Changes in ground reaction forces, joint mechanics, and stiffness during treadmill running to fatigue

Abstract

Purpose: This study aimed to determine the changes in lower extremity biomechanics during running-induced fatigue intervention. Methods: Fourteen male recreational runners were required to run at 3.33m/s until they could no longer continue running. Ground reaction forces (GRFs) and marker trajectories were recorded intermittently every 2 min to quantify the impact forces and the lower extremity kinematics and kinetics during the fatiguing run. Blood lactate concentration (BLa) was also collected before and after running. Results: In comparison with the beginning of the run duration, (1) BLa significantly increased immediately after running, 4 min after running, and 9 min after running; (2) no changes were observed in vertical/anterior-posterior GRF and loading rates; (3) the hip joint range of motion (θROM) significantly increased at 33%, 67%, and 100% of the run duration, whereas θROM of the knee joint significantly increased at 67%; (4) no changes were observed in ankle joint kinematics and peak joint moment at the ankle, knee, and hip; and (5) vertical and ankle stiffness decreased at 67% and 100% of the run duration. Conclusion: GRF characteristics did not vary significantly throughout the fatiguing run. However, nonlinear adaptations in lower extremity kinematics and kinetics were observed. In particular, a "soft landing" strategy, achieved by an increased θROM at the hip and knee joints and a decreased vertical and ankle stiffness, was initiated from the mid-stage of a fatiguing run to potentially maintain similar impact forces.