Biomechanical assessment of manual handling to enhance workplace safety based on gait and center of mass analysis

Abstract

Manual material handling (MMH) in informal sectors is a significant contributor to work-related musculoskeletal disorders (MSDs), often resulting from unstable load carriage and poor ergonomic practices. This study investigates the biomechanical impact of traditional load-carrying techniques - on the shoulder (CoS), on the back (CoB) - in comparison with a newly designed ergonomic backpack (CoBp), focusing on gait stability, center of mass (COM) dynamics, and lower limb kinematics. Fifteen healthy male participants (mean age: 23.4 ± 1.6 years) performed gait trials under seven load conditions, while spatiotemporal, kinematic, and electromyographic (EMG) data were collected using inertial sensors and wireless surface EMG. Results revealed that the CoBp configuration significantly reduced COM displacement in both horizontal and vertical directions, with a 33% decrease in lateral COM excursion compared to CoB_20 (from 55.2 mm to 37.1 mm) and a 20% reduction in COM height (from 0.91 m to 0.73 m). Additionally, cadence increased from 107.2 steps/min in CoS_20 to 113.1 steps/min in CoBp_20, approaching the normal walking cadence of 111.0 steps/min. Double support phase, a key indicator of stability, was minimized in CoBp_20 (12.4%) compared to CoB_20 (18.2%). Joint kinematics showed reduced range of motion (ROM) at the hip and knee under CoBp, while EMG data indicated a more balanced muscle activation pattern with less asymmetry between the left and right lower limbs. These findings highlight that the proposed backpack design enhances dynamic stability, improves load symmetry, and minimizes lower limb strain during loaded gait. The study establishes CoBp as a biomechanically superior alternative for MMH, with implications for ergonomic interventions across occupational settings.