Practitioners prescribe foot orthotics to improve foot function and relieve pain. This also produces observable changes in other areas of the lower extremities.
The most obvious and well known changes are the reductions in the angle and base of gait. The reduction on the angle of gait with the orthotic plates is generally attributed to the reduction of the adduction of the forefoot on the rearfoot. In reality, it is due to reduction of the adduction of the rearfoot on the forefoot. In short, with a pronated foot, the increase in the angle of gait is due to the medial displacement of the rearfoot. The base of gait is the distance from the medial side of one heel to the medial side of the other heel in relation to the plane of progression. The base of gait reduces with orthotics. This reduction in the base of gait is due to increased stability of the lower extremities. More instability means an increase in the base of gait and vice versa.
Less well-known observable variations in gait revolve around the stride length and velocity. With orthotics, the stride length increases, as does the velocity of the gait while cadence (the number of steps per minute) remains constant. Longer stride length with the same cadence means increased velocity.
But why do these changes occur?
In order to flex and extend at the hip, the leg must internally and externally rotate. Taking this action to the next level, the subtalar joint must pronate and resupinate (with the transversely rotating leg). A maximally pronated subtalar joint impedes transverse plan rotation of the limb, which in turn reduces the hip’s ability to flex and extend. Improving the function of the subtalar joint enables more internal and external rotation of the thigh, which in turn facilitates an increase in the flexion and extension of the hip. The nest result is a longer stride and faster gait.
Observing the rise and fall of the pelvis is perhaps the most interesting aspect of gait changes with and without orthotics. The hip rises at heel contact and falls at heel off. Without orthotics the hip rises dramatically at heel contact (shock?) and falls accordingly at heel off. With orthotics, the hip rise at the moment of heel contact is much less, and correspondingly the hip fall is less at heel off. Ultimately, the decreased vertical oscillations must translate into a more efficient gait simply because the body is putting less energy into the system to raise the weight of the body and less restraint to decelerate the falling hip. The net effect is a more fluid and efficient gait with decreased vertical oscillations at the hip.