Effect of Quadriceps Muscular Fatigue on Knee Joint Kinetics at Different Flexion/Extension Velocities in Male Soccer Players

The purpose of the current study was to investigate the effect of quadriceps muscular fatigue on knee joint kinetics and kinematics in professional soccer players.
In the present semi-experimental study, 20 male soccer players (age: 22.90±2.29 years) volunteered to participate. Isokinetic dynamometer (Gymnex ISO 2) was used to measure biomechanical variables during 60, 180, and 360 degree/s angular velocities, each including three repetitions of different flexion/extension velocities. Shapiro-Wilks goodness-of-fit test was used for normality and paired samples t-Test and Two-Way analysis of Variance were used for data analysis (p<0/05).
The results showed that there was a significant reduction in the peak extensor power in angular velocity of 60 degrees/s after fatigue as compared to before fatigue (p=0.002). Also, there was significant effects of velocity factor on peak extensor torque (P<0.001), peak flexor torque (P<0.001), peak extensor ratio torque (P<0.001), peak flexor ratio torque (P<0.001), peak extensor angle torque (P=0.048), peak extensor power (P=0.001), peak flexor power (P=0.003), peak extensor work (P<0.001), peak flexor work (P<0.001), total extensor work (P<0.001), total flexor work (P<0.001), and ratio Flexor strength to Extensor (P<0.001).
Our results demonstrated that peak extensor power in 60 degrees/s reduced after fatigue. Reduction of peak extensor power could be a possible reason of reduction of performance in the final parts of the competition.