Relative sensitivity of effective stress to individual quadriceps muscle forces in the (A) femur and (B) patella cartilage. The sensitivity values represent the projections of a unit vector to a most probable point in a standard normal variate space (Haldar and Mahadevan, 2000). The sensitivity values were averaged over all subjects (n = 37). VML – vastus medialis longus, VMO – vastus medialis oblique, VLL – vastus lateralis longus, VLO – vastus lateralis oblique, VI – vastus intermedius, RF – rectus femoris.