Hamstring curls are performed with the two different arrangements of external weights as shown. In the first arrangement in the left image, the weight W is split onto the end of two bars rigidly held at a right angle. In the second arrangement, the total weight W is only on the end of one bar. Find expressions for the force in the hamstrings for these two arrangements as a function of knee flexion angle (slight flexion to 90°) and computer plot as a % of W. Describe the effectiveness of exercising the muscle with the 2 arrangements.

Assume that the center of rotation for weights is at the knee joint, the length of each weight's bar is the same as the tibia length, and the direction of hamstring contraction remains constant with knee flexion angle. Neglect limb segment weight.