The lumbar portion of the human spine supports the entire weight of the upper torso and the force load imposed on it. We consider here the disk (shaded red) between the lowest vertebra of the lumbar region (L5) and the uppermost vertebra of the sacrum re-gion.
(a) For the case L = 0, determine the compressive force C and the shear force S supported by this disk in terms of the body weight W. The weight Wu of the upper torso (above the disk in question) is 68% of the total body weight W and acts at G1. The vertical force F which the rectus muscles of the back exert on the upper torso acts as shown in the figure.
(b) Repeat for the case when the person holds a weight of magnitude L = W/3 as shown. State any assumptions.
