Relationship Between Foot Flexibility and Leg Muscle Stiffness After Running: a Cross-sectional Study

Abstract

BackgroundDeformation of the foot is related to the development of running injuries. The prevention of running injuries requires the management of changes in leg muscle stiffness after running. However, the relationship of muscle stiffness and the structure and flexibility of the foot arch is unclear. The purpose of this study was to investigate differences in muscle stiffness and flexibility of the arch before and after running.MethodsTwenty lower limbs of 10 healthy volunteers were enrolled. All of the subjects performed the same running task on a treadmill set at an incline of 7%, running at a speed of 8 km/h for 60 min. The shear elastic modulus of the longitudinal axis of the medial and lateral gastrocnemius (MG, LG), flexor digitorum longus (FDL), and abductor hallucis muscles were measured both before and after running using ultrasound shear wave elastography. Arch height index (AHI) and arch height flexibility (AHF) were measured at 10, 50, and 90% of the body weight loaded position, respectively. The correlation of AHI, AHF, and alterations in each muscle stiffness before and after running was assessed using Spearman’s rank correlation coefficient.ResultsThe FDL, LG, and MG were significantly harder after running than before running. The AHI and AHF had no significantly difference between before and after running. There were significant moderate correlations between AHF50 before running and stiffness of the FDL after running.ConclusionIncreased stiffness of the FDL is related to medial tibial stress syndrome. Our results indicate that stiffness of the arch is associated with greater stiffness of the FDL, which restricts performance of the dynamic function of stretching the muscle and tendon complex of the toe flexor with weight loading on the foot.