Passive Lower Back Moment Support in a Wearable Lifting Aid: Counterweight Versus Springs

Passive wearable lifting aids support workers by applying gravity force compensation at the arms. In this study we investigated the feasibility of a compensatory lower back moment, generated by a practically constant spring force (38.5 Nm), extending the lower back by pushing on the upper leg. This design is proposed as a light-weight solution to generate lower back moments. The method is compared to using counterweights at a different distances. We recorded EMG activity of the erector spinae longissimus (ES) muscle, the perceived workload (NASA TLX) and the preference of 12 subjects. Results showed no significant difference in ES peak EMG activity during the task, and no significant difference between perceived workload between conditions, as we expected. However, 10 out of 12 subjects indicated preferring the spring mechanism over both counterweights. The main reason of preference was the reduction of weight and inertia of the system. Therefore, the proposed constant spring force mechanism is a feasible alternative to counterweights.