Steering the Path with a Semi-Passive Robot to Break Post-Stroke Synergies

Abnormal coupling of elbow flexors with shoulder abductors-the "flexor synergy"-is a common post stroke motor impairment that interferes with upper extremity function. Previous studies have shown that practicing elbow extension while loading shoulder abductors can improve independent joint control. However, these approaches often involve expensive and bulky equipment, limiting their use in clinic. SepaRRo is a semi-passive rehabilitation robot that uses brakes to generate training forces, reducing its cost relative to existing systems. SepaRRo can also load the shoulder abductors during horizontal planar reaching, suggesting that it could target the flexor synergy. However, it is unclear if training with a semi-passive robot can produce out-of-flexor synergy kinematic adaptations.

Chronic stroke survivors (n = 15) with upper extremity impairment participated in a randomized, crossover-design experiment where they reached for a functional target with their more-impaired limb in two conditions: SepaRRo resisting their motion to the target (Resistance), and SepaRRo generating an additional lateromedial force to load their shoulder abductors (Steering). For each condition, we measured changes in reaching kinematics with motion capture equipment.

Following the Steering condition, participants demonstrated significantly greater shoulder abduction than the Pre-test and the Resistance condition (p0.112). Participants reduced their el bow extension following the Resistance condition (p = 0.018).

Steering facilitated out-of-synergy adaptations that were not present following simple resistance.

Conventional training methods may facilitate post-stroke synergies and impede recovery, while SepaRRo's steering forces may lead to improvements in independent joint control in stroke survivors.