The Gait Cycle-Walking Code Style

The Gait Cycle

The gait cycle describes bipedal human locomotion, following the course of a single leg through a full stride. 

What is a Stride:

A stride is the distance traveled between the initial contact of one foot with the ground and the next time that foot with the ground. In other words, a stride is two full steps. 

What is a step:

A step is the movement between the initial contact with one foot and the initial contact of the next foot. 

Phases of the Gait Cycle

The gait cycle is divided into two primary phases, the Stance Phase and the Swing Phase. During the stance phase, the reference leg is in contact with the ground. During the swing phase, the reference leg is swinging and not in contact with the ground. The stance phase takes up approximately 60 percent of the cycle and the swing phase takes up approximately 40 percent of the cycle. In part of the stance phase, both feet are in contact with the ground. This portion of the stance phase is called double leg stance, or double leg support. When the stance leg is the only leg in contact with the ground, it is called single leg stance, or single leg support.

Loading Response

The first part of the stance phase is the Loading Response phase. Loading Response begins at initial foot contact, generally with the heel, and concludes right before toe off. This all takes place during double leg support.

Loading Response is extremely important because it includes the initial impact of the foot with the ground and the subsequent absorption of all of the force onto the standing leg. This is the portion of a step where the most injury can be done. Proper execution of this phase is essential to preventing injury or the chronic repetitive wear and tear that can lead to a number of painful medical conditions, including plantar fasciitis, flat feet, bunions, hammertoes, knee pain, hip pain, and more. 

Core Movements During Loading Response

During Loading Response, the arm will begin to swing forward on the side of the stance leg. This follows the forward rotation of the upper part of the abdominal core which triggers the lowering of the heel and initial contact at the end of the previous step. As soon as initial contact is made, the lower abdominal muscles on the side of the stance leg should engage, assisting with the transfer of weight. The speed of the change of weight will be proportional to the speed of the lower abdominal muscle engagement. It will also be proportional to the speed of rotation of the upper abdominal muscles, which coordinate with the lower abdominal muscles on the same side of the body. 

The opposite hip will actively flex, pulling forward, during loading response. This helps with the forward shift of the center of gravity. 

Walking Code Core Technique During Loading Response

Core Technique: Set

Hip Action: Flexion of the swing leg hip:
Upper Torso Rotation: Forward on the side of the standing leg
Lower Torso Rotation: Backward on the side of the standing leg

Peripheral Actions

Knee: Flexion on the side of the standing leg
Ankle: Plantarflexion on the side of the standing leg

Midstance

The phase following the Loading Response is the Midstance phase. This begins when the swing leg leaves the ground and ends after the swing leg moves forward and the tibia of the swing leg is perpendicular to the ground. The picture above shows the Midstance Position, which occurs half way between the beginning and end of the midstance phase, when the swing leg ankle reaches the position to the side of the standing leg.

Core Movements

The upper and lower torso, guided by their respective abdominal muscles, continue rotating in the same manner as during the Loading Response. The upper torso continues turning forward on the side of the standing leg. The lower torso continues turning backward on the side of the standing leg. The hip action is what changes to initiate the midstance phase. The active hip flexion changes from the swing leg hip to the standing leg hip. The feeling should be that of trying to lift the standing leg forward, rather than trying to push it back. This is an eccentric contraction of the hip flexors since they will in fact lengthen during the process as a result of the other movements which are taking place during midstance. 

Core Technique During Midstance

Hip Action: Flexion of the standing leg hip
Upper Torso Rotation: Forward on the side of the standing leg
Lower Torso Rotation: Backward on the side of the standing leg.

Peripheral Actions

Knee: Extension of the standing leg knee
Ankle: Dorsiflexion of the standing leg ankle

Terminal Stance

The next stance phase is called terminal stance. This occurs between the end of midstance and when the swing leg heel makes initial contact with the ground. This is not just a phase based on position of the legs. Just like the other phases, terminal stance is performed with a specific action of the core that triggers it. This core action is a change of the rotation of the upper part of the abdominal core from forward on the side of the standing leg to forward on the side of the swing leg. Initiating terminal stance of the right leg, the left upper torso must begin turning forward. That forward movement of the left upper torso, guided by the rotation of the upper abdominal muscles on the left, brings the left heel down to the ground. This movement is what will eventually begin to swing the left arm forward and allow the right arm to begin dropping back. This change in core movement also triggers the reflexive actions of added extension of the standing leg knee and plantarflexion of the standing leg ankle. The ankle plantarflexion will bring the heel of the standing leg up, called Heel Lift, which occurs during Terminal Swing. 

Pre-Swing

The final stance phase of the stride is the pre-swing phase. Pre-swing is the phase that begins after initial heel contact of the opposite leg foot and ends with toe off of the reference leg. This is the Loading Response phase of the opposite leg.

Initial Swing and Midswing

The swing leg begins to swing (initial swing) and continues swinging until the tibia of the swing leg reaches a position perpendicular to the ground. I do not distinguish between these two phases because the core and peripheral actions do not change. The upper torso turns forward on the side of the standing leg and the lower torso turns backward on the side of the standing leg. The hip of the standing leg will be flexing. The reference leg, now the swing leg, will be swinging passively. When I say passively, I mean that you are no longer actively lifting the swing leg hip. The lifting energy will becoming from the standing leg hip during this part of the gait cycle. 

Terminal Swing

The final part of the swing phase is Terminal Swing. This occurs during the Terminal Stance Phase of the opposite leg. The knee of the swing leg will passively extend during terminal swing until the heel contacts the ground. The ankle of the swing leg will be in a passively dorsiflexed position prior to the foot making initial contact.