Impaired foot-force direction regulation during postural loaded locomotion in individuals poststroke

Abstract

Following stroke, hemiparesis results in impaired motor control. Specifically, inappropriate direction of foot-forces during locomotion has been reported. In our previous study (Liang and Brown 2011) that examined poststroke foot-force direction during a seated, supported locomotor task, we observed that foot-force control capabilities were preserved poststroke. In this current study, we sought to better understand the mechanisms underlying the interaction of locomotor and postural control as an interactive mechanism that might interfere, poststroke, with appropriate foot-force generation. We designed an experiment in which participants performed biomechanically controlled locomotor tasks, under posturally challenged pedaling conditions while they generated mechanical output that was comparable to pedaling conditions without postural challenge, thus allowing us to monitor the strategies that the nervous system adopts when postural conditions were manipulated. We hypothesized that, with postural influence, individuals poststroke would generate inappropriate shear forces accompanied by inappropriate changes to muscle activity patterns when performing a mechanically controlled locomotor task, and would be exaggerated with increased postural loading. Sixteen individuals with chronic poststroke hemiparesis and 14 age-similar nonimpaired controls pedaled on a cycle ergometer under 1) seated supported and 2) nonseated postural loaded pedaling conditions, generating matched pedal force outputs of two effort levels. When we compared postural influence with seated pedaling, we observed increased magnitudes of forward-directed shear forces in the paretic legs associated with increased magnitude of leg extensor muscle activity, but not in controls. These findings provide evidence to support a model that describes independent controllers for posture and locomotion, but that the interaction between the two controllers is impaired poststroke.

Does visual feedback during walking result in similar improvements in trunk control for young and older healthy adults?

“…The lack of difference on the measured gait parameters between feedback conditions demonstrates that average spatial/temporal aspects of walking were unchanged, despite reduced AP and ML trunk translation in space. This is consistent with the idea that cyclic behavior of the legs, path consistency and upright orientation are separate tasks during walking [7,27,50], and demonstrates that path consistency can be modified independent of changes to the average walking pattern. The implication for rehabilitation is that isolated functional impairments in COM translation control may be effectively improved during walking using concurrent visual FB.…”

Foot force direction control during a pedaling task in individuals post-stroke

“…Evidence suggested that addition of postural control could interfere with locomotor output in people post-stroke during a standing, non-seated pedaling task [16]. Thus, further research must be conducted to determine whether inappropriate shear forces will be revealed under non-seated, postural demanding conditions, where subjects have to actively control for posture [17]. …”

Limb contribution to increased self-selected walking speeds during body weight support in individuals poststroke

“…Massion suggests that the neural control of posture and locomotion are separate, but interacting controllers for normal walking [8]. Previously, Liang and Brown suggested that Massion’s model may be altered poststroke, such that the requirement for generating vertical support forces during locomotion interferes with regulation of foot force direction [9]. The current study suggests reducing the vertical support requirement of locomotion with BWS may result in less interference of postural control centers on locomotor control.…”