It was studied the effect of fast knee extension exercises with different intensity on the MPF decline rate of quadriceps sEMG signal and the descending rate of knee extensor average output power, as well as their correlation, the central control theory of dynamic muscle movement was also disscussed.17 male college student participations completed 30 pedal movement with the fastest speed under the leg load of 105.8, 140.9, 176.4 kg, respectively, sEMG signals, time and distance of quadriceps′actions were collected.The effect of 3 loads on MPF and output power of quadriceps ( lateral) , quadriceps ( medial) and rectus femoris were also detected.The results showed that MPF of sEMG signals declined with the exercises number under different intensity of knee extension exercises, which was consistent with the previous static investigation.MPF descending slopes had no difference, while the descending slopes of average output power were different.Av-erage output power of 3 different loads had trends of rising, constant and decreasing respectively.%为研究不同强度快速伸膝运动对股四头肌群表面肌电信号（ surface electromyography，sEMG）的平均功率频率（ mean power frequency，MPF）下降率和伸膝平均输出功率下降率的影响及相关性，探讨了动态肌肉运动的中枢控制理论，以17名男性大学生为研究对象，让他们下肢负荷分别为105．8，140．9，176．4 kg时，以最快速度完成30次蹬踏运动．采集股四头肌sEMG信号和每次动作时间、距离，考察了3种负荷对股四头肌（外侧）、股四头肌（内侧）和股直肌MPF及输出功率的影响．结果显示：不同强度快速伸膝运动下股四头肌sEMG信号MPF随次数而下降，与以往静态研究相一致；MPF下降斜率没有差异；平均输出功率下降斜率有差异，在短时爆发力运动中，3个负荷输出功率分别呈现上升、不变和下降的趋势．
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