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Michael W. Holmes, Scott N. MacKinnon, Julie Matthews, Wayne J. Albert, and Steven Mills

Seafaring occupations have been shown to place operators at an increased risk for injury. The purpose of this study was to understand better the demands of a moving environment on the ability of a person to perform specific lifting tasks. Subjects lifted a 15-kg load under four different lifting conditions. A 6-degree-of-freedom ship motion simulator imposed repeatable deck motions under foot while subjects executed the lifting tasks. Subjects were oriented in three different positions on the simulator floor to inflict different motion profiles. Electromyographic records of four muscles were collected bilaterally, and thoracolumbar kinematics were measured. A repeated-measures ANOVA was employed to assess trunk motions and muscle activities across lifting and motion conditions. The erector spinae muscles showed a trend toward significant differences for motion effects. Maximal sagittal velocities were significantly smaller for all motion states in comparison with the stable condition (p ≤ .01), whereas maximum twisting and lateral bending velocities were higher (p ≤ .05). Results suggest working in a moving environment will likely increase the operator’s risk for overexertion injuries, particularly to the trunk region.

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Rebecca J. Giorcelli, Richard E. Hughes, Richard S. Current, and John R. Myers

This paper describes a procedure developed and validated to assess the accuracy of an infrared-based motion measurement system used to perform a kinematic analysis of the torso with respect to the pelvis during simulated lifting tasks. Two rigid reflective marker triads were designed and fabricated for attachment to the thorax over the 6th thoracic vertebra and the pelvis. System accuracy was assessed for planar rotation as well as rotations about multiple orthogonal axes. A test fixture was used to validate known triad orientations. The spatial coordinates of these triads were collected at 120 Hz using a ProReflex motion measurement system. Single value decomposition was used to estimate a rotation matrix describing the rigid body motion of the thorax triad relative to the sacral triad at each point in time. Euler angles corresponding to flexion, lateral bending, and twisting were computed from the rotation matrix. All measurement error residuals for flexion, lateral bending, and twisting were below 1.75°. The estimated mean measurement errors were less than 1° in all three planes. These results suggest that the motion measurement system is reliable and accurate to within approximately 1.5° for the angles examined.

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Carolyn A. Duncan, Scott N. MacKinnon, and Wayne J. Albert

The purpose of this study was to examine how wave-induced platform motion effects postural stability when handling loads. Twelve participants (9 male, 3 female) performed a sagittal lifting/lowering task with a 10 kg load in different sea conditions off the coast of Halifax, Nova Scotia, Canada. Trunk kinematics and foot center of force were measured using the Lumbar Motion Monitor and F-Scan foot pressure system respectively. During motion conditions, significant decreases in trunk velocities were accompanied by significant increases in individual foot center of pressure velocities. These results suggest that during lifting and lowering loads in moving environments, the reaction to the wave-induced postural disturbance is accompanied by a decrease in performance speed so that the task can be performed more cautiously to optimize stability.

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Yu Shu, Jonathan Drum, Stephanie Southard, Gwanseob Shin, and Gary A. Mirka

There are many outdoor work environments that involve the combination of repetitive, fatiguing lifting tasks and less-than-optimal footing (muddy/slippery ground surfaces). The focus of the current research was to evaluate the effects of lifting-induced fatigue of the low back extensors on lifting kinematics and ground reaction forces. Ten participants performed a repetitive lifting task over a period of 8 minutes. As they performed this task, the ground reaction forces and whole body kinematics were captured using a force platform and magnetic motion tracking system, respectively. Fatigue was verified in this experiment by documenting a decrease in the median frequency of the bilateral erector spinae muscles (pretest-posttest). Results indicate significant (p < 0.05) increases in the magnitude of the peak anterior/posterior (increased by an average of 18.3%) and peak lateral shear forces (increased by an average of 24.3%) with increasing time into the lifting bout. These results have implications for work environments such as agriculture and construction, where poor footing conditions and requirements for considerable manual materials handling may interact to create an occupational scenario with an exceptionally high risk of a slip and fall.

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-Dimensional Torso Kinematics during Manual Materials Handling Rebecca J. Giorcelli 1 Richard E. Hughes 2 Richard S. Current 3 John R. Myers 3 5 2004 20 2 185 194 10.1123/jab.20.2.185 Subject-Specific Estimates of Tendon Slack Length: A Numerical Method Kurt Manal 1 Thomas S. Buchanan 1 5 2004 20 2 195

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Original Research Manual Materials Handling in Simulated Motion Environments Michael W. Holmes * Scott N. MacKinnon * Julie Matthews * Wayne J. Albert * Steven Mills * 5 2008 24 2 103 111 10.1123/jab.24.2.103 Research Power-Time, Force-Time, and Velocity-Time Curve Analysis during the

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Jonathan S. Dufour, Alexander M. Aurand, Eric B. Weston, Christopher N. Haritos, Reid A. Souchereau, and William S. Marras

the acceptable position threshold of 5° presented by Robert-Lachaine et al 35 for manual materials handling tasks. Errors were comparable in the low back and neck but were highest in the right shoulder. Task difficulty did not affect error or accuracy measures except for increased errors and reduced