Abstract: Three-dimensional analytical system is used to test the parameters of each joint of the supporting and attacking legs from the perspective of biomechanics. According to the "whip-leg "technique of Sanda, 9 value points are identified based on the end points of the five links and middle points of the whip-leg technique. Data analysis is adopted to dissect the second force exertion of the waist. Research results show that: 1) the supporting knee joints T3 to T3-4 are bigger than T3-4 to T4. The hip angle of T3 to T3 is smaller than T3-4 to T4; 2)The knee and hip joint T3-4 of the attacking leg is smaller than T3-4 to T4 while the hip axis and shoulder axis angle increase. These phenomena prove that just before the whip the trunk twists for a second time, i.e. the waist witnesses the second exertion of force.

Key words: sanda, whip-kick, second exertion, sports biomechanics