Affiliations: School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
Correspondence:
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Corresponding author: Scott Netson MacKinnon, School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland A1C 5S7, Canada. Tel.: +1 709 737 8807; Fax: +1 709 737 3979; E-mail: smackinn@mun.ca
Abstract: This study examined the effects that specific postures had on the neuromuscular activities of four muscles during an isoinertial pulling task. Ten male subjects volunteered to execute one-handed pulls at 15% of their body mass, at a frequency of 12 pulls per minute, for a duration of 12.5 minutes in both a standing and sitting posture. Electromyographical (EMG) activities of the posterior deltoid, trapezius, latissimus dorsi and erector spinae (L4/L5 level) were recorded by a portable data collection system using bipolar surface electrode configurations. Collected EMG data were subsequently analysed for differences in magnitude and rate of fatigue between conditions. Heart rates were also recorded for both conditions. Cardiovascular and neurophysiological responses provided no evidence of fatigue due to the execution of the task, suggesting that these workload and postures would be suitable for industrial applications. Analyses revealed significant differences between conditions in the level of activation for all muscles except the trapezius, suggesting that muscle recruitment is highly influenced by posture during common pulling activities. These findings support a conclusion that an operator performing repetitive submaximal (i.e. less than 15% of a subject's absolute body mass) pulling tasks would benefit from a workstation designed to accommodate standing and sitting postures in order to vary the manner in which agonist muscles are recruited.
