Study on the Biomechanical Mechanism of Foot Bruised Toenail Injury Caused by Long-Distance Running

Objective: To determine the potential effect of foot morphology changes on the injury risk of bruised toenail during longdistance running, and to further optimize the design of running shoe structure and comprehensively verify its effects on preventing bruised toenail injury. Methods: Ten male recreational runners participated in this study, the foot morphology, foot temperature,perceived comfort, and the gap length in the sagittal plane were collected at before（baseline）, immediately after 5 km and 10 km of treadmill running. In addition, the design of toe box was optimized based on the biomechanical mechanism of foot bruised toenail injury, where the original shoes has a toe height of 65.8 mm and a length of 85.5 mm; the new-designed shoes has a toe height of 79.5 mm and a length of 85.8 mm. The comfort perception, foot-shoe contact forces, and contact pressure were collected across different running shoes to confirm the effectiveness of injury prevention. Results: The width of forefoot and arch height were reduced greatly after the 10 km run. Foot temperature was increased significantly after 5 km and 10 km running, and the temperature of dorsal hallux was significantly higher after 10 km running than that of 5 km run. Regarding to the hallux comfort, the perceived score was significantly reduced after 5 km and 10 km running. In addition, there was a significant increase in gap length after 10 km running during one running gait cycle, followed by a notable decrease upon reaching midstance. Compared with the original shoes,the subjective comfort of new-designed shoes was increased, and the new-designed shoes significantly reduced the force during the contact phase by 0～80% and achieved a more uniform pressure distribution. Conclusions: The reduced width of forefoot and arch height, increased foot temperature, accompanied by the decreased subjective comfort and increased gap length during long-distance running would potentially responsible for bruised toenail injuries. Meanwhile, running shoes designed with an elevated toe box increased subjective comfort while reduced contact force and achieved a more uniform pressure distribution, which could reduce the risk of bruised toenail injury effectively.