Multi-joint Synergistic Isokinetic Training via a Variable-impedance Tunnel Constraint for Upper-limb Rehabilitation

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Abstract

Conventional isokinetic dynamometers control angular velocity about a single joint axis, whereas functional upper-limb movements involve multiple joints. To address this limitation, this paper proposes multi-joint synergistic isokinetic training, an active-resistance approach implemented on a 3-DOF upper-limb exoskeleton with a variable-impedance tunnel constraint (VITC). A prescribed task-space velocity ceiling establishes isokinetic resistance, while the VITC permits voluntary spatial variation within a free-motion core and progressively activates corrective and safety constraints as deviation increases. The reconstructed end-effector speed approached the three nominal settings, with small peak overshoots at 0.10 and 0.15 m/s. In the perturbation trial, the maximum radial deviation was 104 mm, 4 mm beyond the nominal tunnel boundary. In a five-subject comparison with isotonic free-weight exercise, the proposed training produced higher muscle activation, with significant increases in the biceps and triceps brachii (t-test). These results demonstrate multi-joint synergistic isokinetic training as a new patient-active and multi-joint rehabilitation paradigm.

Keywords

Upper-limb exoskeleton / Isokinetic training / Variable-impedance control / Task-oriented rehabilitation

CHANGE HISTORY

A Correction to this paper has been published:
https://doi.org

The Retraction Note was updated to reflect reception of statements of disagreement from all authors.

This article has been retracted.Please see the Retraction Notice for more detail:
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The Author(s) 2026. This article is published by Higher Education Press

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