|（Department of Physical Education，Zhengzhou University，Zhengzhou 450001，China)
Abstract: In order to observe the functions of lower limb muscles and the kinematic characteristics of knee joints during underwater knee joint rehabilitation training universally used nowadays, the author selected 20 healthy college students (10 female students and 10 male students) as his research subjects from a physical education institute, recorded the electromy-ographic signals of the quadriceps femoris muscles (vastus medialis muscle, vastus lateralis muscle) and hamstring mus-cles (biceps femoris muscle, semitendinosus muscle) of the testees by using a surface electromyography when the testees were doing one time maximum knee joint flexion and extension and continuously repeated multi-times knee joint flexion and extension respectively, and recorded knee joint movement underwater (at a shooting frequency of 25 Hz) by using con-stant speed cameras. The author revealed the following findings: when knee joints were doing continuously repeated flex-ion and extension, at the initial stage of movement, the myoelectric activity of antagonistic muscles was lower than that of agonistic muscles, later, the activity of antagonistic muscles gradually increased to the maximum; while during one time knee joint flexion and extension, the myoelectric activity of agonistic muscles was activated to the maximum before knee joints moved, and in the entire range of movement, the myoelectric activity of antagonistic muscles was lower than that produced during continuously repeated flexion and extension, but in the late period of movement, the level of myoelectric activity of agonistic muscles produced during one time movement was higher than that produced during repeated move-ment; under the two rehabilitation training modes, the angular speed mode and peak angular speed of knee joints were similar. The said findings indicate the followings: one time underwater flexion and extension is conducive to the exercising of agonistic muscles; when doing continuously repeated multi-times knee joint flexion and extension, the activity of ago-nistic muscles gradually weakens, antagonistic muscles are enhanced; such a training mode is conducive to the rehabilita-tion of patients having an injured anterior cruciate ligament.
Key words: sports biomechanics；knee joint flexion and extension underwater；surface myoelectricity