In our earlier experiment, we observed intact force-control capabilities in individuals post-stroke during locomotion without postural influence. We sought to better understand the mechanisms underlying the interaction of locomotor and postural control and the role of postural control as an interactive mechanism that might interfere with appropriate foot-force generation. We designed an experiment in which subjects performed biomechanically-controlled locomotion, under posturally challenged pedaling while generating force outputs comparable to pedaling without postural challenge, thus allowing us to monitor the different strategies by the nervous system when postural conditions were manipulated. We hypothesized that with postural influence, individuals post-stroke will generate inappropriate shear forces accompanied by inappropriate coupling of muscle activity, and will be exaggerated with increased postural loading. Methods: Post-stroke (n=11) and non-impaired (n=5) individuals pedaled on a cycle ergometer under (1)seated, and (2)non-seated postural-loaded conditions, generating matched pedal normal force, with the motor-driven crank moving at 40rpm. Forces and EMG were recorded and analyzed offline. Results: During seated pedaling, we observed comparable shear pedal forces in both groups. During non-seated postural-loaded pedaling, we observed greater forward-directed shear forces in individuals post-stroke, but not in controls, which were exaggerated with increased postural loading. With postural influence, individuals post-stroke showed increased SOL and RF activities, whereas, in non-impaired controls we observed decreased VM, RF and BF activity. Conclusion: Reduced force-control capabilities during locomotion only when postural mechanisms were involved, suggests impaired interaction between locomotion and posture in the post-stroke nervous system. This inability to regulate postural loads may compromise the ability to adapt and react to changes in environmental conditions during walking, and could result in slips and falls.
Listed In: Neuroscience, Other