Figure 9 shows an athlete lying on his back, with his right thigh supported by a

ID: 2005967 • Letter: F

Question

Figure 9 shows an athlete lying on his back, with his right thigh supported by a small

stability ball and his right knee slightly bent in a static position. In this position, the

athlete’s quadriceps muscle force supports the shank and foot (lower leg) at an angle =

20° relative to the horizontal. The athlete’s lower leg has a mass of 9 kg, and its c.m. is

located at a distance d = 0.198 m from the knee joint center (see Figure 10). Assume that

the quadriceps tendon is attached to the patella at a distance c = 0.049 m from the knee

joint center, and that its line of pull forms an angle = 26° with the longitudinal axis of

the shank.

What is the magnitude of the force that the quadriceps must exert to keep the leg in this position?

372.7

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