EMG Signal Shifts During Repeated Isokinetic Knee Movements In Elite Badminton Athletes

Abstract

PURPOSE: To elucidate the torque decline and EMG varieties when the badminton athletes were performing the maximal 50-time repeated maximal isokinetic knee movement. METHODS: 9 male badminton athletes was conducted (18.8 ± 1.6 years,175.9 ± 7.16 cm,71.0 ± 8.8 kg) to perform 50-time repeated maximal voluntary knee extension and flexion at a constant velocity (180 degree/s-1 or 3.14rad/s-1), using the Biodex equipment. The torque and EMG signals were recorded at the same time, and use the power spectral density function to analyze the torque decline percentage, rectus femoris EMG-RMS (root mean square), and the mean power frequency (MPF) of maximal knee extension. All the dependent variables were using One-Way ANOVA to analyze the differences. RESULTS: (1) from the maximal knee extension torque: the torque followed the contraction times gradually decrease, and both the first 5 and last 5 torques are 84.6 ± 16.9 Nm and 68.9 ± 19.6 Nm respectively, and the torque is decline at 19% in all performances. (2) In the RMS: even though the RMS is increasing gradually in the initial phase (first contraction to the tenth) significantly (P <.05), there is no further decreases occurred in the after (P >.05; first 5 contraction RMS=0.65 ± 0.25 mV, last 5 contraction RMS=0.61 ± 0.17 mV). (3) In the MPF section, it was decreasing from one to fifty contraction (P <.05; first 5 contraction MPF=86.3 ± 7.93 Hz,last 5 contraction MPF=61.6 ± 7.74 Hz). CONCLUSIONS: (1) When these badminton athletes were performing maximal voluntary isokinetic contraction, the EMG-RMS doesn't change in the follows contraction times, but the MPF (decrease 25 Hz) and torque (decrease 16 Nm) were decreasing significantly. It may reflect that the lactate accumulation and other metabolites make the type I muscle fiber fatigue faster. (2) Compare to other researches, they found that the torque in athletes (soccer, basketball, and others...) or the untrained subjects to perform 30-50 times knee extension is decline 41% (Kawabata et al., 2000; Pincivero et al., 2003). The decline percentage is more than out research 19%. It may reflect that the badminton athletes' lower limb have higher resistance ability. In the future, investigator can consider the mechanism about the characteristic.