Force frequency structure below 1 Hz in chronic stroke: Paretic arm control

• Coupled bilateral movement training reduced force variability in the paretic hand.
• Reduction in force variability was associated with decreased power in 0−0.41 Hz.
• Reorganized force frequency structure below 1 Hz indicates stroke motor recovery.

This study investigated force variability and frequency structure below 1 Hz to determine whether coupled bilateral training and neuromuscular stimulation facilitated force control in paretic arms. Fifteen chronic stroke participants received 9 h of coupled bilateral movement training. Unilateral and bilateral force control tasks were administered before and after rehabilitation. Repeated measures ANOVAs were performed on the: (a) coefficient of variation and (b) absolute and relative power below 1 Hz in the paretic hand. Further, a multiple linear regression analysis determined the relationship between the coefficient of variation and frequency power. Three significant rehabilitation findings indicated: (a) reduced force variability across unilateral and bilateral force control conditions, (b) decreased absolute power in 0.09−0.41 Hz and 0.59−1.08 Hz whereas increased relative power in 0.59−1.08 Hz during unilateral force control, and (c) reduced absolute and relative power in 0.09−0.41 Hz that were associated with decreased variability during both unilateral and bilateral force control. Improved force variability in controlling unilateral paretic arms after training was attributed to less power below 0.41 Hz. Reorganization of the force frequency structure appears as a prominent component in force control improvements in paretic arms.