Firstly, the CoP GED agrees within 100ms to kinematic algorithms suggested for use with stroke survivors walking on a treadmill. However, when greater time resolution is required, in, for example, response time tasks, even a 100ms difference in GED may be important and care should be taken to use the most robust method for these applications. Detailed
comparison of the different algorithms suggests that CoP GED may actually be more accurate than kinematic methods for stroke survivors during target stepping tasks. For the means of this thesis, determining mid stance to calculate target stepping error and present reactive targets, CoP GED is accurate enough, within 100ms.
Secondly, the representation of target position in the registration of CueFors1 in C- Mill has a linear offset with the representation in Qualisys space at the time of registration in CueFors1. This linear offset can be corrected for, and will be corrected for in the work of this
Ph.D., with the linear equation derived at previously .
Lastly, our results indicate the most apropriate measure for foot placement accuracy (i.e. fulfillment of task requirments) is CoFerror, which is not equivalent to CoP position under the foot. However, CoF may not be the method by which people control their foot placment onto targets. Conversely, because foot placement is closely linked with centre of mass acceleration (and therefore maintenance of balance) CoP position on the foot may
reflect mechanisms of balance impairement in participant groups. However,within this thesis CoFerrorwill be used as the measure of foot placement accuracy.
4
Pilot study
4.1 Introduction
The understanding of foot placement control and adaptations during walking is important because altering foot placement is the most effective means of balance control when walking (Winter, 1995; Winter, Mackinnon, Ruder, & Wieman, 1993). Stroke survivors have
difficulty adjusting foot placement to step over obstacles as well as with narrowing steps, and performance worsens under time pressure (Nonnekes et al., 2010; Weerdesteyn, van
Swigchem, van Duijnhoven, & Geurts, 2007). However, evidence on how foot placement is controlled during walking post-stroke is incomplete. Current knowledge is largely derived from studies in standing investigating obstacle avoidance or target stepping during walking and predominantly focused on most directions except step narrowing during walking. A recent systematic review of gait adaptability (Balasubramanian et al., 2014) has called for the development of measures which capture all aspects of gait adaptability. Therefore, a need exists for a feasible testing paradigm to obtain robust measures of foot placement to investigate foot placement control.
Current gait rehabilitation programs and measures are mainly focussed on walking speed (Dickstein, 2008). However, being able to walk fast does not necessarily mean improved quality and safety of walking. Recently, many studies are investigating feasibility and success of gait adaptability training (Heeren et al., 2013; K. L. Hollands et al., 2015; Timmermans et al., 2016; van Ooijen et al., 2015; van Ooijen et al., 2013). Multiple attempts have been made to investigate the mechanisms limiting gait adaptability by target stepping when walking. In these studies multiple methods and measures have been used to asses stepping accuracy. Stepping from standing (Nonnekes et al., 2010; Reynolds & Day, 2005a), over ground walking to targets (K. L. Hollands et al., 2016; Lindemann et al., 2013) and treadmill walking to targets (Hoogkamer et al., 2015; Mazaheri et al., 2015; Mazaheri et al., 2014; Peper et al., 2015). Target stepping paradigms have been used mainly with healthy adults, using various outcome measures such as walking speed (K. L. Hollands et al., 2016; Lindemann et al., 2013), task success (K. L. Hollands et al., 2016; Hoogkamer et al., 2015), stepping error normalized to step length (Mazaheri et al., 2015), variable error (Lindemann et al., 2013; Mazaheri et al., 2014) and absolute error (Nonnekes et al., 2010; Reynolds & Day, 2005a). This great spread of methodologies and use of measures makes it complicated to
compare results and gain definite understanding of limitations of foot placement control in stroke survivors, but also in other populations that are prone to falls.
Current evidence (reviewed in Chapter: Literature review) indicates that stroke survivors may have difficulty adapting their foot placement in response to the environment. Several studies have documented that, similar to healthy older adults, stroke survivors prefer to lengthen rather than shorten their steps when avoiding obstacles (Den Otter et al., 2005; van Swigchem et al., 2013). Stroke survivors hit more obstacles, which means they are less successful, than healthy adults when the obstacles appear with limited response time; at the time of transition from stance to swing of the avoiding leg (Den Otter et al., 2005; van Swigchem et al., 2013). The preference for step lengthening rather than shortening and a decline in performance under time pressure have also been seen in healthy young adults during target stepping while walking (Hoogkamer et al., 2015). Nonnekes et al. (2010) found narrowing foot placement targets had large foot placement errors in stroke survivors. So, evidence indicates that stroke survivors may have diminished ability to adapt foot placement in some directions; particularly narrowing steps and especially under time pressure, as Den Otter et al. (2005) and van Swigchem et al. (2013) showed success declined with time pressure. Therefore, foot placement accuracy in stroke survivors is likely to be affected by the direction of adaptation and the available response time more so than in healthy young and older adults.
In the present study, the first aim is to test feasibility and robustness of the current target stepping paradigm. Secondly, this study evaluates foot placement for reactive and planned conditions as the direction of foot placement adjustment during walking. How stroke survivors and healthy adults make step length and width adjustments under time pressure. The data from this study will give a strong basis for completing a powered study to test target stepping; providing more insight in how stroke survivors adapt their gait and what factors limit accurate foot placement adaptation during walking.