Work-related low back disorders (WRLBDs) are common and costly in the U.S. and numerous interventions aiming to reduce WRLBD risk have been developed.  In one approach, training programs incorporating the work strategies (or work methods) of experienced workers have often been proposed as a training model or a behavior target of training.  However, both the specific role of work experience in contributing to WRLBDs and the effectiveness of such an intervention approach are not well understood.  In the current research, differential work strategies of experienced workers and associated WRLBD risk were identified, in the context of several common occupational activities.  Three experiments were completed, in which both experienced workers and matched novices participated.  These experiments involved relatively short duration repetitive lifts/lowers, more prolonged lifts/lowers that induced fatigue, and dynamic pushes/pulls.  Diverse aspects of work strategies were quantified, emphasizing torso kinematics/kinetics, balance maintenance, and/or torso movement stability.  During short-term repetitive lifts/lowers, experienced workers exhibited higher torso kinematics and kinetics, suggestive of a higher risk for WRLBDs, though better balance maintenance and torso stability were evident in this group.  Thus, experienced workers may trade off an increased risk for WRLBDs to achieve better balance and torso stability.  Fatigue modified work methods during repetitive lifts/lowers in both the novice and experienced groups, though the associated contribution to WRLBDs was unclear due to opposite changes in torso kinematics vs. kinetics.  More consistently, fatigue decreased balance maintenance during lifts/lowers.  Fatigue also modified work methods adopted by experienced workers, leading to higher torso kinetics, that were suggestive of a higher risk for WRLBDs during lifts/lowers.  For dynamic pushes/pulls, experienced workers used lower torso kinematics and kinetics, suggestive of a lower risk for WRLBDs.  As a whole, these results suggest that work methods are distinct between novices and experienced workers.  Further, work experience may not consistently reduce WRLBD risk, and the influences of experience may be task specific.  Such findings can help guide the development of future interventions, particularly training, targeting the control of WRLBDs. / Ph. D.

The stability of the spine can be estimated from kinematic variability and nonlinear analyses of seated balance tasks. However, processing methods require sufficient signal duration and test-retest experiments require that the assessment must be reliable. Our goal was to characterize the reliability and establish the trial duration for spine stability assessment. Stationarity, kinematic variability and nonlinear dynamic stability were quantified from kinetic and kinematic data collected during balance performance. Stationarity results showed that a minimum 30 seconds test duration is necessary. Intra-session reliability was excellent, however inter-session reliability needed more test trials to achieve excellent reliability. Few studies have investigated the spinal stability during pushing and pulling exertions. Past studies suggest that the spine can be stabilized by paraspinal muscle stiffness as well as reflexes. We hypothesized that the stability of the spine decreases with exertion force and decreases during pushing more than during pulling exertion. Kinematic variability and nonlinear dynamic stability measurements were quantified from the balance performance during isometric pushing and pulling tasks. Results demonstrated that spinal stability decreased with exertion force and decreased a greater amount during pushing task than during pulling task. Stiffness alone may be insufficient to stabilize the trunk. Results may be able to be explained by slower reflex delay. The results suggested that pushing and pulling exertions have a potential risk of low-back disorders. / Master of Science

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