This study explores the combined effects of backpack loading and smartphone dual tasking on gait dynamic stability. Unlike previous separate investigations, it systematically examines their individual and interactive influences on postural stability. An experimental protocol simulated smartphone use during backpack-loaded walking. Kinematic and kinetic data from 15 female university students were collected via 3D motion capture and analyzed using inverse dynamics. An innovative computational method assessed margin of stability (MOS), investigating biomechanical mechanisms of postural instability. Smartphone tasks disrupt pelvic, lumbar, and lower limb kinetics/kinematics, reducing walking speed and increasing instability risk. Backpack loading altered knee range of motion and ankle/metatarsophalangeal moments, with 15% body weight (BW) loads showing significant destabilizing effects. Instability correlated strongly with hip, lumbar, and metatarsophalangeal parameters. Combined tasks exacerbated effects, including reduced gait velocity and the kinematic parameters and degrees of freedom variations. Both backpack loading and mobile phone dual tasking significantly altered movement characteristics, force exertion patterns, and gait stability during walking in the pelvis, hip joints, and lumbar spine, with demonstrable interaction effects between these factors. Across the pelvis, hip joints, lumbar spine, and lower extremity joints, adaptations in joint range of motion and peak moments generated distinct mechanical adjustments to compensate for attentional distraction and center-of-mass deviation induced by these combined variables.
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