Fig. (2) Force-displacement curves for the aACL for Knee #1 at all five zero-load length percentages (75%, 80%, 85%, 90%, and 95%). The non-linear toe region and linear stiffness (k) are pointed out on the 85% curve. This figure shows how changing the zero-load length percentage impacts the non-linear toe region. Note that linear stiffness (k) in this figure has the units N/mm.