Human walking is a controlled fall, repeated over and over. Each step is part of a predictable, cyclical pattern called the gait cycle. A single gait cycle is defined as the time from when one foot makes initial contact with the ground until that same foot makes contact again. It’s one full stride.

This cycle is split into two main parts. The stance phase is when the foot is on the ground, bearing weight. It makes up about 60% of the cycle. The swing phase is when that same foot is in the air, advancing forward. This accounts for the remaining 40%.

To analyze movement more precisely, clinicians and researchers break these two phases down further. The most widely used system is the Rancho Los Amigos nomenclature, which divides the gait cycle into eight distinct functional events. This level of detail helps pinpoint exactly where in the cycle an inefficiency or impairment might be occurring.

Let's walk through the stance phase first. It begins with Initial Contact, usually when the heel strikes the ground. This is immediately followed by the Loading Response, a critical period of shock absorption and weight acceptance. During this time, both feet are on the ground briefly. This is the first period of double-limb support.

Next comes Mid-Stance, where the body's center of mass passes directly over the supporting foot. This is a period of single-limb support, where the opposite leg is in its swing phase. It requires significant stability. Terminal Stance follows, as the heel of the supporting foot begins to lift off the ground, and the body continues to move forward past the foot. The stance phase concludes with Pre-Swing. This is the second and final period of double-limb support, as the other foot makes its own initial contact. The toes of the original foot push off the ground, preparing to leave it.

Now the leg is airborne. The swing phase begins with Initial Swing, where the foot is lifted off the floor and the knee flexes to allow for foot clearance as the leg swings forward. Without adequate clearance, the toe would drag.

During Mid-Swing, the swinging limb is directly opposite the stance limb, like two pendulums passing each other. The final phase is Terminal Swing, where the knee extends in preparation for the next initial contact, and the leg slows down to ensure a controlled and stable landing. This completes the cycle, readying the limb to begin stance all over again.

Beyond the phases, we also measure walking using temporal and distance parameters. A stride is one full gait cycle. A step is the distance from the initial contact of one foot to the initial contact of the opposite foot. In a typical gait, two steps (one left, one right) make up a full stride.

Cadence, or step rate, is the number of steps taken per minute. Together, these parameters create a snapshot of a person's walking efficiency, stability, and speed.

Understanding these phases and parameters is the first step in analyzing human movement. It provides a framework for identifying which parts of this intricate cycle might be contributing to pain or inefficiency.