Running-Induced Fatigue Changes the Structure of Motor Variability in Novice Runners

Abstract

Understanding the effects of fatigue is a central issue in the context of endurance sports. Given the popularity of running, there are numerous novices among runners. Therefore, understanding the effects of fatigue in novice runners is an important issue. Various studies have drawn conclusions about the control of certain variables by analyzing motor variability. One variable that plays a crucial role during running is the center of mass (CoM), as it reflects the movement of the whole body in a simplified way. Therefore, the aim of this study was to analyze the effects of fatigue on the motor variability structure that stabilizes the CoM trajectory in novice runners. To do so, the uncontrolled manifold approach was applied to a 3D whole-body model using the CoM as the result variable. It was found that motor variability increased with fatigue (UCM_ꓕ). However, the UCM_Ratio did not change. This indicates that the control of the CoM decreased, whereas the stability was not affected. The decreases in control were correlated with the degree of exhaustion, as indicated by the Borg scale (during breaking and flight phase). It can be summarized that running-induced fatigue increases the step-to-step variability in novice runners and affects the control of their CoM.

Keywords: biomechanics; center of mass; motor control; uncontrolled manifold (UCM).

Figure 1

Time courses for UCM_ꓕ (light-red and light-blue lines) and UCM_‖ (dark-red and dark-blue lines), PRE (solid lines) and POST (dashed lines) fatigue. The perpendicular black lines show the gait events right toe off (RTO), left foot strike (LFS) and left toe off (LTO). Solid lines are the gait events PRE fatigue, and dashed lines are the gait events POST fatigue.

Figure 2

Results for the three dependent UCM parameters. From top to bottom: UCM_ꓕ, UCM_‖ and UCM_Ratio. The solid red line shows the results PRE fatigue, and the dashed blue line shows the results POST fatigue. The perpendicular black lines show the gait events right toe off (RTO), left foot strike (LFS) and left toe off (LTO). Solid lines are the gait events PRE fatigue, and dashed lines are the gait events POST fatigue. Significant differences are highlighted in grey.