Abstract
BACKGROUND: Advanced footwear technologies (AFT) are popular for their potential performance benefits, though concerns about injury risks persist. Among various AFT features, sole thickness is particularly debated, especially after World Athletics imposed a 40 mm limit to prevent unfair competitive advantages. However, the effects of sole thickness on running biomechanics and economy are not well understood, particularly because sole thickness often co-varies with other shoe characteristics in shoe designs. OBJECTIVE: This review examines the effects of sole thickness on spatiotemporal variables, kinematics, kinetics, and running economy. The review focuses on studies in which sole thickness was the primary variable of interest. METHODS: A systematic literature search was conducted following PRISMA guidelines. Eligible studies included original research on running with participants of all expertise levels, analyzing spatiotemporal variables, kinematics, kinetics, or running economy. RESULTS: Fourteen studies met the criteria, mostly focusing on male recreational or experienced runners. Thicker soles were linked to increased stance time, while other spatiotemporal parameters remained unchanged. Significant effects were seen in ankle kinematics, with more dorsiflexion at initial contact with thicker soles, though knee and hip movements were less affected. Thicker soles increased peak eversion in the frontal plane. No consistent trends emerged for joint kinetics, stiffness, or center of mass movement. Vertical ground reaction force (GRF) peaks remained largely unchanged, but loading rates generally decreased with thicker soles. Only one study assessed running economy, with no significant effects. Overall, the certainty of evidence across outcomes was low to very low due to methodological heterogeneity and limited study numbers. CONCLUSIONS: Thicker soles were largely linked to longer stance times and lower GRF loading rates. Future research should comprehensively report shoe characteristics, include more diverse populations (e.g., female runners, forefoot strikers), and expand investigations to underexplored aspects such as muscle activity and movement coordination.