Normal walking and running have a certain degree of vertical oscillation, but we do not want too much, we want the body to move along mostly horizontal path but we do need some dampening of impact loads. We do not want to waste too much energy bouncing up and down. This is mitigated quite a bit by hip and knee flexion, the knee is well positioned to do this the easiest in many cases. Pronation and ankle dorsiflexion do dampen loads as well.
Ivo and I just recorded a class on leg length discrepancies. Here are some factors to keep in mind if there is even the smallest leg length discrepancy, anatomic or functional.
-the short leg may hyperextend at the knee , externally rotate at the hip, as well as supinate the foot (this supination is relative ankle plantarflexion, which can set up increased protective tone in calf complex and reduced strength and exposure to anterior compartment).
-the long leg side may knee flex , internally rotate at the hip, and as well as pronate at the foot (this is relative ankle Dorsiflexion)
Both of these scenarios can be going on at the same time on either leg, or it can be only on one leg. We are not perfectly symmetrical organisms, so these things can set up to help us run and walk more effortlessly, to compensate to get the head and neck properly positioned (normalizing the visual and vestibular centers on the horizon) for balance and movement through the 3 cardinal planes, and to compensate around challenging anatomy or biomechanics.
This is a complex machine, with infinite abilities to compensate and cope. But what we see is the compensation, not the problem. The joint range losses in one joint, the excesses in another, the weakness in one area, the over protection in another, the failure to tolerate loads in another, are all ways of coping and keeping us moving, . . . . . . but sometimes at a cost. . . . . pain.
shawn and ivo, the gait guys