107 Summary and general discussion to differentiate between fallers and non-fallers with HSP (chapter 6). Against this background, the added value of the proposed biomechanical measures to assess dynamic balance for clinical or research purposes in people with HSP has yet to be determined. The assessment of gait adaptability requires context-specific tasks that reflect the expected and unexpected demands of everyday walking in the community. These tasks include crossing over unexpected physical objects, performing motor and cognitive dual tasks, participating in traffic, changing gait speed, et cetera. Including all these tasks in one clinical test is unfeasible, but some tests that assess at least various aspects of gait adaptability are available. The obstacle subtask of the Emory Functional Ambulation Profile has previously been used 14,15 and includes the components of obstacle avoidance and temporal demands. We additionally used the newly developed ‘walking adaptability ladder test’ (WALT), which includes precision stepping and temporal demands. Furthermore, the subtest ‘dynamic gait’ of the Mini-BESTest incorporates cognitive dual-tasking, motor dual-tasking, obstacle avoidance, and temporal demands. All these clinical tests are standardized, quick, and require few or no attributes at all, which makes them feasible for clinical practice. Yet, a common limitation of these tests is that the testing environment is known to the participant, i.e., the tests do not include unpredictable perturbations. Such unpredictable perturbations, however, are common when walking in daily life, such as tripping over obstacles, slipping on a wet surface, or being bumped by someone in a crowd. Some tests have addressed these limitations and assessed ‘online’ gait adaptability requiring adaptation of ongoing pre-planned movements. Examples are the Interactive WalkWay (a walkway that uses augmented reality to project unexpected obstacles onto the floor16,17) and instrumented obstacle avoidance (a task in which a physical obstacle is released from an electromagnet onto a treadmill at various moments of the gait cycle18,19). Including unexpected perturbations in clinical testing is valuable but challenging, as these tests require sophisticated equipment. ‘Online’ gait-adaptability testing in people with HSP is currently relatively unexplored. Gait performance To assess whether people actually do what they are able to do, it is important to evaluate daily life gait performance. Compared to the ‘snapshot’ evaluation of gait capacity, gait performance provides a more ecologically valid assessment associated with real life. 2,20 Within this thesis, we included Activ8 monitors to provide insight into how much time participants were physically active during 24 hours. 21 However, activity monitoring is still poorly validated in people with HSP. Furthermore, the Activ8 monitors are limited to identifying specific postures (standing, sitting, lying) and (the intensity of) specific activities (walking, running, cycling). This results in two 7
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