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Should Hands Be Restricted When Measuring Able-Bodied Participants to Evaluate Machine Learning Controlled Prosthetic Hands?

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Restriction of the unaffected hand and wrist as used in the study. Left: participants wore a wrist brace while holding a tennis ball to restrict wrist movements. Right: The hand was subsequently taped in using skin tape while holding the tennis ball to restrict movement of the thumb and fingers. The band of electrodes is shown at the bottom of both pictures.

When evaluating methods for machine-learning controlled prosthetic hands, able-bodied participants are often recruited, for practical reasons, instead of participants with upper limb absence (ULA). However, able-bodied participants have been shown to often perform myoelectric control tasks better than participants with ULA. It has been suggested that this performance difference can be reduced by restricting the wrist and hand movements of able-bodied participants. However, the effect of such restrictions on the consistency and separability of the electromyogram’s (EMG) features remains unknown. The present work investigates whether the EMG separability and consistency between unaffected and affected arms differ and whether they change after restricting the unaffected limb in persons with ULA. Methods: Both arms of participants with unilateral ULA were compared in two conditions: with the unaffected hand and wrist restricted or not. Furthermore, it was tested if the effect of arm and restriction is influenced by arm posture (arm down, arm in front, or arm up). Results: Fourteen participants (two women, age = 53.4±4.05) with acquired transradial limb loss were recruited. We found that the unaffected limb generated more separated EMG than the affected limb. Furthermore, restricting the unaffected hand and wrist lowered the separability of the EMG when the arm was held down. Conclusion: Limb restriction is a viable method to make the EMG of able-bodied participants more similar to that of participants with ULA. Significance: Future research that evaluates methods for machine learning controlled hands in able-bodied participants should restrict the participants’ hand and wrist.

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