Learning to cope with trips: retention and generalisability of fall-resisting skills across the adult lifespan

Daily-life locomotion constantly challenges our neuromotor system, requiring adjustments in motor strategies to cope with external perturbations (e.g. a trip), control stability and avoid falls. Though knowledge about the effectiveness of perturbation-based interventions for improving fall-resisting skills in older adults has grown considerably, the effects of age and different protocol parameters on the adaptability (i.e adaptation, retention, generalisability) of the balance control system are not well established. This dissertation examined the adaptability and specificity of fall-resisting skills across the adult lifespan, with the perspective that the insight gained could improve both the effectiveness and efficicency of the assessment and training of fall-resisting skills. Four studies were conducted, comprising of both cross-sectional and longitudinal (14 weeks) designs. The first part of the dissertation focused on the specificity of the assessment of reactive dynamic stability control and the second part on adaptability to trip-perturbation exposure and how this varies with practice dose or age (i.e. young, middle-aged, old). Firstly, a gradual, age-related decline in reactive stepping performance was confirmed for different stepping modes. More importantly, it appears that volitional stepping characteristics have limited potential for discriminating between individuals or groups with quite different balance recovery capabilities. Therefore, volitional stepping tasks may not be sensitive enough for clinical application. Secondly, although the adaptability of reactive gait stability control during a single bout of trip-perturbations remains highly effective across the adult lifespan (which could counteract the initially poorer ability to cope with sudden balance loss in older age), retention of these improvements over several months seems to be diminished with ageing and dependent on a specific number of perturbations. Finally, the robust adaptations in stability control could not benefit recovery performance in an untrained reactive balance task, suggesting task specificity of learning. Profound differences in the spatiotemporal organisation of muscle activation patterns, i.e. muscle synergies, indicate a diverging modular control to different perturbations, possibly preventing inter-task generalisation of adaptations in stability control.