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.

INTRODUCTION Central nervous system uses two main strategies to retain balance if it is distorted by a perturbation: (1) feed forward control or anticipatory postural adjustments (APA) prior to the expected body perturbations and (2) feedback control or compensatory postural adjustments (CPA) that are initiated by the sensory feedback signals after the perturbations. Our posture is controlled by the integration of information from the vestibular, proprioceptive, and visual systems. The purpose of this study was to investigate the role of altered proprioception on anticipatory (APAs) and compensatory (CPAs) postural adjustments. METHODS Nine healthy adults received external perturbations at the shoulder level while standing with intact or altered proprioception on an AMTI force platform. Experimental conditions were: normal and altered proprioception while eyes are open or closed. Proprioception was altered bilaterally by applying miniature vibrators over the Achilles tendon. Electrical activity of the trunk and leg muscles and center of pressure (COP) displacements were recorded. RESULTS When vision was available in eyes open condition with altered proprioception, APA was delayed (p<0.05). Moreover, altered proprioceptive information resulted in smaller magnitude of CPA. Smaller COP displacements were recorded after the perturbation in both eyes open and eyes closed conditions. DISCUSSION Alteration of proprioception of the lower extremity in the presence of vision induces significant delays of APA. Moreover, the subjects’ demonstrated that irrespective of the availability of vision, altered proprioception was associated with a reduction of CPA and lesser COP displacements after perturbation.

Side effects associated with cancer treatments can lead to postural instability. Balance and posture in cancer survivors has received limited attention. Traditional center of pressure (COP) measures have previously been shown to be sensitive to changes in vision and surface conditions in cancer survivors. Time-to-boundary (TTB) predicts the time it would take the COP to reach the limits of the base of support. It’s unclear whether TTB provides information beyond the traditional COP measures of posture and balance in cancer survivors. The purpose of this study was to determine whether TTB could be predicted by traditional COP measures, which were previously found to be sensitive to changes in vision and surface conditions. METHODS Quiet standing was measured in participants on a rigid surface with eyes open and eyes closed, compliant surface with eyes open and eyes closed. Force data were collected for 30s at 1000Hz. COP data were resampled at 50Hz for TTB assessments. The TTB algorithm was based on previous literature. Stepwise linear regression was used to determine whether TTB could be predicted based on traditional COP measures which previously showed sensitivity to conditions. Ten measures were used as predictive variables. RESULTS Four significant regression models were identified. No model explained more that 58% of the variance in TTB, suggesting traditional COP measures aren’t good predictors, and TTB may provide further insight into mechanisms underlying posture and balance

Sitting is the most functional posture for play and exploration in developing children; usually attained by 6-7 months of age. However, children with cerebral palsy (CP) have significant deficits in sitting attainment, and hence are restricted in interaction. We compared two interventions to promote sitting postural control in children with severe CP, for effects on behavioral and kinetic measures. Gross Motor Function Measure (GMFM), was used to code behavioral changes pre/post intervention; when COP data were also collected. Ten children with moderate or severe CP were randomized into 2 intervention groups. One group received a perceptual motor intervention, the other group received the same intervention plus stochastic noise at the support surface. Repeated measures 2X2 ANOVA (treatment X time)assessed GMFM and COP; p<0.1. There was a significant effect of time for GMFM, but no difference between groups. There was a significant interaction effect for RMS (variability of COP path) in the anterior posterior (AP) direction (p=0.1), and Approximate Entropy in the AP (p=0.08). In both cases, the group with stochastic noise intervention developed in the same direction as expected for typically developing infants in sitting. We conclude that while both interventions produced behavioral changes in sitting skill, the group with stochastic noise added during intervention showed specific improvement in variability and complexity of the COP, which mirrored developmental changes in typical infants’ sitting postural control. Results indicate potential for greater change using the stochastic noise intervention, and thus greater function as sitting skill progresses.