A Biomechanical Analysis of a Specialized Load Carriage Technique and the Development of an Assistive Load Carriage Device

Abstract

During field observations of professional movers, it was noticed that some experienced movers carried loads posterior to their pelvis. The purpose of this study was two-fold: (1) to assess the biomechanical differences between hand-held load carriage anterior (AC) and posterior (PC) to the pelvis; and, (2) to determine if an assistive load carriage device could reduce muscle effort while carrying loads either anterior or posterior to the pelvis. In the first laboratory study, an electromyographic (EMG) analysis was conducted while participants carried a load on a treadmill using AC and PC techniques. The subjects conducted three trials of AC and PC techniques while EMG data were being collected. All trial data were normalized to their respective iMVE values. An amplitude probability distribution function (APDF) was used to compare EMG amplitudes between carrying techniques. Results indicated that PC reduced EMG activity of the erector spinae (>50% reduction), trapezius, and anterior deltoid (p<0.05) as well as increasing EMG activity in the posterior deltoid (p<0.05). Eighty percent of the subjects reported that the PC method felt awkward. Due to its awkwardness, many individuals may not use the PC technique; thus, the second purpose of the study was to design an assistive movers’ pack to aid in AC and PC techniques and make the PC method easier to perform. In the second study, subjects were asked to walk unloaded while EMG was recorded. The subjects then performed the AC and PC methods with and without the assistive device. All EMG signals were normalized to unloaded gait followed by EMG APDF analyses. Findings from the first study were confirmed, in that PC, compared to AC significantly reduced erector spinae activity (p<0.05) and focused shoulder activity to the posterior deltoid. Secondly, the assistive device effectively reduced flexor digitorum activity (>40% reduction, p<0.03) and anterior deltoid activity (>75% reduction, p=0.5) in both AC and PC. Erector spinae EMG remained similar to their respective unassisted conditions. The assistive load carriage device may be an effective ergonomic tool in both AC and PC techniques. Subjective surveys indicate that the assistive device decreased the awkwardness in performing the PC technique.