BIOM 212: The Gait Cycle - Stance Phases

Initial Contact

• Initial contact is also known as heel strike.
• There is a change in force vector direction immediately after initial contact, from upward to up and back.
• The trunk is twisted, with the left shoulder and the right side of the pelvis at their furthest forwards, and the left arm at its most advanced.
• The hip is around 30 degrees of flexion, which changes little until initial contact, when the gluteus maximus starts to contract, beginning the extension of the hip.
• The knee extends rapidly at the end of the swing phase, becoming nearly fully extended before initial contact.
• The ankle is generally close to its neutral position in plantarflexion/dorsiflexion at the time of initial contact, and the foot is slightly supinated.

Events and Moments

• At the time of initial contact, there is an internal extensor moment at the hip produced by the hip extensors, which generate power as the hip joint moves in the direction of extension.
• The knee shows an internal flexor moment, due to contraction of the hamstrings as they prevent hyperextension at the end of the swing phase.

Mid-Stance

• The trunk begins to gain height and lose forward speed.
• The hip flexion angle is around 25 degrees.
• The knee continues to flex, reaching peak stance phase flexion early in mid-stance, then starts to extend through concentric contraction of the quadriceps.
• The ankle motion changes from plantarflexion to dorsiflexion as the tibia moves over the stationary foot.
• Peak foot pronation and internal tibial rotation occur during mid-stance.

Loading Response

• The ground reaction force direction is upwards and backwards.
• The trunk is at its lowest position during loading response.
• The arms begin to return to their maximum forward and backward positions.
• The hip begins to extend through concentric contraction of the hip extensors, and the knee begins to flex, initiating the stance phase flexion.
• Plantarflexion occurs at the ankle, controlled by eccentric contraction of the tibialis anterior muscle.
• Pronation of the foot and internal rotation of the tibia occur simultaneously.
• The hip shows internal extensor and the knee internal flexor moments with power generation during the loading response phase.