Affiliations: [a] School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland, Canada | [b] Department of Human Biology, University of Cape Town, Cape Town, South Africa
Correspondence:
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Address for correspondence: Scott N. MacKinnon, Ph.D., School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1C 5S7. Tel.: +1 709 737 8807; Fax: +1 709 737 3979; E-mail: smackinn@mun.ca
Abstract: This study examined the effects of reach distance on the lumbar spine kinematics and electromyographical activities (EMG) of eight selected muscles of the trunk and shoulder during submaximal horizontal pulling exertions (12% of lean body mass) all located at elbow height. Eleven healthy male volunteer subjects were asked to pull on a load located at varying distances (10, 15, 20, 25, 30, 35 and 40% of subject stature) from the frontal plane containing the load handle. Trunk kinematics in the sagittal plane, as monitored by a Lumbar Motion Monitor, increased significantly as reach distance increased. EMG data revealed increasing erector spinae activity as reach distance increased and this muscle group was found to be co-active with external oblique muscles during the exertion. Shoulder complex muscles were found to be highly active in all conditions, but only the trapezius and deltoid demonstrated significantly decreasing activity as pull reach increased. These data provide some direction in positioning the operator within a workstation demanding pull force exertions.
