Roles of load-induced reorganization of multi-digit physiological tremors for a tracking maneuver.

This study was undertaken to investigate the effect of low-level loading on digit tracking and the associated physiological tremors in the moving and the stationary digits. Sixteen healthy adults conducted positional tracking with the middle finger under the loaded and unloaded conditions; meanwhile, trajectory of the middle finger, electromyographic activities of the extensor digitorum (ED)/flexor digitorum superficialis, and physiological tremors of the index, middle, ring, and little fingers were recorded. The results showed that load imposition (<70 g) on the middle finger improved tracking congruency, in association with reduction of inter-digit tremor coupling and enhancement of tiny movement jerks. Principal component analysis suggested that inertial load suppressed the 8-12 Hz central rhythm but potentiated the 25-40 Hz coherence spectra of major principal components and electromyographic signals of the ED. It was concluded that low-level inertial load could facilitate corrective movement adjustments and selective digit control during manual tracking, relevant implicitly to decreased common central drive and enhanced heteronymous reflex loops.