Phases of Walking Gait

In this slow-motion video of a young woman walking (uploaded by Daniel Leary at    • Biomechanics Ideal Walking Video  ), the phases of walking gait can be clearly seen. "Stance phase" is the phase of walking gait when the foot in on the ground while "swing phase" is the phase of walking gait when the foot is off the ground.

Stance phase begins when the heel first contacts the ground at "heel contact" which is also the beginning of the "contact phase" of walking. Contact phase then ends as the forefoot becomes fully loaded by ground reaction force (GRF) at "forefoot loading".

Forefoot loading also marks the beginning of the "midstance phase" of walking gait at the center of mass (CoM) of the body passes from posterior to anterior to the planted foot. Midstance phase then ends at "heel off" which occurs the instant the heel lifts from the ground.

"Propulsive phase" then begins at heel off and ends at "toe off". Toe off occurs at the instant the toes lift away from the ground. Therefore, the beginning of the stance phase of walking is heel contact, with the end of stance phase being toe off. Swing phase begins at toe off and ends at heel contact.

Note that during walking, the CoM rises in early stance phase to reach its maximum height above the ground at the middle of midstance, when the CoM is directly over the planted foot. The CoM then falls forward from the middle of midstance to reach its lowest level relative to the ground at the instant of heel off of the stance phase foot and heel contact of the contralateral foot. The raising and lowering of the CoM relative to the ground during walking gait is directly opposite to the raising ad lowering of the CoM during running gait.

In walking gait, the CoM is at its highest level relative to the ground at the middle of midstance when the CoM is directly over the foot while, during running, the CoM is at its lowest level when the CoM is directly over the foot. Therefore, the kinetic and potential energy exchanges of walking and running gait in the bipedal human are exact opposites of each other.

Walking is often modeled as an "inverted pendulum" due to the cyclical swinging of the CoM over the planted foot with each walking step. The rising CoM stores potential energy during the first half of stance phase due to the increased height of the CoM relative to the ground. Then, after the middle of midstance of walking, the CoM falls downward, gaining kinetic energy during the last half of stance phase to the gradually accelerating CoM which reaches its lowest level of potential energy at heel off. In this way, metabolic energy is conserved during walking by this cyclical movement of the CoM over the planted foot with each walking step, using as an inverted pendulum as the energetic model.