Ergonomic Benefits of an Angle Grinder With Rotatable Main Handle in a Cutting Task

Objective: The aim of this study was to evaluate the ergonomic benefits of an angle grinder with a rotatable main handle in a cutting task. Background: Angle grinder manufacturers rarely address ergonomic features in their advertisements, and if they do, the benefits are expressed in a qualitative manner. Meanwhile, quantitative information about the effects of the device on the worker is required to make informed decisions during tool selection and cumulative trauma prevention. Method: Eleven maintenance workers and metalworkers used an angle grinder to cut a horizontal steel rod using three wrist postures. Only one of the postures was exclusively available in the case of a rotatable main handle. The postural effect was evaluated objectively with electromyography and a force-sensing-resistor-based force glove. Subjective ratings about discomfort and control were obtained with a visual analog scale. Results: The subjective ratings favor the near-neutral wrist posture. The forearm muscles’ electromyographic activities were similar across the postures. Forces on the hand–handle interface were concentrated on the intermediate phalanges. If the device is operated without gloves, the forces on the intermediate phalanges may exceed the discomfort pressure threshold regardless of wrist posture. Conclusion: In the cutting task, the subjective measures favor the posture with a near-neutral wrist, which is a feature of the rotatable main handle. The objective measures did not allow one to prefer one posture to another. Application: The findings give insight into the impact of wrist posture on muscle activity, forces on the hand–handle interface, and discomfort. This is useful information for the person responsible for tool selection.