SACH-SAWCH

The knee flexion at heel strike is without any flexor help. The knee extensors tighten to slow the inertial driven knee flexion. This knee flexion is eccentric to the knee extensors which lengthen despite their activation.

Knee flexors are getting a free ride.

Inman found that at midstance the supple ankle freezes solid. The normal ankle joint is not mobile at the key moment of its function. The calf muscles while they are elongating, slow then freeze forward shin motion. The forward inertia of the body keeps on coming as the weight

centered on the heel shifts to midfoot then to forefoot rollover. Keeping stiff at the ankle causes the heel to rise as that body keeps on coming. The heel rise pushes up on the forward body path (90 deg = tangential nudge from below) which keeps the trajectory above from dipping down. What did the heel do? Cushioned the landing. SACH – there it is. Cushion Heel, CH Inertia extends the swinging lower leg (no knee extensors here). The hip extensor/knee flexor hamstrings elongate as they tense to slow the extension of the knee &flexion of the hip. That thigh/foot/shin deceleration kinetic energy gets transferred by the hamstring transmitting that tug to the pelvis. So the hamstring is using hip extension during flexion and also using knee