Effects of Fatigue on Knee Joint Movement Complexity Based on Sample Entropy During Running in Semi-Professional Soccer Players

IntroductionFootball is a highly dynamic sport in which the lower limbs are exposed to substantial mechanical loads, and fatigue is recognized as a key factor influencing motor control strategies and injury risk. However, limited evidence exists regarding the effect of fatigue on the nonlinear dynamics and complexity of knee joint kinematics in semi-professional football players. Therefore, the present study aimed to investigate the effect of fatigue on lower-limb movement dynamics during running using sample entropy analysis of knee joint position time series.MethodsThis semi-experimental study employed a one-group pre-test–post-test design. Sixteen semi-professional male football players (mean age: ۱۹.۵ years) were recruited through convenience sampling. Three-dimensional kinematic data were collected using a Rapture H motion capture system with six infrared cameras operating at ۲۳۰ Hz. Participants performed treadmill running at a speed of ۱۰.۸ km/h under pre-fatigue and post-fatigue conditions. Fatigue was induced using the Köbelbauer protocol. Sample entropy was calculated from knee joint position time series to quantify movement complexity and irregularity.ResultsPaired t-test analysis revealed a statistically significant increase in sample entropy after fatigue (pre-fatigue: ۰.۱۷; post-fatigue: ۰.۱۸; p = ۰.۰۲۶). Although this increase was statistically significant, the magnitude of change was small, indicating minimal practical alteration in the running pattern.Discussion and ConclusionThese findings suggest that fatigue induces only slight changes in the complexity of knee joint kinematics in semi-professional football players. The neuromuscular system likely employs compensatory mechanisms to preserve the stability and rhythmic structure of running under fatigue conditions. Overall, the results highlight that statistical significance does not necessarily correspond to functional significance. Furthermore, sample entropy can serve as a useful nonlinear tool for complementary assessment of movement control in sports biomechanics

کلیدواژه ها:

fatigue ، sample entropy ، nonlinear dynamics ، knee joint ، running ، semi-professional football players