Coherence in Foot Mechanics: Principles and Applications Across Biomechanics and Design

This paper introduces a coherence-based framework for understanding foot mechanics as a nonlinear, multiscale system. Rather than analysing foot function through isolated anatomical components or peak external loading metrics, the framework emphasises coordinated deformation, load sharing, and regime-dependent behaviour across bones, joints, soft tissues, and interfaces. Mechanical coherence is defined as the preservation of stable relationships between force transmission, tissue deformation, and stiffness modulation across space and time. Within coherent operating regimes, the foot accommodates load through distributed, repeatable deformation. Loss of coherence—whether through excessive stiffness, excessive compliance, or spatially localised overstressing—can compromise durability and function even when external force measures appear unchanged. By integrating evidence from biomechanics, plantar tissue mechanics, pressure distribution, and interface design, the paper reframes longstanding debates in locomotion and footwear research. Variability in experimental outcomes is interpreted as an intrinsic feature of nonlinear biological systems rather than as noise or contradiction. The framework provides a principled explanation for why categorical prescriptions and single-parameter optimisation strategies often fail to generalise across individuals and contexts. The implications of mechanical coherence extend beyond footwear biomechanics to prosthetic interfaces and wound prevention, where long-term tissue integrity depends on preserving coordinated load distribution rather than minimising force magnitude alone. By offering a system-level interpretive lens, this work provides a foundation for future research and design approaches that respect the constraints of biological materials while accommodating individual and task-specific variability.