# The efficacy of different torque profiles for weight compensation of the hand

## TL;DR

This study compares different wrist support strategies to help people with muscle weakness maintain a neutral hand position and reduce strain.

## Contribution

The study shows simplified torque profiles are as effective as the ideal sinusoidal profile for wrist weight compensation.

## Key findings

- All compensation strategies reduced anti-gravity muscle activity by 47–53%.
- All strategies increased flexor muscle activity by 44–61% in higher palmar flexion.
- No significant differences were found between the compensation strategies.

## Abstract

Orthotic wrist supports will be beneficial for people with muscular weakness to keep their hand in a neutral rest position and prevent potential wrist contractures. Compensating the weight of the hands is complex since the level of support depends on both wrist and forearm orientations. To explore simplified approaches, two different weight compensation strategies (constant and linear) were compared to the theoretical ideal sinusoidal profile and no compensation in eight healthy subjects using a mechanical wrist support system. All three compensation strategies showed a significant reduction of 47–53% surface electromyography activity in the anti-gravity m. extensor carpi radialis. However, for the higher palmar flexion region, a significant increase of 44–61% in the m. flexor carpi radialis was found for all compensation strategies. No significant differences were observed between the various compensation strategies. Two conclusions can be drawn: (1) a simplified torque profile (e.g., constant or linear) for weight compensation can be considered as equally effective as the theoretically ideal sinusoidal profile and (2) even the theoretically ideal profile provides no perfect support as other factors than weight, such as passive joint impedance, most likely influence the required compensation torque for the wrist joint.