Passive Exoskeletons Reduce Low-Back Passive Tissue Creep

ObjectiveThe objective of the current study is to investigate how passive exoskeletons affect low-back passive tissues creep during prolonged stooping.BackgroundUsing exoskeletons could be a new strategy to prevent stress-relaxation deformation (creep) in low-back passive tissues induced by prolonged or repetitive stooping, but previous studies only focused on low-back active tissues.MethodTwelve healthy males completed 12 min of stooping (with and without a passive exoskeleton), while body kinematics and muscle activities were captured before and after stooping.ResultsResults indicate intact characteristics (i.e., no changes) in both active and passive tissues after enduring a 12-min stooping protocol while using the exoskeleton. However, without the exoskeleton, clear stress-relaxation deformation in low-back tissues, and changes in the load transfer mechanism between active and passive tissues after prolonged stooping, are observed, revealing a 3.19° delayed flexion-relaxation angle, a 5% maximum voluntary contraction increase in lumbar muscle activity, and a 2.8° increase in the maximum lumbar flexion angle.ConclusionThe supporting force provided by passive exoskeletons effectively limits stress-relaxation deformation in low-back passive tissues, such as ligaments, by preventing excessive elongation during prolonged stooping in a fully flexed posture, thereby reducing the possible risk of spinal instability and low back pain development.ApplicationThe study reveals the greater value of passive exoskeletons, which protect passive tissues in the low back. The research findings can serve as a valuable reference for practitioners in implementing effective countermeasures in the perspective of assistance devices to enhance occupational safety.