Ergonomic assessment of a multi-joint actuated lower extremity exoskeleton to assist dynamic lifting and carrying tasks.

The proof-of-concept study for a hip and knee joint actuated exoskeleton developed for repetitive manual lifting and carrying tasks is investigated. Fifteen participants completed the study which involved two laboratory manual handling tasks of (1) lifting a box weighing 9.5 kg (repeated in three trials as a standalone task) and (2) lifting and carrying same box over a distance (repeated in three trials as a single combined task), with and without the use of the exoskeleton suit. Monopolar surface EMG sensors are utilized to capture participants muscular activity from two quadricep femoris muscles (i.e., the vastus medialis and rectus femoris) and a calf muscle (i.e., gastrocnemius) of the lower extremity. After each task repetition (trial), participants are asked to rate their perceived musculoskeletal effort on a scale of 0 to 100 (or 100%) where '100' represents the highest possible participant effort. We determine the 'onset' of fatigue for each participant based on the trial at which fatigue was first experienced. The exoskeleton is found to reduce average muscular activity of the vastus medialis (30-60%), rectus femoris (30-38%), and gastrocnemius muscles (40-58%). Participants' average rating of their lower-limb musculoskeletal effort when assisted by exoskeleton is found to be significantly less (26.9%) than their rating without the exoskeleton. However, subjective rating of fatigue differs significantly among the participants. These findings adds performance evaluation data for powered lower-extremity exoskeleton for strength augmentation in lifting and carrying works. Future studies should provide further insight into its potential use for prevention of cumulative trauma disorders of the lower-extremity.