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BACKGROUND: In lower steps, downhill running, and squatting training, the lower limb muscles are in centrifugal contraction, and it is easy to cause soreness of extensor muscles and minor muscle damage. However, there are few reports on the injury caused by the application of elbow flexor with the same centrifugal speed to extensor muscles. OBJECTIVE: To reveal the law of muscle injury by given maximum isokinetic eccentric contraction exercise at fast and slow speeds to the knee extensor. METHODS: The study was approved by the Ethics Committee of Chongqing Vocational College of Applied Technology. Sixteen untrained healthy male college students were selected and signed the informed consents. During the period of 2 weeks, the left and right legs of each participant were given 120 seconds of maximum isokinetic eccentric contraction exercise at slow ((30 (°)/s, 6 groups x 5 times)) and fast (210 (°)/s, 6 groups x 35 times) speeds, respectively. The degree of muscle soreness, thigh circumference, knee joint range of motion, maximum autonomic isometric muscle strength, and blood creatine kinase activity were measured before and after exercise. RESULTS AND CONCLUSION: (1) Muscle soreness peaked at 2-3 days after the end of training at different speeds, which showed that muscle soreness induced by rapid training was more serious than slow training, but both of them could recover to the level before training on day 5 after the end of exercise. (2) Thigh circumference increased at different speeds, but thigh circumference increased significantly faster than slow training and recovered more slowly. (3) The range of motion and maximum isometric muscle strength of knee joint after rapid training were significantly lower than those after slow training. The recovery speed of both was significantly different, which showed that range of motion of knee joint and maximum isometric muscle strength decreased slowly after slow training, and basically returned to the level after training on day 3 after the end of slow training. In fast condition, range of motion of knee joint and maximum isometric muscle strength decreased significantly, peaked later, and recovery was more significant, and took longer time to recover completely on day 5 after the training. (4) The creatine kinase activity induced by fast training was significantly higher than that induced by slow training, and the slow training could recover quickly, but the creatine kinase activity of fast training group was still increasing on day 5 after the end of training, which showed that the muscle damage caused by fast training was much higher than that caused by slow training. (5) These results imply that the difference of muscle soreness, thigh circumference, range of motion of knee joint, maximum isometric muscle strength, blood creatine kinase, maximal muscle strength and recovery time caused by centrifugal contraction may be related to the total amount of centrifugal training. On the premise of controlling the activation time of fast and slow speed muscles, the degree of muscle injury caused by rapid isokinetic centrifugal training is much higher than that caused by slow speed, which supports the conclusion that centrifugal contraction speed is related to muscle injury. It also confirms that rapid centrifugal exercise is more likely to cause muscle injury. [ABSTRACT FROM AUTHOR]