HARP

Looking at our anatomic wheels in the lab, the spokes (long bones) are whatever they are. That leaves pendulum and velocity properties. We can shorten the overall leg length by hyper-flexing the knee and pointing the foot, as speed runners do, for faster thigh forward flexion. Our main variable is speed. It costs energy equally to go faster or to go slower than pendulum properties. Speed in a chosen direction gives us velocity – a vector with magnitude and a relationship to the ground as well as to the person. Slow has more time to oxygenate so has less fatigue despite equal inefficiency. If we consider the whole leg, then, the big contribution is knee motion (flexion/extension) as pivoted on the hip center. Leg = H-K-A which typically is tracked as an angle.