Multiscale Biomechanical Analysis of Running: Inter- and Intraindividual Variability with Insights into Second...

Variability in running plays a crucial role in distributing biomechanical loads and can be consequently associated with injury risk. This study aims to compare the level of variability between several biomechanical features at different scales of analysis, to investigate the correlations in amplitude and variability between biomechanical features and the second metatarsal stress, and to explore the inter- and intraindividual variability of the stress distribution in the second metatarsal.

Eight participants looped overground on a 45-m circuit for 30 min, while kinematics, kinetics, and plantar pressure of a stance phase were recorded at each loop. A dynamic finite element model of the foot, driven by muscle forces estimated by a musculoskeletal model, was used to estimate internal loads in the foot. Each variable of interest was classified into a category [ground reaction force (GRF), angles, net joint moments, muscle forces, joint reaction forces, and internal bone stress]. Variability was quantified using the mean standard deviation over the stance phase and compared both within and between these categories.

The study revealed that variability across biomechanical domains of analysis lacked a clear relationship, with GRF components showing the lowest variability and joint angles exhibiting the highest. Although second metatarsal stress amplitude correlated strongly with vertical GRF, joint moments, and muscle forces, its variability showed less consistent correlations and was more participant-dependent. Significant inter/intra individual variations in second metatarsal von Mises stress amplitude and variability were observed.

External GRFs and joint kinematics-related quantities, extracted directly from the experimental data, were found to inadequately represent the internal load variability, thus questioning the representativeness of these external features to assess internal stress/load variability.