Affiliations: [a] Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, ON, Canada | [b] Graduate Research and Education Programs, Canadian Memorial Chiropractic College, Toronto, ON, Canada | [c] Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, ON, Canada
Correspondence:
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Corresponding author: Jack P. Callaghan, Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada. Tel.: +1 519 888 4567, ext. 37080; Fax: +1 519 746 6776; E-mail: callagha@uwaterloo.ca
Abstract: In most genuine industrial settings, it is not yet feasible to directly measure in vivo tissue loads, nor is it practical to estimate dynamic load-time histories using biomechanical models. Thus, data extrapolation techniques are often used for obtaining occupational estimates of shift or daily cumulative low-back load exposures. These techniques are reliant on the assumption that the observed duty cycle of apparently stereotypical work is consistent over long working durations. This investigation evaluated the validity of this assumption using a controlled laboratory-based repetitive lifting task. Nine men performed 30-minutes of sagittal plane repetitive lifting tasks. Upper body kinematics were captured during the tasks, and a two-dimensional dynamic biomechanical model was used to generate peak and cumulative estimates of low-back loads. Over the course of the 30-minute testing sessions, kinematic adaptations at the elbow were responsible for an 8% reduction in duty cycle duration while peak low-back load magnitudes remained consistent. Combining reductions in duty cycle duration with negligible changes in peak loading contributed to a small decrease (⩽ 10%) in cumulative low-back load over the final 20-minutes of lifting. However, when data extrapolation was incorporated to estimate a shift exposure it was found that these changes could overestimate occupational cumulative low-back loading exposures by 10–27% inferences made regarding the risk of low-back pain or injury reporting associated with exposure.
Keywords: Spine loading, repetitive lifting, dynamic biomechanical model, kinematic adaptations, time series
