Effects of a Fatigue Protocol on Vertical, Leg, and Joint Stiffness during Overground Running

Abstract

Running-induced neuromuscular fatigue can alter spring-mass characteristics such as vertical, leg, and joint stiffness. The purpose of the study was to investigate the effects of a treadmill run fatigue protocol on stiffness parameters during overground running. Sixteen healthy cadets (22.4 ± 3.9 yr, 1.76 ± 0.08 m, 72.4 ± 12.3 kg) from a University’s Army Reserve Officer Training Corp were included in the study. Rested and exhausted state overground running biomechanics were collected prior to and immediately after a fatigue protocol that involved an Åstrand Protocol Graded Exercise Test and an exhaustive run at a velocity associated with 80% VO2max. No significant changes were observed for vertical, leg, or joint stiffness group means. While insignificant, knee stiffness displayed increasing trends while hip stiffness displayed decreasing trends. Leg length at initial contact (-1%, p = 0.007) and compressed leg length (-1%, p = 0.013) significantly decreased. Hip excursion (+9%, p = 0.021), change in knee moment (+7%, p = 0.027), and knee moment at the instance when the anterior- posterior ground reaction force was zero (+8%, p = 0.021) significantly increased. While running in a fatigued state, subjects attempted to maintain overall vertical and leg stiffness with joint stiffness modulations.