Question

A 82 kg individual is in a seated positio n on a machine that tests knee extension strength . The calf length is 0.44 m , the c alf/foot mass is 5.9 % of the body mass, t he calf/foot center of mass is 59 % of the calf length from the knee join t, and t he calf/foot mo ment of iner tia about the knee joint is 0.36 kgm 2 . The quadriceps moment arm is 0.04 3 m. T he machine’s padding co ntacts the calf at a constant moment arm of 0.41 m from the knee joint .   

a) At zero machine resistance, the knee joint angle is held at a constant 0 ? (full extension) with the calf in a horizontal position . H ow much quadriceps muscle force is being generated?

A. 16 N

B. 62 N

C. 287 N

D. 666 N

b) S till at zero machine resistance , the knee joint angle is held at a constant 55 ? below the horizontal (knee flexion). How much quadriceps muscle force is being generated?

A. 1 7 N

B. 164 N

C. 235 N

D. 561 N

c) After setting the machine resistance t o 185 N, the knee join t angle is held at a constant 55 ? below the horizontal. How much quadriceps muscle force is being generated?

A. 1496 N

B. 1529 N

C. 1928 N

D. 2957 N

d) With a machine resistance of 185 N, the knee joint angle is 55 ? below the horizontal and is extending with an angular acceleration of 14 rad/s 2 . How much quadriceps muscle force is being generated?

A. 2046 N

B. 2586 N

C. 3297 N

D. 4608 N

e) What type of muscle contraction is occurring as the knee is extending in part d)?

A. Concentri c Hamstrings

B. Concentric Quadriceps

C. Eccentric Quadriceps

D. Isometric   

Answer 1