Clive D'Souza

Creep and fatigue development in the low back in static flexion.

Study Design. In vivo measurements of low back flexion posture and muscle activity before, during, and after static flexion. Objective. To identify the occurrence of creep and muscle fatigue development in the low back during static upper body deep flexion that resembled an above ground work posture. Summary of Background Data. Static lumbar flexion has been related to the development of low back disorders, and its injury mechanism has been focused on the changes in passive spinal tissues. Potential influences of muscle fatigue of extensor muscles have not been explored. Methods. A total of 20 asymptomatic subjects performed submaximal isometric trunk extension exertions and an isokinetic trunk flexion before and immediately after 5-minute static flexion while the trunk sagittal flexion angle and the myoelectric activities (electromyography [EMG]) of back extensor muscles were recorded simultaneously. Changes in the flexion-relaxation onset angle, maximum flexion angle, muscle activity level, and the median power frequency of EMG associated with the static flexion were evaluated. Results. Flexion-relaxation onset angle in isokinetic flexion and EMG amplitude of isometric extension were significantly greater after static flexion, indicating creep of spinal tissues in static flexion. Median power frequency of lumbar erector spinae EMG during isometric extension was significantly lower after static flexion, suggesting the development of muscle fatigue. Consistent but low level of EMG was observed together with sporadic muscle spasms during the static flexion period. Conclusion. Fatigue of low back extensor muscles may occur in static flexion due to prolonged passive stretching of the muscles. Low back extensor muscles are required to generate more active forces in weight holding or lifting after static flexion to compensate for the reduced contribution of creep deformed passive tissues in maintaining spinal stability and the posture. The degraded force generating capacity of the fatigued muscles can be a significant risk factor for low back pain.

Anthropometry and Standards for Wheeled Mobility: An International Comparison

ABSTRACT Space requirements for accommodating wheeled mobility devices and their users in the built environment are key components of standards for accessible design. These requirements typically include dimensions for clear floor areas, maneuvering clearances, seat and knee clearance heights, as well as some reference dimensions on wheeled mobility device sizes. Recent research from four countries was reviewed and compared with their prevailing accessibility standards to identify needs for improving standards. Findings from ongoing anthropometry research on wheeled mobility in the U.S. were used for evaluating the adequacy of existing U.S. accessibility standards. Preliminary analysis suggests that the U.S. standards, which are based on research conducted in the 1970s, need to be updated to address advances in wheeled mobility technology and changes in user demographics. The analysis highlights the importance of integrating research with standards development, organizing international collaborations, and developing international standards.

Changes in the EMG of Low Back Muscles during Static Lumbar Flexion

Prolonged and/or frequent lumbar flexion posture in industry has been known to contribute to the development of work-related low back pain or disorders but the specific biomechanics of this link has not been fully developed. In this study the effects of static lumbar flexion on back extensor muscles were evaluated by quantifying the changes in the flexion-relaxation onset angle, muscle activity level and the development of muscle fatigue associated with static lumbar flexion. Twenty healthy subjects performed submaximal isometric trunk extension exertions and isokinetic trunk flexion before and immediately after a 5 min continuous lumbar flexion posture while the trunk sagittal flexion angle and the myoelectric activities (EMG) of erector spinae muscles and latissimus dorsi muscles were recorded simultaneously. Results show an increase in the flexion-relaxation onset angle, normalized EMG of isometric extension, and decrease in the median power frequency of EMG as a consequence of the static lumbar flexion. It is suggested that back extensor muscles produce sustained low level contraction during static lumbar flexion, leading to muscular fatigue development. Together with creep deformed passive tissues of the low back and resultant spinal instability, the muscle fatigue of back extensors in static lumbar flexion may play a role in the development of low back pain or disorders.