Using a Passive Back Exoskeleton During a Simulated Sorting Task: Influence on Muscle Activity, Posture, and Heart Rate

Objective To evaluate using a back exoskeleton in a simulated sorting task in a static forward bent trunk posture on muscle activity, posture, and heart rate (HR). Background Potentials of exoskeletons for reducing musculoskeletal demands in work tasks need to be clarified. Methods Thirty-six healthy males performed the sorting task in 40 degrees-forward bent static trunk posture for 90 seconds, in three trunk orientations, with and without exoskeleton. Muscle activity of the erector spinae (ES), biceps femoris (BF), trapezius descendens (TD), rectus abdominis (RA), vastus laterals (VL), and gastrocnemius medialis was recorded using surface electromyography normalized to a submaximal or maximal reference electrical activity (%RVE (reference voluntary electrical activity)/%MVE). Spine and lower limb postures were assessed by gravimetric position sensors, and HR by electrocardiography. Results Using the exoskeleton resulted in decreased BF muscle activity [-8.12%RVE], and minor changes in ES [-1.29%MVE], RA [-0.28%RVE], VL [-0.49%RVE], and TD [+1.13%RVE] muscle activity. Hip and knee flexion increased [+8.1 degrees; +6.7 degrees]. Heart rate decreased by 2.1 bpm. Trunk orientation had an influence on BF muscle activity. Conclusion Using the back exoskeleton in a short sorting task with static trunk posture mainly reduced hip extensor muscle activity and changed lower limb but not spine posture. Implications of using a back exoskeleton for workers' musculoskeletal health need further clarification. Application The detected changes by using the Laevo (R) illustrate the need for further investigation prior to practical recommendations of using exoskeletons in the field. Investigating various work scenarios in different kind of workers and long-term applications would be important elements.