Classification of medial longitudinal arch kinematics during running and characteristics of foot muscle morphology in novice runners with pronated foot

Background: Novice runners with pronated feet are at an increased risk of running-related injuries. However, not all runners with pronated feet have increased foot pronation during running. Moreover, although foot muscle morphology is related to static foot alignment, the relationship between foot muscle morphology and foot kinematics during running remains unclear. We aimed to determine foot kinematic patterns during running among novice runners with pronated feet and the presence of a relationship between these foot kinematic patterns and foot muscle morphology.

Methods: Twenty-one novice runners with pronated feet participated in this study, and data on 39 lower limbs were collected. Data on foot kinematics during running (rearfoot strike) were collected using a three-dimensional motion capture system in terms of navicular height (NH) at initial contact and dynamic navicular drop (DND). A hierarchical cluster analysis method was used to identify the optimal number of clusters based on these two foot-related kinematic variables. Following identification of the clusters, differences in cluster variables and cross-sectional areas of selected foot muscles assessed using ultrasonography in each cluster were examined. The muscles of interest included the abductor hallucis, flexor hallucis brevis and longus, flexor digitorum brevis and longus, and peroneus longus.

Results: Three subgroups were identified based on foot kinematics during running: cluster 1, lowest NH at initial contact and larger DND; cluster 2, moderate NH at initial contact and smaller DND; and cluster 3, highest NH at initial contact and larger DND. Clusters 1 and 3 had a larger abductor hallucis compared with cluster 2, and cluster 3 had a larger flexor hallucis brevis compared with cluster 2.

Significance: These subgroups may differ in terms of resistance to and type of running-related injury. Moreover, foot kinematics during running is possibly impacted by the morphology and function of medial intrinsic foot muscles.