Adaptability of gait in stroke survivors

Background: Stroke survivors fall more often, mostly due to stumbling and slipping; which may signify. These causes of falls are hypothesized to be caused by difficulty in controlling and adjusting foot placement in response to the environment. In healthy adults’ foot placement control is known to be influenced by balance control, available response time and executive function. All these factors are known to be affected by stroke; however, how these factors affect foot placement accuracy in stroke survivors is largely unknown. The overarching aim of this thesis is therefore to understand the role of these factors in the control of foot placement following stroke and by extension to better understand how foot-placement is controlled, the causes of stroke related impairments and potential reasons for falls. Methods/Results: Young (n=14) and older healthy adults (n=9) and stroke survivors (n=13) completed a series of experiments on a C-Mill (a force instrumented treadmill with visual projection of stepping targets) designed to assess the role of balance (study 1), response time (study 2) and executive function (study 3) on foot placement control in stroke survivors. Study 1 compared foot placement control in supported versus unsupported conditions; balance support reduced overall error while target stepping (main effect F (1,30)=18.141, p<0.001), but mostly in stroke survivors. Study 2 compared foot placement control when targets could be seen in advance (planned) with targets appearing at midstance (reactive). Foot-placement error altered according to direction of step but not available response time, with significant increase in error (F (1,28) =6.013, p=0.021) when adjusting steps medio-laterally but decreased when adjusting steps anterio-posterially (F (1,28) = 5.932, p=0.021). Overall, stroke survivors missed about 10% of targets and undershot all targets while young healthy adults undershoot only lengthening steps. Study 3 evaluated the use of functional near-infrared spectrometry (fNIRS) to measure activation of prefrontal cortex activation (brain networks responsible for executive function) in target stepping conditions which can be expected to increase challenge to executive function. fNIRS showed high inter person variability and no systematic trends according to walking conditions. Conclusion: Stroke survivors miss about 1 in every 10 targets; in the real world this may lead to a fall. Balance support may generally help stroke survivors control foot-placement more accurately. However, the lack of difference in accuracy between reactive and pre-planned stepping indicates stroke survivors may respond to all foot-placement adaptations reactively (a “cluttered terrain strategy”). This ‘cluttered terrain strategy’ is indicative of increased cognitive control, however the use of fNIRS needs development to robustly be assess this during walking