Biomedical subjects

Jack P Callaghan

Publications and source records attributed to Jack P Callaghan.

17 recordsLinked to original sources

PubMed2006

Quantifying low back peak and cumulative loads in open and senior sheep shearers in New Zealand: examining the effects of a trunk harness.

Sheep shearing requires shearers to adopt sustained flexed postures for prolonged periods of time and has been associated with an increased risk of developing low back pain (LBP). However, these postures do not generally result in acute compressive values at L4/L5 exceeding the action limit proposed by the National Institute for Occupational Safety and Health, despite the high prevalence of LBP in this occupation. Therefore, it may not be peak loading that is responsible for LBP in this occupation but instead it may be the effect of cumulative loading over the course of a workday. The primary purpose of this research was to quantify the low back cumulative load exposure in 12 sheep shearers with and without the aid of a commercial trunk harness. Results revealed a significant reduction in the magnitude of cumulative compression with the use of the trunk harness and therefore its use may potentially reduce the risk of injury. The use of the trunk harness also reduced the time spent in axially twisted postures, which have been associated with LBP. However, using the trunk harness also resulted in increased time spent in laterally bent postures, which has been associated with increased risk for pain and injury.

Adult↗

PubMed2006

Do exercise balls provide a training advantage for trunk extensor exercises? A biomechanical evaluation.

OBJECTIVE: Only a few abdominal muscle exercises have been quantitatively evaluated on both a mat and exercise ball, but the benefits reported for the ball have been equivocally applied to all exercises. The purpose of this study is to evaluate differences in the biological response of muscle activation, lumbar spine posture, and loading variables for extensor exercises performed on 2 surfaces. METHODS: Bilateral muscle activation was recorded from 7 sites (rectus abdominis, external/internal obliques, latissimus dorsi, thoracic/lumbar erector spinae, and multifidus) on 8 subjects. Three-dimensional lumbar spine postures and upper body kinematics were recorded while the participants performed the exercises. An electromyography-driven model was used to calculate spinal loading. RESULTS: Cocontraction of trunk flexor and extensor muscles was reduced by up to 30% for the extension exercises when performed on the ball. Peak muscle activation remained unchanged or decreased, and spinal loading (compression and anterior-posterior shear) decreased when the extension exercises were performed on the ball. The lumbar spine postures attained during the exercises did not differ between surfaces. CONCLUSIONS: The assumption that the use of an exercise ball will always create a greater challenge for the musculoskeletal system was not supported by the findings of this study. Likewise, in a healthy, young population, there does not appear to be any training advantage to performing extensor exercises on a ball versus a mat. However, in a rehabilitation scenario, these exercises performed on a ball could reduce low back loading and hence reduce the potential for reinjury.

Abdominal Muscles↗

PubMed2006

Stability ball versus office chair: comparison of muscle activation and lumbar spine posture during prolonged sitting.

OBJECTIVE: The objective of the study was to evaluate the differences between sitting on a stability ball and in an office chair in terms of trunk muscle activation and lumbar spine posture. BACKGROUND: Stability balls have become increasingly popular as an alternative to office chairs to help reduce the prevalence of low back pain; however, little research has been conducted on their use as office chairs. METHODS: The 14 participants (7 men, 7 women) were required to sit on both a stability ball and an office chair for 1 hour each while performing various computer workstation tasks throughout the sitting periods. The activation of eight muscles and lumbar spine posture were measured and analyzed. RESULTS: Increased muscle activation in thoracic erector spinae (p = .0352), decreased pelvic tilt (p = .0114), and increased perceived discomfort (p < .0001) while sitting on the stability ball were observed. CONCLUSIONS: The small changes in biological responses when sitting on a stability ball as compared with an office chair, combined with the increased reported discomfort while on the ball, suggests its use for prolonged sitting may not be advantageous. APPLICATION: Prolonged sitting on a stability ball does not greatly alter the manner in which an individual sits, yet it appears to increase the level of discomfort. Therefore, it is important to fully explore a new chair design and consult scientific research before implementing its use.

Adult↗

PubMed2005

Estimating the compressive strength of the porcine cervical spine: an examination of the utility of DXA.

STUDY DESIGN: The failure strength of porcine spinal units was correlated with vertebral size and bone mineralization. The accuracy of the resulting predictive equations was tested with an independent sample of spinal units. OBJECTIVES: To determine if dual energy x-ray absorptiometry (DXA)-obtained measures of bone mineralization can be used to accurately predict the compressive tolerance of porcine spinal units. SUMMARY OF BACKGROUND DATA: Porcine spinal units are often used in place of cadaveric tissues, and normalization is used to improve the transferability of model results. In compressive testing, normalization can be performed to the estimated compressive strength. Bone mineralization measures have been shown to be positively correlated with compressive tolerance and have been used to predict the tolerance of human spinal units. However, the accuracy of these predictive equations has not been assessed with an independent sample. METHODS: Twenty porcine cervical spinal units were scanned (DXA) to obtain measures of bone mineral content (BMC) and bone mineral density (BMD). The units were compressed to failure, and the failure loads were correlated with the measured bone mineralization and endplate area of the spinal unit. The regression equations were used to predict the compressive tolerance of an independent sample of spinal units. RESULTS: BMC (P = 0.078) and BMD (P = 0.2834) were not significantly correlated to compressive strength. Endplate area was the most highly correlated variable, with an r of 0.5329. The use of a predictive equation including BMC on the second independent sample resulted in errors of estimation of 1.4 +/- 1.2 kN, corresponding to 13% of the average compressive strength. In comparison, the use of an equation employing endplate area alone resulted in estimation errors of 11%. CONCLUSIONS: Measures of BMC/BMD did not enhance predictions of compressive strength and will not reduce errors in compressive load normalization in a porcine model. The poor correlations found between BMC and compressive strength may be due to the non-load-bearing anterior processes of the porcine cervical spine.

Absorptiometry, Photon↗

PubMed2005

Elimination of electrocardiogram contamination from electromyogram signals: An evaluation of currently used removal techniques.

Trunk electromyographic signals (EMG) are often contaminated with heart muscle electrical activity (ECG) due to the proximity of the collection sites to the heart and the volume conduction characteristics of the ECG through the torso. Few studies have quantified ECG removal techniques relative to an uncontaminated EMG signal (gold standard or criterion measure), or made direct comparisons between different methods for a given set of data. Understanding the impacts of both untreated contaminated EMG and ECG elimination techniques on the amplitude and frequency parameters is vital given the widespread use of EMG. The purpose of this study was to evaluate four groups of current and commonly used techniques for the removal of ECG contamination from EMG signals. ECG recordings at two intensity levels (rest and 50% maximum predicted heart rate) were superimposed on 11 uncontaminated biceps brachii EMG signals (rest, 7 isometric and 3 isoinertial levels). The 23 removal methods used were high pass digital filtering (finite impulse response (FIR) using a Hamming window, and fourth-order Butterworth (BW) filter) at five cutoff frequencies (20, 30, 40, 50, and 60 Hz), template techniques (template subtraction and an amplitude gating template), combinations of the subtraction template and high pass digital filtering, and a frequency subtraction/signal reconstruction method. For muscle activation levels between 10% and 25% of maximum voluntary contraction, the template subtraction and BW filter with a 30 Hz cutoff were the two best methods for maximal ECG removal with minimal EMG distortion. The BW filter with a 30 Hz cutoff provided the optimal balance between ease of implementation, time investment, and performance across all contractions and heart rate levels for the EMG levels evaluated in this study.

Adult↗

PubMed2005

Gender-based differences in postural responses to seated exposures.

BACKGROUND: Individuals may respond differently to various chair designs and the factors that influence these sitting behaviours are not well understood. There is very little information in the scientific literature regarding the observation and documentation of gender differences in seated postures. In particular, anecdotal observations of potential gender-specific sitting behaviours led us to test the influence of gender on the postural responses to different seated conditions. METHODS: Sixteen healthy university students (8 males and 8 females) were tested on four different chair configurations. Upper body kinematics (spine angles and centre of mass) and seat pressure profiles (centre of pressure, peak pressure) were obtained during each testing session. FINDINGS: Regardless of the chair used or the task performed, average lumbar and trunk angles were significantly more flexed for males than for females (P=0.047 and P=0.0026, respectively). Males exhibited average lumbar spine and trunk angles of 65.4 degrees (SD 16.2 degrees ) and 29.8 degrees (SD 28.3 degrees ), respectively, while female lumbar spine and trunk angles were 49.6 degrees (SD 23.1 degrees ) and -3.3 degrees (SD 20.4 degrees ), respectively. The pelvis was posteriorly rotated for males (7.6 degrees (SD 8.2 degrees )) and anteriorly rotated for females (-5.5 degrees (SD 9.3 degrees )) (P=0.0008). Significant gender *chair interactions of the location of the individual on the chair seat were most marked for the pivoting chair with a back rest. Females positioned their centre of mass and hip joints anterior to the chair pivot point while males' centre of mass (P=0.0003) and hip joints (P=0.0039) were located posterior to the pivot point. Females also sat with their centre of mass closer to the seat pan centre of pressure than males when a back rest was present (P=0.0012). INTERPRETATION: Males and females may be exposed to different loading patterns during prolonged sitting and may experience different pain generating pathways. Therefore, gender-dependent treatment modalities and/or coaching should be implemented when considering methods of reducing the risk of injury or aggravation of an existing injury.

Abdomen↗

PubMed2005

The influence of static axial torque in combined loading on intervertebral joint failure mechanics using a porcine model.

BACKGROUND: The spine is routinely subjected to repetitive combined loading, including axial torque. Repetitive flexion-extension motions with low magnitude compressive forces have been shown to be an effective mechanism for causing disc herniations. The addition of axial torque to the efficacy of failure mechanisms, such as disc herniation, need to be quantified. The purpose of this study was to determine the role of static axial torque on the failure mechanics of the intervertebral joint under repetitive combined loading. METHODS: Repetitive flexion-extension motions combined with 1472 N of compression were applied to two groups of nine porcine motion segments. Five Nm of axial torque was applied to one group. Load-displacement behaviour was quantified, and planar radiography was used to document tracking of the nucleus pulposus and to identify fractures. FINDINGS: The occurrence of facet fractures was found to be higher (P=0.028) in the axial torque group (7/9), compared to the no axial torque group (2/9). More hysteresis energy was lost up to 3000 cycles of loading in the axial torque group (P<0.014). The flexion-extension cycle stiffness was not different between the two groups until 4000 cycles of loading, after which the axial torque group stiffness increased (P=0.016). The percentage of specimens that herniated after 3000 cycles of loading was significantly larger (P=0.049) for the axial torque group (71%) compared to the no axial torque group (29%). INTERPRETATION: Small magnitudes of static axial torque alter the failure mechanics of the intervertebral disc and vertebrae in combined loading situations. Axial torque appears to accelerate the susceptibility for injury to the intervertebral joint complex. This suggests tasks involving axial torque with other types of loading, apart from axial twist motion, should be monitored to assess exposure and injury risk.

Animals↗

PubMed2005

Effects of minimum sampling rate and signal reconstruction on surface electromyographic signals.

Signal oversampling is frequently used to prevent distortion in time-series representations. When sampling at rates just above the Nyquist critical frequency (f(c)), Shannon's reconstruction theorem provides an alternative means of circumventing this problem. The purpose of this study was to determine whether surface electromyographic (EMG) data is compromised when sampled just above f(c) and whether Shannon's reconstruction theorem can correct these deficiencies, if present. Brief isometric elbow flexion contractions were performed at 100%, 80%, 50%, 25%, 10%, 5% and 2.5% maximum voluntary contraction (MVC) followed by one trial of random cyclic isometric contractions and relaxations. The 2kHz signal was resampled at 1kHz and the 2 and 1kHz signals were reconstructed (2RS and 1RS, respectively) to a sampling rate of 20kHz. Data were full-wave rectified (FWR) and low-pass filtered (LE). Peak amplitudes of the FWR and LE signals, average EMG (AEMG) amplitudes of the FWR and LE signals, mean power frequency of the raw data, number of gaps, and mean gap time of the LE signals were calculated. Significant differences were present in peak EMG and AEMG measurements between the 1 and 2kHz, 2RS and 20kHz signals and occasionally between the 1RS and the 2kHz, 2RS and 20kHz signals. These differences, although statistically significant were quite small amounting to less than 0.5% MVC. No significant differences were found for the gaps parameters. The small differences seen, coupled with the processing time required for signal reconstruction, make oversampling as well as signal reconstruction in surface EMG measurements unnecessary.

Adult↗

PubMed2004

The effect of static torsion on the compressive strength of the spine: an in vitro analysis using a porcine spine model.

STUDY DESIGN: Matched porcine cervical spine motion segments were subjected to two main conditions and compared: axial compression and axial compression combined with varying axial torque. OBJECTIVES: To determine the effect of torsion on the acute compressive strength of the spine. SUMMARY OF BACKGROUND DATA: The spine is often subjected to compression together with axial torque as a component of complex loading, yet there is a lack of documentation on its effect on the compressive strength and injury mechanics. METHODS: Matched cohorts of porcine cervical spine (C5-C6) motion segments were compressed to failure at a rate of 3,000 N/s combined with 0 Nm, 5 Nm, 20 Nm, or 30 Nm of axial torque. Three "failure" points were recorded from the stress/strain association: the first "step" (initial microfracture), the initial slope change (yield point or "slow crush" mechanism), and the ultimate failure point (fracture). Furthermore, resultant injuries were documented using planar radiography and visual inspection following dissection of the motion segments. RESULTS: Axial torque affected the failure characteristics during acute compressive loading. The ultimate strength of the motion segments was significantly reduced with increasing static torques. The compressive load at which initial microfracture occurred, indicated by the first "step" in the load-deformation curve, was increased with 5 Nm, 10 Nm, and 20 Nm of applied torsion in comparison to no torque, but this effect was reduced with 30 Nm of torque. The "slow crush" mechanism of failure was not affected by the addition of axial torque. No radiographic gross injuries to the facet joints were observed. Damage appeared to be confined to the endplate and trabecular network of the vertebral body. CONCLUSIONS: Based on this animal model, shown to have similar biomechanical behavior to humans, axial torque appears to significantly reduce the compressive strength of the spine.

Animals↗

PubMed2004

The time-varying response of the in vivo lumbar spine to dynamic repetitive flexion.

OBJECTIVE: To quantify the time-varying stiffness and kinematic responses of the in vivo lumbar spine exposed to dynamic repetitive flexion movements. DESIGN: Changes in in vivo passive lumbar moment-angle relationships were monitored in response to dynamic repetitive flexion. BACKGROUND: While previous in vitro studies have provided conflicting evidence on the effects of repetitive flexion movements on the stiffness of the lumbar spine, no previous studies have quantified the time-varying changes of the in vivo lumbar spine to dynamic repetitive flexion. METHODS: Subjects lifted and lowered a 4.5 kg load over two barriers at a rate of 7 lifts per minute for 1.5 h inducing at least 80% of the lumbar flexion range of motion. Prior to lifting and at 30 min intervals passive moment-angle relationships were obtained by pulling the subject into flexion on a customized frictionless table. RESULTS: Repetitive lifting induced a decreasing stiffness trend after 30 min, followed by a recovery towards initial stiffness levels with further loading. The trends were non-significant for all measures studied. CONCLUSIONS: The results indicate that after 30 min of lifting, creep within the passive tissues may allow workers to exceed their initial range of motion, altering joint mechanics and loading patterns potentially leading to an increased risk of developing low back pain. RELEVANCE: Given the potential for time-varying changes to alter the spine's risk of injury and injury mechanisms, knowledge regarding the stiffness response of the in vivo lumbar spine exposed to repetitive flexion may lead to improved understanding and prevention of work related back pain.

Adaptation, Physiological↗

PubMed2004

The reliability of quantifying upright standing postures as a baseline diagnostic clinical tool.

OBJECTIVE: To assess the reliability of posture across and within subjects, specifically the repeatability of spinal angles determined by digitization of images in the anterior, posterior, and sagittal views. DESIGN: A repeated measure design was used in which subjects were required to attend 3 sessions, each consisting of 3 trials. Photographs of the anterior, posterior, and lateral views of normal, relaxed upright standing were taken during each trial. Landmarks were digitized and cervical, thoracic, and lumbar angles were calculated with respect to a vertical reference line. SUBJECTS: Fourteen healthy and active subjects (7 male subjects and 7 female subjects) were recruited from a university student population. All had been free of low back pain during the previous 6 months. RESULTS: When comparing mean angles, no significant differences were detected for any angle in any view. However, large variability within subjects was observed, likely leading to the lack of significance found with respect to the main factors in the analysis of variance (ANOVA). Large coefficients of variance (CVs) reflect the substantial intrasubject variability, as well as poor to moderate agreement indicated by intraclass correlation coefficients (ICCs). There were no apparent trends indicating that gender affected repeatability of posture. CONCLUSIONS: The poor repeatability of postures documented using the studied method brings into question the validity of this postural analysis approach for either diagnostic use or tracking changes in response to treatment. Users of such postural analysis tools should interpret postural deviations from a vertical reference with caution, as there are many inherent factors that can contribute to the variability of these measured postures.

Adult↗

PubMed2003

The effects of a continuous passive motion device on myoelectric activity of the erector spinae during prolonged sitting at a computer workstation.

Continuous passive motion (CPM) has been proposed as a method to help individuals with low back pain cope with prolonged sitting. The purpose of this study was to investigate the effects that a commercially available CPM device had on lumbar and thoracic erector spinae (ES) muscle activation (using surface electromyography, "EMG"), and on subjective discomfort during prolonged seated computer work with and without the use of the CPM device. There were no significant differences in average ES muscle activation levels, amplitude probability distribution functions, and EMG gaps number and length when sitting with the CPM device was compared to sitting normally. Subjective ratings of discomfort were also not significantly different between the two sitting conditions. The results indicated that there were no clear mechanisms by which the CPM device may reduce ES muscle pain and fatigue for the tasks and pain-free individuals studied.

Adult↗

PubMed2002

Inter- and intra-observer reliability of calculating cumulative lumbar spine loads.

The aim of this study was to quantify the precision of manual video digitization of three typical industrial tasks, as evaluated by the comparison of four cumulative kinetic parameters at the L4/L5 intervertebral joint: compression, joint shear, reaction shear and moment. Ten observers were recruited (five male and five female), with an undergraduate background in human anatomy. On each of three test days, each observer digitized five repeats of each of three typical industrial lifting tasks of 5 to 6 s in duration. A rigid link segment model that incorporated a single muscle equivalent model was used to calculate the cumulative loading based on the digitized coordinates. Inter-observer reliability was assessed using a mixed model ANOVA, and no significant differences were found to result from observer, gender, day or trial. Intraclass correlation coefficients (ICC) were calculated within each task to quantify intra-observer reliability. Overall, the ICCs were excellent (>0.75), with the exception of moderate values for reaction shear for Tasks 2 and 3. Compression and moment demonstrated the highest reliability of the four parameters studied, which is beneficial from an ergonomic standpoint, as compression is the most commonly used parameter for job assessments. This study demonstrated manual video digitization to be a reliable tool for the quantification of cumulative spinal loading, both within a given observer, and across days, trials and observers.

Adult↗

PubMed2002

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.

Adult↗

PubMed1997

Dynamic loading affects the mechanical properties and failure site of porcine spines.

OBJECTIVE: The purpose of this study was to investigate the effect of load rate on the mechanical characteristics of spinal motion segments under compressive loading. DESIGN: An in vitro experiment using a porcine model which ensured a homogeneous population for age, weight, genetic background and physical activity. BACKGROUND: Spinal motion segments comprise of viscoelastic materials, and as a result the rate of loading will modulate mechanical characteristics and fracture patterns of the segments. METHODS: Twenty-six cervical porcine spines were excised immediately post-mortem with all soft tissue intact. Spines were then separated into two specimens each consisting of three vertebral bodies and the two intervening intervertebral discs (C2-C4 and C5-C7) and loaded to failure under five loading rates (100, 1000, 3000, 10 000 and 16 000 N s(-1)). After the specimens failed, they were dissected to determine the mode of failure. RESULTS: Dynamic loading increases the ultimate load compared with quasi-static loading (100 N s(-1)), whereas the magnitude of dynamic loading (1000-16 000 N s(-1)) appears not to have a significant affect. Stiffness behaved in a similar manner. The displacement to failure of specimens decreased as load rate increased, although there was a diminishing effect at high load rates. Furthermore, failure at low load rates occurred exclusively in the endplate, whereas failure of the vertebral body appeared with greater frequency at higher load rates. CONCLUSIONS: The mechanical characteristics and resulting injuries of porcine spinal motion segments were affected as the loading rates changed from quasi-static to dynamic. The modulating factors of the mechanical characteristics of the spine need to be understood if valid models are to be designed which will increase the understanding of spinal function, and are important for choosing better injury prevention and rehabilitation programmes.

Journal Article↗

PubMedDate not supplied

Implications for the use of postural analysis as a clinical diagnostic tool: reliability of quantifying upright standing spinal postures from photographic images.

OBJECTIVES: A repeated measures design was used to test the reliability of standing spine postures within subjects using a biologically relevant measure determined by digitization of images and to compare the results to a previously tested vertical reference method. METHODS: Twenty subjects attended 3 sessions consisting of 5 trials each. Photographs of the sagittal and posterior views of normal upright standing were taken. Landmarks were digitized and cervical, thoracic, and lumbar spinal angles were calculated using the algebraic dot product. Intraclass correlation coefficients were used to evaluate intrasubject reliability across sessions. RESULTS: According to the intraclass correlation coefficients, posture had good to excellent reliability in the sagittal view and provided a more stable measure of spinal angles than the posterior view. Mean repositioning errors were less than 6 degrees and 2 degrees in the sagittal and posterior views, respectively. CONCLUSIONS: Although the repeatability of posture was improved in the sagittal view, when a biological measure was used instead of an external vertical reference to calculate spinal angles, individual subject posture was still variable. This brings into question the effectiveness and validity of using surface skin markers to track postural changes due to clinical interventions. If the postural analysis approach is to be used to detect changes due to clinical treatment, such changes must be larger than the baseline repositioning errors seen in healthy subjects.

Adult↗

PubMedDate not supplied

Effects of prolonged sitting on the passive flexion stiffness of the in vivo lumbar spine.

BACKGROUND CONTEXT: Prolonged sitting may alter the passive stiffness of the lumbar spine. Consequently, performing full lumbar flexion movements after extended periods of sitting may increase the risk of low back injury. PURPOSE: The purpose was to quantify time-varying changes in the passive flexion stiffness of the lumbar spine with exposure to prolonged sitting and to link these changes to lumbar postures and trunk extensor muscle activation while sitting. A secondary objective was to determine whether men and women responded differently to prolonged sitting. STUDY DESIGN: Passive lumbar flexion moment-angle curves were generated before, during and after 2 hours of sitting. Lumbar flexion/extension postures and extensor muscle activation levels were measured while sitting. SAMPLE: Twelve (6 men, 6 women) university students with no recent low back pain were studied. OUTCOME MEASURES: Quantified changes in the shapes of the passive flexion moment-angle curves (slopes, breakpoints and maximum lumbar flexion angles) were the outcome measures. While sitting, average lumbar flexion/extension angles, the distribution of lumbar flexion/extension postures, average electromyogram (EMG) amplitude, the number and average length of EMG gaps, and trunk extensor muscle rest levels were measured. METHODS: Participants performed deskwork for 2 hours while sitting on the seat pan of an office chair. Moment-angle relationships for the lumbar spine were derived by pulling participants through their full voluntary range of lumbar flexion on a customized frictionless table. RESULTS: Lumbar spine stiffness increased in men after only 1 hour of sitting, whereas the responses of women were variable over the 2-hour trial. Men appeared to compensate for this increase in stiffness by assuming less lumbar flexion in the second hour of sitting. CONCLUSIONS: Changes in the passive flexion stiffness of the lumbar spine may increase the risk of low back injury after prolonged sitting and may contribute to low back pain in sitting.

Adult↗