Author(s): ZHANG, Q., CHEN, S.Q., LI, F., MA, H.F., Institution: SHANGHAI UNIVERSITY OF SPORT, Country: CHINA, Abstract-ID: 1090

INTRODUCTION:
Stiffness, originally derived from "Hooks Law," is defined as the ratio between the external force and the deformation displacement applied to a spring system, reflecting the systems elastic performance and its ability to accumulate elastic potential energy. In running, higher lower-limb stiffness is beneficial for the storage and release of elastic energy, thus improving running economy. Knee and ankle joint stiffness are considered determining factors of lower-limb stiffness. Meanwhile, during the ground contact phase of running, the muscles around the knee and ankle joints contract synergistically to produce force and regulate the joint stiffness. Therefore, joint muscle strength may play an important role in regulating joint stiffness. This study aims to explore the correlation between isokinetic knee and ankle joint strength and knee and ankle joint stiffness in recreational runners.
METHODS:
Thirty-four male runners were recruited to measure knee and ankle joint stiffness at running speeds of 10 and 12 km·h-1 by the Vicon 3D motion capture system and the Kistler 3D force platforms mounted below the treadmill belt. The isokinetic strength test and training system was used to measure isokinetic knee and ankle joint concentric and eccentric peak torque (PT) at the velocities of 60 and 180°·s-1. Pearson correlations, with the Benjamini–Hochberg correction procedure, were used to analyze the correlation between isokinetic knee joint PT and knee joint stiffness, and the correlation between isokinetic ankle joint PT and ankle joint stiffness.
RESULTS:
For knee joint, the knee flexor eccentric PT at 60°/s (P<0.001, r=0.614; P<0.001, r=0.592) and 180°/s (P<0.001, r=0.582; P<0.01, r=0.558) was highly positively correlated with knee stiffness at 10 and 12 km·h-1. The knee flexor concentric PT at 60°·s-1 (P<0.05, r=0.417; P<0.05, r=0.404) and 180°·s-1 (P<0.05, r=0.440; P<0.05, r=0.396) was moderately positively correlated with knee stiffness at 10 and 12 km·h-1. For ankle joint, the ankle dorsiflexor eccentric PT at 60°·s-1 (P<0.05, r=0.460; P<0.05, r=0.523) was positively correlated with ankle joint stiffness at 10 and 12 km·h-1.
CONCLUSION:
knee and ankle stiffness during running may be associated with greater knee flexor and ankle dorsiflexor strength, which would inform muscle strength modulation of lower-limb joint stiffness to improve running performance.