Ecological gait dynamics: stability, variability and optimal design

Abstract

Variability–stability relationships are the very foundation of flexible biological movements. For footwear design, stability is best defined as pattern stability at the level of segmental relationships with regard to goal-oriented performance. Footwear design should seek to optimize the variation in segmental relationships while maintaining the overall locomotion pattern, providing a system that is both adaptable to upcoming events and stable to unanticipated perturbations. As footwear is designed for a variety of uses other than forward, continuous running on a flat terrain, an examination of the fundamental assumptions and applicability of traditional gait dynamics is necessary. Expanding evaluation of gait dynamics to non-forward, non-continuous motion across different terrains would seem appropriate, given the ubiquity of these movements in everyday life. Optimizing footwear design for different tasks requires trade-offs between design and material selection and a principled scientific approach to understanding these trade-offs is required. Evaluation of these non-traditional gait dynamics and incorporation of goal-oriented performance requires consideration of the behavioural consequences of design and perception–action coupling. Understanding variability–stability relationships remains at the center of any attempt to understand footwear performance and design implications in these expanded gait dynamics. The basis for changing historical perspectives on variability–stability relationships is discussed with regard to maintaining and changing coordinative patterns, information–movement relationships, injury prevention, and optimizing performance through footwear design. A principled approach to building a footwear performance space from empirical data is provided, and it is suggested that such an approach offers objective metrics for making appropriate trades in footwear design to optimize performance across categories of intended use.