The phase of support quickly the transitions to the phase of impulsion. The leg extends unit in the knot of the knee and the hip, so that the toe stays in contact with the ground like the footpaths that the leg behind the body. The foot pushes backwards and downwards, creating a vector of force in diagonal, that, in a style of efficient operation, is directed directly in center of the runner of the mass. Since the vector diagonal has a vertical component, the phase of unit continues providing a support against the gravity and can be considered like an prolongation of the phase of support. During the passage, the foot can also extend, by a flexion of the soleus muscle and gastrocnemius in calf. In some styles to run, specially to long distance “it shuffles”, that to maintain the feet near the ground, the ankle stays more or less rigid during the inlay. Because the knee is straightened, although not absolutely, great part of the power of the unit comes from the muscular group of the quadriceps, and in some styles to run, the additional energy comes from the bull calves that extend on the foot of a longer trip. This movement is exposed in speed races.

Much has been discussed on the exact nature of the phase of impulsion, since now which has been demonstrated scientifically that the quadriceps does not have activity after the phase of support, is known like the extension paradox in the management. Essentially, the body extinguishes the quadriceps automatically after the weight of the body moves forwards of its foot of support. This has taken to the hypothesis that there is conduction of phase in no execution, and that the weight of the own runner body provides the propulsion during this time, in essence to fall through a created gravitational pair as the general centers of mass of the runner are in a front position of the support foot.