Running, like walking, is a cyclic activity; one running stride follows another in a continuous pattern. We define a running stride as being from touchdown of one foot to the next touchdown of the same foot, or from toe-off to toe-off. Running can basically be divided into a support phase, when one foot is on the ground, and a recovery phase, in which both feet are off the ground.

The runner can only apply force to the ground for propulsion during the support phase, which defines that phase’s main biomechanical function and provides the key events that indicate the start of the phase, touchdown (or foot strike), and its end, toe-off.

The support phase starts at toe-off and ends at touchdown; at this stage, we will consider its function to be to prepare the leg for the next touchdown. In slow running, or jogging, the recovery phase will be very short; it will then increase with running speed.