A 72 kg individual is in a seated position on a machine that tests knee extension strength. The calf length is 0.400 m, calf/foot mass is 5.8% of the body mass, calf/foot center of mass is 53% of the calf length from the knee joint, and calf/foot moment of inertia about the knee joint is 0.311 kgm2. The quadriceps moment arm is 0.040 m. The machine's padding contacts the calf at a constant moment arm (does not change with knee angle) of 0.378 m from the knee joint.

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

A. 22 N

B. 41 N

C. 52 N

D. 217 N 

2.) Still at zero machine resistance, the knee joint angle is held at a constant 50ï° below the horizontal (knee flexion). How much quadriceps muscle force is being generated?

A. 14 N

B. 140 N

C. 166 N

D. 217 N 

3.) After setting the machine resistance to 210 N, the knee joint angle is held at a constant 50ï° below the horizontal. How much quadriceps muscle force is being generated?

A. 1985 N

B. 1999 N

C. 2124N

D. 2202 N 

4.) With a machine resistance of 210 N, the knee joint angle is 50ï° below the horizontal and has

an angular acceleration of 15 rad/s2. How much quadriceps muscle force is being generated?

A. 2007 N

B. 2115 N

C. 2241 N

D. 2318 N 

5.) What type of muscle contraction is occurring as the knee is extending in part 4.)?

A. concentric hamstrings

B. isometrichamstrings

C. concentricquadriceps

D. eccentric quadriceps