Changes in synergy formation and modulation during cyclic finger force production tasks in female adults with...

The present study investigated alterations in multi-element coordination in female adults with dystonic cerebral palsy (DCP), focusing on finger forces and forearm muscle activity. Despite their clinical significance, coordination impairments in this population remain to be fully elucidated. Participants diagnosed with DCP and healthy controls performed maximal and submaximal repetitive isometric force-production tasks involving finger flexion and extension. Electromyographic activity was recorded from forearm flexor and extensor muscles. The analysis of finger-force and muscle-activation patterns was conducted within the uncontrolled manifold framework to quantify multi-element coordination, i.e., synergy index. It was hypothesized that the DCP group would demonstrate diminished force- and muscle-level synergy indices, augmented muscle co-contraction, and diminished performance consistency in comparison to the control group. In comparison with the control group, participants with DCP exhibited lower maximal forces, greater unintended force production by non-task fingers, and reduced consistency in peak and trough force production. During repetitive force production, the DCP group also demonstrated lower force-level synergy indices and weaker phase-dependent modulation, suggesting impaired stabilization of total finger force. These deficits were accompanied by increased flexor-extensor co-contraction and a condition-specific reduction in muscle-level synergy. In summary, female adults diagnosed with DCP demonstrated impaired multi-finger coordination at both the behavioral and neuromuscular levels. These findings suggest altered coordinative strategies that potentially involve subcortical mechanisms; however, the present results do not establish a direct neural mechanism. Future studies that integrate neurophysiological and functional assessments may elucidate the mechanisms underlying these impairments and their relevance to daily functioning.