Author(s): SONG, Y., WANG, M., CEN, X., SUN, D., BÁLINT, K., GU, Y., ZHANG, M., WANG, Y., Institution: THE HONG KONG POLYTECHNIC UNIVERSITY, Country: CHINA, Abstract-ID: 697

INTRODUCTION:
Long-distance running is known to cause foot pain and injuries due to repetitive loading. One potential solution to reduce foot injury risk is using carbon-fiber plates (CFP) in footwear, which may alleviate forefoot pain by offloading this area [1]. However, the effectiveness of CFP footwear may vary depending on its design features [2, 3]. Thus, the aims of this study were to 1) develop a 3D foot-shoe coupled FE model that can be used to reveal the internal foot mechanics; 2) compare the load changes on plantar tissue and metatarsal bones under different CFP modifications at the impact peak during forefoot running.
METHODS:
A male recreational runner (age: 27 years, height: 175cm, mass: 70kg) was involved. Using his medical CT images, all major foot and shoe structures were reconstructed. The foot model included 20 bones, 5 plantar fasciae, 66 ligaments, and an encapsulated soft tissue. Cartilage function was resembled by a frictionless contact algorithm without reconstructing its geometry. A custom running shoe was reconstructed to represent the control condition, with various CFP configurations (three stiffness levels: stiff, stiffer, stiffest; two shapes: flat plate (FCFP) and curved plate (CCFP)) integrated into the shoe sole. Running biomechanics in sagittal plane, including foot-ground angle, MTP joint contact force, Achilles tendon force as well as vertical ground reaction force, were calculated for finite element analyses. A quasi-static contact approach was utilized to simulate the impact peak instant during forefoot running.
RESULTS:
Comparing the shoes with no CFP (NCFP) to those with CFP, we consistently observed a reduction in peak forefoot plantar pressure with increasing CFP stiffness. This decrease in pressure was even more notable in a CCFP demonstrating a further reduction in peak pressure ranging from 5.51% to 12.62%, compared to FCFP models. Both FCFP and CCFP designs had a negligible impact on reducing the maximum stress experienced by the 2nd and 3rd metatarsals (less than 3%). However, they greatly influenced the stress distribution in other metatarsal bones. These CFP designs seem to optimize the load transfer pathway, enabling a more uniform force transmission by mainly reducing contact force on the medial columns (the first three rays, measuring 0.333 times body weight for FCFP and 0.335 for CCFP in stiffest condition, compared to 0.373 in NCFP).
CONCLUSION:
It is concluded that a running shoe equipped with a CCFP may offer greater potential for overuse injury prevention. Such a design leads to reduced peak pressure under the forefoot without notably impacting the stress state of the metatarsal bones, as compared to the NCFP and FCFP conditions. Employing a CFP with appropriate stiffness, in general, appears to redirect the load transfer pathway toward a more evenly distributed force transmission, potentially mitigating the risk of overuse injuries during long-distance running.
1. Stefanyshyn et al. (2016) 2. Flores et al. (2019) 3. Song et al. (2023)