Exploratory Study of the Influence of Posture and Hand Task on Corticomotor Excitability of Upper Extremity Muscles After Stroke

Abstract Objective To explore the interaction between postural stability and hand task on the corticospinal excitability (CE) of upper extremity muscles and how it is affected by lesion location. Design Cross-sectional explorative survey. Setting Inpatient rehabilitation center. Participants Participants (N=81) were neurologically healthy subjects (volunteer sample, n=36) and patients with stroke (convenience sample, n=45; mean time since stroke, 45d), stratified according to lesion location: pure subcortical strokes (n=25) and strokes with cortical involvement (n=20). Interventions Not applicable. Main Outcome Measures Motor-evoked potentials were recorded simultaneously from the first dorsal interosseus (FDI) muscle and biceps brachii (BB) during rest and during low and forceful activation of the FDI in 4 different postural positions (supine, sitting, sitting unsupported, standing) and compared. Results Posture modulated CE of the FDI and BB during performance of a motor task but not at rest. The influence of postural position on CE of the FDI depended on force demand and lesion location: the control and subcortical stroke group demonstrated significantly higher CE of the FDI when performing the forceful task in the supine and stable sitting positions, respectively, compared with standing. In contrast, the cortical stroke group exhibited significantly higher CE of the FDI when performing the low-force task in a stable sitting position compared with standing. Conclusions Posture influences CE of the FDI and BB in healthy subjects and patients with stroke differentially depending on hand task, but not at rest. A stable sitting posture increased excitability of the FDI in patients with stroke. These findings imply that hand rehabilitation protocols may be influenced by posture.