Gait cycle

Stance phase

The stance phase is the period of the gait cycle when the foot is on the ground and bearing body weight. More specifically, it can be described as the period between the moment that the heel of the foot touches the ground (heel strike) until the moment that the toe-off occurs.
The stance phase consists of five subphases;

1. The heel strike (initial response, contact response, or weight acceptance). In this subphase, the heel of the foot makes initial contact with the ground. It requires the body’s weight to be accepted by the leg making contact with the ground.
2. The foot flat (loading response) is the second subphase when the foot rolls forward until the entire plantar surface is in contact with the ground.
3. The midstance starts when the weight of the body is propelled forward, directly over the lower extremity, so that the greater trochanter of femur is directly above the middle of the foot. At this stage, our entire body weight is being balanced over one leg.
4. The next substage is heel-off and includes lifting the heel off the ground. This is when we start to shift the body weight onto the contralateral leg.
5. The toe-off is the final stage of the stance phase and includes pushing the toes into the ground while the ankle plantarflexes, creating forward propulsion.

Swing phase

The swing phase is the second phase of gait when the foot is free to move forward. It is described as the period between toe-off and heel strike.
There are three subphases of the swing phase:

1. The early swing (acceleration phase) is the first sub-phase during which the foot is lifted from the ground. The ankle dorsiflexes and the knee flexes so that the foot and toes can be moved from the ground. The hip flexes to bring the leg forward, moving it directly under the body.
2. The mid-swing phase is the second phase when the non-weight-bearing leg passes directly beneath the body and past the weight-bearing leg. At the same time, the trunk is moved forward so that the weight of the body is directly over the weight-bearing leg.
3. The late swing (deceleration phase) is the last subphase. The foot is moved to a position in front of the body, the knee extends and momentum decelerates. The lower limb is now ready for heel strike and prepares to accept the transfer of body weight, for the start of the next stance phase.

As the legs move, so does the rest of the body. The pelvis rotates forward along with the swing leg, while at the same time the thorax and spine rotate in the opposite direction to maintain balance. The contralateral arm assists balance and propulsion, by swinging forward at the same time as the opposite leg.

Hip joint

The hip joint flexes during the swing phase and extends during the stance phase of gait. Hip flexion is created by the hip flexor muscles to produce the forward swing movement of the lower extremity. This action is performed predominantly by the iliopsoas muscle. This movement is facilitated by the eccentric contraction of the hamstring muscles (biceps femoris, semimembranosus, semitendinosus). Hip extensor muscles (gluteus maximus and the hamstring muscles) act to stabilize the pelvis during shock absorption and to control the forward momentum of the body as the weight is shifted forward over the stance leg. Hip abductor muscles, mainly gluteus medius and gluteus minimus act to stabilize the pelvis, preventing pelvic dropping on the side of the free leg. The hip adductor muscles control the balance in the weight-bearing leg.

Knee joint

The knee is held in a stable extended position as the foot makes contact with the ground during heel strike by concentric contraction of the quadriceps muscle group and eccentric contraction of the hamstring muscles. The knee remains (predominantly) extended throughout the stance phase to allow for stable weight-bearing by the lower limb. However, a small “flexion wave” movement is seen within the knee as the lower limb absorbs shock in contact with the ground. The swing phase sees the knee move from extension into flexion, then back to extension. This fluid action is due to the joint action of both the knee flexor muscles and the knee extensor muscles to ensure controlled acceleration and deceleration of the leg.

Foot and ankle

The ankle is dorsiflexed as the foot swings through to make contact with the ground at heel strike. Then immediate plantarflexion occurs, controlled by eccentric contraction of the ankle dorsiflexor muscles (tibialis anterior, extensor digitorum longus, extensor hallucis longus, fibularis tertius), as the foot rolls forward into the foot flat position. Forceful plantarflexion then occurs, by the action of the gastrocnemius and soleus muscles, creating propulsion during heel-off and toe-off stages.