title: Precision markedly attenuates repetitive lift capacity.
abstract: 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.
  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.
authors.affiliation: a Centre for Human and Applied Physiology, Faculty of Science, Medicine and Health , University of Wollongong , Wollongong , Australia.
authors.forename: Brooke R
authors.initials: BR
authors.lastname: Collier
authors.forename: Laura
authors.initials: L
authors.lastname: Holland
authors.forename: Deirdre
authors.initials: D
authors.lastname: McGhee
authors.forename: John A
authors.initials: JA
authors.lastname: Sampson
authors.forename: Alison
authors.initials: A
authors.lastname: Bell
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Stapley
authors.forename: Herbert
authors.initials: H
authors.lastname: Groeller
mesh_terms: D061725:Accelerometry; D000293:Adolescent; D001696:Biomechanical Phenomena; D057645:Deltoid Muscle / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006339:Heart Rate; D006801:Humans; D017770:Lifting; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D011601:Psychophysics; D013647:Task Performance and Analysis; D014938:Work Capacity Evaluation; D055815:Young Adult
keywords: fatigue; maximal lift capacity; occupation; performance; precision; strength