10 Chapter 1 the base of support), and 2) ankle strategies (i.e., ankle moments of the stance leg are modulated to make (minor) adjustments to center of mass movements). When both strategies are hindered, 3) hip strategies can be used (i.e., upper body segments are rotated around the center of mass).18 Several methods then exist to objectify dynamic balance. In clinical practice, this is often done as part of clinical tests that assess balance capacity (e.g., with the Mini Balance Evaluations Systems Test). More recently, there is growing interest in the use of biomechanical measures that assess dynamic balance or ‘gait stability’. Gait stability measures often require sophisticated motion capture systems and complex calculations.19 In this thesis, we refer to the following measures of gait stability: gait variability, margin of stability, foot placement deviation, and Lyapunov exponents (for a detailed description – see box 1). Gait adaptability Finally, people require adaptive capabilities during gait, so that the stepping pattern can be altered to meet environmental demands. Nine domains have been identified that necessitate gait adaptability: (1) obstacle negotiation (e.g., alter step length to step over a loose tile), (2) temporal demands (e.g., slowing down in a busy street), (3) cognitive dual-tasking (e.g., engaging in a conversation while walking), (4) terrain demands (e.g., walking over uneven surfaces), (5) ambient demands (e.g., lighting or familiarity with the surroundings), (6) postural transitions (e.g., turning while walking), (7) motor dual-tasking (e.g., manipulating a phone while walking), (8) physical load (e.g., carrying a bag), and (9) maneuvering in traffic.17 It is evident that gait adaptability is of high importance for safe and independent ambulation in the community.17 Gait adaptability can be assessed using clinical tests, such as the obstacle subtask of the Emory Functional Assessment Profile (E-FAP)20,21, or the recently developed Walking Adaptability Ladder test for Kids (WAL-K).22
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