Curved carbon-plated shoe may further reduce forefoot loads compared to flat plate during running

Abstract

Using a curved carbon-fiber plate (CFP) in running shoes may offer notable performance benefit over flat plates, yet there is a lack of research exploring the influence of CFP geometry on internal foot loading during running. The objective of this study was to investigate the effects of CFP mechanical characteristics on forefoot biomechanics in terms of plantar pressure, bone stress distribution, and contact force transmission during a simulated impact peak moment in forefoot strike running. We employed a finite element model of the foot-shoe system, wherein various CFP configurations, including three stiffnesses (stiff, stiffer, and stiffest) and two shapes (flat plate (FCFP) and curved plate (CCFP)), were integrated into the shoe sole. 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. 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). We concluded that employing a curved CFP in running shoes could be more beneficial from an injury prevention perspective by inducing less peak pressure under the metatarsal heads while not worsening their stress state compared to flat plates.

Figure 1

Comparison of plantar pressure in foot-shoe models with respect to different CFP shapes and stiffnesses at the impact peak instant during FFS running. (a) Depicts the results of the finite element analysis while (b) shows the peak plantar pressure values of each condition.

Figure 2

Comparison of MTP joint contact force transmission in foot-shoe models with respect to different CFP shapes and stiffnesses at the impact peak instant during FFS running, (a) Medial path of the MTP joint contact force transmission; (b) Lateral path of the MTP joint contact force transmission; (c) Anatomical schematic illustration of the MTP joint contact force transmission. Force is depicted in terms of times of body weight. Blue arrows are for foot-shoe model without CFP, red arrows are for foot-shoe models with FCFP, and green ones are for foot-shoe models with CCFP. The gradation in coloration represents the variations of CFP thickness. Specifically, the lighter the shading, the greater the thickness of the CFP.

Figure 3

(a) Configurations of the different foot-shoe models with respect to different CFP shapes and thicknesses, including no CFP (NCFP, stiffness: 2.19 N/mm), 1 mm-flat CFP (FCFP1, stiffness: 6.25 N/mm), 2 mm-flat CFP (FCFP2, stiffness: 16.36 N/mm), 3 mm-flat CFP (FCFP3, stiffness: 46.25 N/mm), 1 mm-curved CFP (CCFP1, stiffness: 6.25 N/mm), 2 mm-curved CFP (CCFP2, stiffness: 16.36 N/mm), 3 mm-curved CFP (CCFP3, stiffness: 46.25 N/mm); (b) Subject-specific musculoskeletal model and simulation of the forefoot running gait; (c) Boundary and loading conditions for the finite element analyses. The LBS of the plate was calculated by simulating the flexion mechanical test.