Marianne Magnusson

Muscular Response to Sudden Load: A Tool to Evaluate Fatigue and Rehabilitation

Study Design Subjects were exposed to fatiguing and restorative interventions to assess their response to sudden loads. Objectives To investigate the erector spinae and rectus abdominis response characteristics to “sudden load” and the effect of fatigue and rehabilitation. Summary of Background Data Unexpected loads, which people often experience, can lead to high forces in the spine and may be a cause of low back injury. Methods Muscle responses to sudden load were mediated by fatigue, walking, expectation, method of load application, exposure to vibration, and cognitive‐behavioral rehabilitation in patients with chronic low back pain. A novel technique, perfected in this work, called wavelet analysis, was used to analyze these data. Results Reaction time was affected by fatigue and expectation. Vibration exposure significantly increased the muscle response time. Walking was able to ameliorate that effect. Back muscles responded differently, depending on whether loads were applied to the back through the hands or through the trunk. Electromyographic reaction time and magnitude decreased in patients after a 2‐week rehabilitation program. Conclusions Sudden loads can exacerbate fatigue effects. Walking after driving reduces the risk to the back caused by handling unpredictable loads. Vibration exposure guidelines should be more conservative. Patients have longer response times than healthy subjects, but patients can improve their response to sudden loads via rehabilitation. Patients exhibit a flexion‐extension oscillation at 5 Hz in response to a sudden load, suggesting that the 5‐Hz, seated, natural frequency observed during whole‐body vibration may result from neurophysiologic control limits.

Are occupational drivers at an increased risk for developing musculoskeletal disorders

Study Design This study analyzed the role of exposure to driving and other covariates in reports of back, neck, and shoulder pain and resultant disability. Cohorts in Sweden and the United States were compared. Objectives To establish the effect of mechanical and psychosocial factors in reporting back, neck, and shoulder pain and work loss. Summary of Background Data There are numerous reports of a positive relationship between back pain and driving. However, exposure data are minimal. The influence of job satisfaction has not been assessed. Methods The physical factors affecting reports of back, neck, and shoulder pain were investigated in a two‐country cohort study of bus and truck drivers and sedentary workers. Vibration exposure was obtained by directly measuring the vibration imposed on the driver during a typical work day. Lifting exposure was attained by questionnaire. Cumulative exposure was computed based on work history. Musculoskeletal health information was based on a modified nordic questionnaire, and other questionnaires recorded the physical and psychosocial aspects of the work environment. Results Of the sample, 50% reported low back pain, with no difference between countries. The highest risk factors (odds ratios) for back and neck pain were long‐term vibration exposure, heavy lifting, and frequent lifting. A combination of long‐term vibration exposure and frequent lifting carried the highest risk of low back pain. Work loss from low back pain was influenced by perceived job stress. Conclusions Vibration (resulting from driving) and lifting cause back, neck, and shoulder pain, whereas inability to work seems affected by stress at work.

Transmissibility of 15-Hertz to 35-Hertz Vibrations to the Human Hip and Lumbar Spine: Determining the Physiologic Feasibility of Delivering Low-Level Anabolic Mechanical Stimuli to Skeletal Regions at Greatest Risk of Fracture Because of Osteoporosis

Study Design. Experiments were undertaken to determine the degree to which high-frequency (15–35 Hz) ground-based, whole-body vibration are transmitted to the proximal femur and lumbar vertebrae of the standing human. Objectives. To establish if extremely low-level (<1 g, where 1 g = earth’s gravitational field, or 9.8 ms−2) mechanical stimuli can be efficiently delivered to the axial skeleton of a human. Summary of Background Data. Vibration is most often considered an etiologic factor in low back pain as well as several other musculoskeletal and neurovestibular complications, but recent in vivo experiments in animals indicates that extremely low-level mechanical signals delivered to bone in the frequency range of 15 to 60 Hz can be strongly anabolic. If these mechanical signals can be effectively and noninvasively transmitted in the standing human to reach those sites of the skeleton at greatest risk of osteoporosis, such as the hip and lumbar spine, then vibration could be used as a unique, nonpharmacologic intervention to prevent or reverse bone loss. Materials and Methods. Under sterile conditions and local anesthesia, transcutaneous pins were placed in the spinous process of L4 and the greater trochanter of the femur of six volunteers. Each subject stood on an oscillating platform and data were collected from accelerometers fixed to the pins while a vibration platform provided sinusoidal loading at discrete frequencies from 15 to 35 Hz, with accelerations ranging up to 1 gpeak-peak. Results. With the subjects standing erect, transmissibility at the hip exceeded 100% for loading frequencies less than 20 Hz, indicating a resonance. However, at frequencies more than 25 Hz, transmissibility decreased to approximately 80% at the hip and spine. In relaxed stance, transmissibility decreased to 60%. With 20-degree knee flexion, transmissibility was reduced even further to approximately 30%. A phase-lag reached as high as 70 degrees in the hip and spine signals. Conclusions. These data indicate that extremely low-level, high-frequency mechanical accelerations are readily transmitted into the lower appendicular and axial skeleton of the standing individual. Considering the anabolic potential of exceedingly low-level mechanical signals in this frequency range, this study represents a key step in the development of a biomechanically based treatment for osteoporosis.

Psychological and physiological stress responses during repetitive work at an assembly line

Abstract The association between psychological and physiological stress responses was examined in 20 male workers at an assembly line. Each worker was studied during a 2 h period on two consecutive days in their normal job and, in order to obtain physiological baseline values, during a corresponding paid 2 h period off the job on the third day. Self-reports of work demands, mood, etc., measurements of catecholamine and cortisol excretion and of systolic and diastolic blood pressure and heart rate were obtained at the end of each of the three 2 h periods. Work induced a significant elevation in almost all psychological and physiological measurements. Levels were consistently lower in workers reporting a ‘good’ workday compared to those reporting a ‘normal’ or a ‘bad’ day. Correlations between self-reports and physiological values showed that catecholamine and cortisol responses, respectively, tended to be associated selectively with different psychological conditions, catecholamine values being associated ...

Low Back Pain and Whole Body Vibration

The investigators describe their multifaceted approach to the study of the relationship between whole body vibration and low back pain. The epidemiologic study was a two center study of drivers and sedentary workers in the United States and Sweden. The vibration exposure was measured in the vehicles. It was found that the career vibration exposure was related to low back, neck, and shoulder pain. However, disability was related to job satisfaction. In vivo experiments, using percutaneous pin mounted accelerometers have shown that the natural frequency is at 4.5 Hz. The frequency response is affected by posture, seating, and seat back inclination. The response appears to be determined largely by the rocking of the pelvis. Electromyographic studies have shown that muscle fatigue occurs under whole body vibration. After whole body vibration exposure the muscle response to a sudden load has greater latency. Vehicle driving may be a reason for low back pain or herniated nucleus pulposus. Prolonged seating exposure, coupled with the whole body vibration, should be reduced for those recovering from these problems. Vibration attenuating seats and correct ergonomic layout of the cabs may reduce the risks of recurrence.

Postural changes of the dural sac in the lumbar spines of asymptomatic individuals using positional stand-up magnetic resonance imaging.

Study Design. Positional magnetic resonance imaging (MRI) study of control subjects. Objectives. To determine dimensional changes in the lumbar dural sac as a function of posture, and to establish changes between the supine, erect and seated positions. Summary of Background Data. Studies using computerized tomography and MRI were done to determine the mechanical effects on the lumbar spinal canal in the different positions. There has been no consecutive study, however, in which normal individuals were investigated for positional changes of the dural sac, including true standing position. Methods. Thirty-two male asymptomatic volunteers were recruited. The examination was performed using a new MRI system. All subjects were examined with sagittal T2 and axial T1-weighted spin-echo images. The subjects were studied in the supine, standing, and sitting positions. The measurements were made using OSIRIS software (Digital Imaging Unit University Hospital of Geneva, Geneva, Switzerland). On axial images, dural sac cross-sectional area and anteroposterior (AP) dural sac diameter were measured at the level of the L3/4, L4/5, and L5/S1 discs. On midsagittal images, AP dural sac diameter and the upper-endplate angles of L1 and S1 were measured. Results. We found a disc degeneration or disc protrusion in 41% (12/29) of the subjects, but there was no obvious compression of the dural sac. Depending on the postures, the mean dural sac cross-sectional area and AP dural sac diameter changed. At all levels, mean dural sac cross-sectional area in the supine position was significantly smaller than in other postures. The dural area decreased most at the L5/S1 level due to positional change from standing to supine. The largest dural area at the L5/S1 level was in sitting extended. AP dural sac diameter on axial and midsagittal images showed a similar tendency. Conclusions. A significant posture-dependent difference of the dural sac cross-sectional area at the level of intervertebral disc in asymptomatic volunteers has been demonstrated. When the posture changed from supine to standing position, lumbar dural sac volume expanded by the increased pressure of cerebrospinal fluid, and the dural sac cross-sectional area increased. The smallest values were found in the supine position.

Measurement of height loss during whole body vibrations.

An experimental, in vivo study was performed to measure height changes in subjects exposed to whole body vibrations while seated. Twelve women, with an average age of 22 years, were exposed to sinusoidal vibrations for 5 mins. The vibration frequency was 5 Hz, and the acceleration was 0.1 g Rms. The height loss stemming from vibration exposure was compared with that experienced while sitting without being subjected to vibrations. The height losses that always occurred from the two exposures were corrected for the effect of posture change. The height loss from vibration was significantly greater than when no vibration was present. Height loss due to posture change was responsible for approximately 50% of the total height loss. From this study it was concluded that whole body vibrations cause increased height loss.

Motor control learning in chronic low back pain.

Study Design. A randomized prospective cohort study of participants with chronic low back pain, seeking physical therapy, with follow-up at weeks 6 and 28. Effects of conventional physiotherapy and physiotherapy with the addition of postural biofeedback were compared. Objective. To evaluate the benefits of postural biofeedback in chronic low back pain participants. Summary of Background Data. Biofeedback using electromyographic signals has been used in chronic low back pain with mixed results. Postural feedback had not been previously used. Methods. Demographic and psychological baseline data along with range of motion were analyzed from a sample of 47 chronic participants with low back pain randomized into conventional physiotherapy with or without the addition of postural biofeedback. Results. After 6 months, there were 21 dropouts. The participants with biofeedback had markedly improved status in visual analog pain scales, short form-36, and range of motion. Conclusion. The study strongly suggests that postural feedback is a useful adjunct to conventional physiotherapy of chronic low back pain participants.

The loads on the lumbar spine during work at an assembly line. The risks for fatigue injuries of vertebral bodies.

This study was performed in an attempt to determine the total spinal compressive load during assembly line work to find a possible association with the many complaints of back pain. A flexion analyzer was used to register trunk movements, and analysis of postures and lifted weights was done from video recordings. The load on the spine at the L3 level was calculated through a biomechanical model, meant for analysis of static, sagittally symmetric postures and lifting tasks. Maximum lift tests were performed before and after a full work day. The peak load on the L3–L4 level when lifting corresponded to an average 22% of the load at the lift test. The mean load during a work cycle was 818 N. It was concluded that the many complaints of back pain could not be attributed to high peak loads, repetitivity of the lifts, or large load doses. Monotony, stress, and low job satisfaction are more likely factors of greater importance.

The effect of seat back inclination on spine height changes

The effect of backrest inclination on spinal height changes was tested during static sitting and seated whole-body vibrations. The vibration input was sinusoidal with a frequency of 5 Hz and an acceleration of 0.1 g rms. The backrest inclinations tested were 110 degrees and 120 degrees . The 110 degrees backrest caused less shrinkage than did the 120 degrees during static sitting, whereas the opposite was true when vibration was present, although the differences between the backrests were not statistically significant. Only when the results were compared with results from exposure to unsupported sitting were the differences statistically significant for both static sitting and seated vibrations when the 110 degrees backrest was used and for vibration with the 120 degrees backrest. Thus we conclude that an inclined backrest reduces the effects of vibration. More importantly, emphasis should be placed upon seats and seat materials that can attenuate vibration.