleMyo 2400T. The two LBP subgroups showed significantly more lumbopelvic rotation during trunk flexion in standing than did the control group. The muscle activity and flexion-relaxation ratio asymmetries of the erector spinae muscles in the lumbar-flexion-rotation syndrome LBP group were significantly greater than those in the control group, and the muscle activity and flexion-relaxation ratio asymmetry of the hamstring muscles in the lumbar-extension-rotation syndrome LBP group were significantly greater than those in the control group. Imbalance or asymmetry of passive tissue could lead to asymmetry of muscular activation. Muscle imbalance can cause asymmetrical alignment or movements such as unexpected rotation. The results showed a greater increase in lumbopelvic rotation during trunk flexion in standing among the lumbar-flexion-rotation syndrome and lumbar-extension-rotation syndrome LBP groups compared with the control group. The differences between the two LBP subgroups may be a result of imbalance and asymmetry in erector spinae and hamstring muscle properties.

Altered muscle recruitment during extension from trunk flexion in low back pain developers

BACKGROUND

A functionally induced, transient low back pain model consisting of exposure to prolonged standing has been used to elucidate baseline neuromuscular differences between previously asymptomatic individuals classified as pain developers and non-pain developers based on their pain response during a standing exposure. Previous findings have included differences in frontal plane lumbopelvic control and altered movement strategies that are present prior to pain development. Control strategies during sagittal plane movement have not been previously investigated in this sample. The purpose of this research was to investigate neuromuscular control differences during the extension phase from trunk flexion between pain developers and non-pain developers.

METHODS

Continuous electromyography and kinematic data were collected during standing trunk flexion and extension on 43 participants (22 male) with an age range of 18-33 years, prior to entering into the prolonged standing exposure. Participants were classified as pain developer/non-pain developer by their pain response (≥ 10 mm increase on a 100 mm visual analog scale) during standing. Relative timing and sequencing data between muscle pairs were calculated through cross-correlation analyses, and evaluated by group and gender.

FINDINGS

Pain developers demonstrated a 'top-down' muscle recruitment strategy with lumbar extensors activated prior to gluteus maximus, while non-pain developers demonstrated a typical 'bottom-up' muscle recruitment strategy with gluteus maximus activated prior to lumbar extensors.

INTERPRETATION

Individuals predisposed to low back pain development during standing exhibited altered neuromuscular strategies prior to pain development. These findings may help to characterize biomechanical movement profiles that could be important for early identification of people at risk for low back pain.

Influence of asymmetry on the flexion relaxation response of the low back musculature

BACKGROUND

the flexion relaxation phenomenon has been extensively studied in sagittally symmetric postures. Knowledge about this phenomenon in asymmetric trunk postures is less well understood, and may help to reveal the underlying physiology of the passive tissue/active tissue load-sharing mechanism in the lumbar region.

METHODS

twelve participants performed fifteen controlled, full range trunk flexion-extension motions toward three asymmetric lifting postures (0° (sagittally symmetric), 15°, and 30° from the mid-sagittal plane). The electromyographic activity data from the paraspinals at the L3 and L4 levels and trunk kinematics data from motion sensors over the C7, T12 and S1 vertebrae were recorded. The lumbar flexion angles at which these muscles' activities were reduced to resting levels during forward flexion provided quantitative data describing the effects of asymmetry on the passive tissue/active tissue interaction.

FINDINGS

flexion relaxation was observed in the muscles contralateral to the direction of the asymmetric trunk flexion motion. The response of the ipsilateral extensor musculature was much less consistent, with many trials indicating that flexion relaxation was never achieved. Increasing asymmetry from 0° to 30° led to a 10% reduction in the maximum lumbar flexion. Lumbar flexion angles necessary to achieve flexion relaxation in the contralateral muscles also decreased (L4 paraspinal-related angle decreasing by 15% and the L3 paraspinal-related angle decreasing by 21%).

INTERPRETATION

under asymmetric conditions the lumbar flexion angle at which the transition from active muscle to passive ligamentous extension moment is altered from that seen in symmetric motions and this transition can have implications for the loading of the spine in full flexion (or near full flexion) postures.

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.

Interaction of viscoelastic tissue compliance with lumbar muscles during passive cyclic flexion-extension

Human and animal models using electromyography (EMG) based methods have hypothesized that viscoelastic tissue properties becomes compromised by prolonged repetitive cyclic trunk flexion-extension which in turn influences muscular activation including the flexion-relaxation phenomenon. Empirical evidence to support this hypothesis, especially the development of viscoelastic tension-relaxation and its associated muscular response in passive cyclic activity in humans, is incomplete. The objective of this study was to examine the response of lumbar muscles to tension-relaxation development of the viscoelastic tissue during prolonged passive cyclic trunk flexion-extension. Activity of the lumbar muscles remained low and steady during the passive exercise session. Tension supplied by the posterior viscoelastic tissues decreased over time without corresponding changes in muscular activity. Active flexion, following the passive flexion session, elicited significant increase in paraspinal muscles EMG together with increase in the median frequency. It was concluded that reduction of tension in the lumbar viscoelastic tissues of humans occurs during cyclic flexion-extension and is compensated by increased activity of the musculature in order to maintain stability. It was also concluded that the ligamento-muscular reflex is inhibited during passive activities but becomes hyperactive following active cyclic flexion, indicating that moment requirements are the controlling variable. It is conceived that prolonged routine exposure to cyclic flexion minimizes the function of the viscoelastic tissues and places increasing demands on the neuromuscular system which over time may lead to a disorder and possible exposure to injury.

Lengthening the hamstring muscles without stretching using "awareness through movement"

BACKGROUND AND PURPOSE

Passive stretching is widely used to increase muscle flexibility, but it has been shown that this process does not produce long-term changes in the viscoelastic properties of muscle as originally thought. The authors tested a method of lengthening hamstring muscles called "Awareness Through Movement" (ATM) that does not use passive stretching.

SUBJECTS

Thirty-three subjects who were randomly assigned to ATM and control groups met the screening criteria and completed the intervention phase of the study.

METHODS

The ATM group went through a process of learning complex active movements designed to increase length in the hamstring muscles. Hamstring muscle length was measured before and after intervention using the Active Knee Extension Test.

RESULTS

The ATM group gained significantly more hamstring muscle length (+7.04 degrees ) compared with the control group (+1.15 degrees ).

DISCUSSION AND CONCLUSION

The results suggest that muscle length can be increased through a process of active movement that does not involve stretching. Further research is needed to investigate this finding.

Flexion–relaxation response to gravity

The objective of this report was to study the influence of the orientation of gravitational loading on the behavior of anterior and posterior trunk muscles during anterior trunk flexion-extension. Participants (N=13) performed five (5) cycles of trunk flexion-extension while standing with gravity parallel to the body axis and five (5) cycles while in the supine condition (e.g. sit-ups) with gravity perpendicular to the body axis. Surface electromyographic (EMG) patterns from lumbar paraspinal, rectus abdominis, external oblique, rectus femoris, semimembranosis, and biceps femoris muscles were analyzed during each condition. EMG signals were synchronized with lumbar flexion and trunk inclination angles. Flexion-extension from the standing position resulted in a myoelectric silent period of the lumbar posterior muscles (e.g. flexion-relaxation phenomena (FRP)) as well as the hamstring muscles through deep angles during which activity was observed in abdominal muscles. Flexion-extension during sit-ups, however, resulted in a myoelectric silent period of the abdominal muscles and the quadriceps through deep angles during which the lumbar posterior muscles were active. In this condition, the FRP was not observed in posterior muscles. The new findings demonstrate the profound impact of the orientation of the gravity vector on the FRP, the abdominal muscles reaction to gravitational loads during sit-ups and its relationships with lumbar antagonists and thigh musculature. The new findings suggest that gravitational moments requirements dominate the FRP through the prevailing kinematics, load sharing and reflex activation-inhibition of muscles in various conditions. Lumbar kinematics or fixed sensory motor programs by themselves, however, are not the major contributor to the FRP. The new findings improve our insights into spinal biomechanics as well as understanding and evaluating low back disorders.

Trunk Repositioning Errors Are Increased in Balance-Impaired Older Adults

BACKGROUND

Controlling the flexing trunk is critical in recovering from a loss of balance and avoiding a fall. To investigate the relationship between trunk control and balance in older adults, we measured trunk repositioning accuracy in young and balance-impaired and unimpaired older adults.

METHODS

Young adults (N = 8, mean age 24.3 years) and two groups of community-dwelling older adults defined by unipedal stance time (UST)-a balance-unimpaired group (UST > 30 seconds, N = 7, mean age 73.9 years) and a balance-impaired group (UST < 5 seconds, N = 8, mean age 79.6 years)-were tested in standing trunk control ability by reproducing a approximately 30 degrees trunk flexion angle under three visual-surface conditions: eyes opened and closed on the floor, and eyes opened on foam. Errors in reproducing the angle were defined as trunk repositioning errors (TREs). Clinical measures related to balance, trunk extensor strength, and self-reported disability were obtained.

RESULTS

TREs were significantly greater in the balance-impaired group than in the other groups, even when controlling for trunk extensor strength and body mass. In older adults, there were significant correlations between TREs and three clinical measures of balance and fall risk, UST and maximum step length (-0.65 to -0.75), and Timed Up & Go score (0.55), and between TREs and age (0.63-0.76). In each group TREs were similar under the three visual-surface conditions. Test-retest reliability for TREs was good to excellent (intraclass correlation coefficients > or =0.74).

CONCLUSIONS

Older balance-impaired adults have larger TREs, and thus poorer trunk control, than do balance-unimpaired older individuals. TREs are reliable and valid measures of underlying balance impairment in older adults, and may eventually prove to be useful in predicting the ability to recover from losses of balance and to avoid falls.

Examination of the flexion relaxation phenomenon in erector spinae muscles during short duration slumped sitting

OBJECTIVE

The purpose of this study was to examine the myoelectric activity of the erector spinae muscles of the back in order to determine if the flexion relaxation phenomenon occurs in seated forward flexion or slumped postures.

BACKGROUND

The flexion relaxation phenomenon during standing forward flexion is well documented. However, flexion relaxation in seated forward flexion has not been studied. It is possible that flexion relaxation could be linked with low back pain that some individuals experience during seated work.

METHODS

Twenty-two healthy subjects (11 males, 11 females) participated in the study. Surface electromyography was used to measure the level of muscle activity at the thoracic and lumbar levels of the erector spinae muscles. An electromagnetic tracking device measured the three-dimensional movement of the lumbar spine. Five trials each of standing and seated forward flexion were performed.

RESULTS

A slumped sitting posture yielded flexion relaxation of the thoracic erector spinae muscles, whereas the lumbar erector spinae muscle group remained at relatively constant activation levels regardless of seated posture. Thoracic erector spinae silence occurred at a smaller angle of lumbar flexion during sitting than the flexion relaxation angle observed during standing flexion relaxation.

CONCLUSIONS

Since the myoelectric activity of the lumbar erector spinae did not increase, it is likely that the passive tissues of the vertebral column were loaded to support the moment at L4/L5. Ligaments contain a large number of free nerve endings which act as pain receptors and therefore could be a potential source of low back pain during seated work.

RELEVANCE

Examination of flexion relaxation during seated postures may provide insight into the association between low back pain and seated work.