This study investigated the effect of precision on time to task failure in a repetitive whole-body manual handling task. Twelve participants were required to repetitively lift a box weighing 65% of their single repetition maximum to shoulder height using either precise or unconstrained
box placement. Muscle activity, forces exerted at the ground, 2D body kinematics, box acceleration and psychophysical measures of performance were recorded until task failure was reached. With precision, time to task failure for repetitive lifting was reduced by 72%, whereas the duration taken
to complete a single lift and anterior deltoid muscle activation increased by 39% and 25%, respectively. Yet, no significant difference was observed in ratings of perceived exertion or heart rate at task failure. In conclusion, our results suggest that when accuracy is a characteristic of
a repetitive manual handling task, physical work capacity will decline markedly.
Practitioner Summary: The capacity to lift repetitively to shoulder height was reduced by 72% when increased accuracy was required to place a box upon a shelf. Lifting strategy and muscle activity were also
modified, confirming practitioners should take into consideration movement precision when evaluating the demands of repetitive manual handling tasks.
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maximal lift capacity;
Document Type: Research Article
Centre for Human and Applied Physiology, Faculty of Science, Medicine and Health, University of Wollongong, Wollongong, Australia
School of Health and Society, Faculty of Social Sciences, University of Wollongong, Wollongong, Australia
September 2, 2014
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