A forensic analyst is reviewing surveillance footage. The subject walks past the camera in under three seconds. No face. No badge. But the analyst pauses the clip at a specific frame — the instant the heel touches down — and says: that's enough. That single moment, heel striking ground, is the starting gun for an entire biological clock. The timing of the gait cycle is anchored to that point. That is not an arbitrary choice. A gait cycle is formally defined as the interval from one initial-contact event of a foot to the next occurrence of that same event by the same foot. One heel strike to the next heel strike. That interval contains everything. The automated rhythm of walking, driven by subconscious processes, makes gait highly individual and difficult to replicate. Here, the key idea is the internal structure of that rhythm. The gait cycle divides into two primary phases: stance and swing. During stance, the reference foot contacts the ground. During swing, it lifts and advances forward. In typical level walking, stance occupies roughly sixty percent of the cycle. Swing takes the remaining forty. Within those two phases, researchers identify eight distinct sub-events. Think of them as checkpoints on a racetrack — each one a biometric timestamp. Stance opens with initial contact, then loading response, where the limb accepts the body's weight. Midstance follows, as the center of mass progresses over the supporting foot. Terminal stance begins when the heel rises. Preswing is the late-stance handoff, ending at toe-off — the moment the foot leaves the ground and swing begins. Swing then runs through initial swing, midswing, and terminal swing, which decelerates the leg and positions the foot for the next contact. Eight checkpoints. Each one measurable. Each one personal. Here is where it gets interesting for you, Jordan. A complete walking cycle contains two periods of double-limb support — both feet on the ground simultaneously — and two periods of single-limb support. Stance begins and ends with double support. Single support sits between them. As walking speed decreases, double-support time increases, both in absolute duration and as a percentage of the cycle. That relationship is a biometric goldmine. A cautious elderly walker, a person compensating for knee pain, or someone carrying an unfamiliar load — all of them show measurable shifts in double-support percentage. The body's confidence, or lack of it, is written directly into that number. Counterintuitively, the transitions between phases — heel strike and toe-off — may identify a person more reliably than the most visually obvious parts of a stride. Local dynamic stability changes within a single stride, with notable shifts concentrated around exactly those two events. The system is most mechanically vulnerable at those moments. And vulnerability reveals habit. The ankle plantar flexors produce substantial positive power during late stance and push-off, contributing both to accelerating the center of mass and to launching the leg into swing. The precise timing and magnitude of that push-off burst is deeply individual. One more detail worth holding onto. A published analysis found that the ratio between total cycle duration and stance duration averages approximately 1.620 — strikingly close to the mathematical golden ratio. That is not a design choice. It is an emergent property of human biomechanics. The body, optimizing for efficient locomotion over millions of years, landed on a proportion that mathematicians have studied for centuries. The gait cycle is not a smooth, undifferentiated loop. It is a sequence of eight precisely timed checkpoints, each carrying biometric information. The sixty-forty split between stance and swing is the baseline. Double-support time shifts with speed, load, and confidence. The transitions at heel strike and toe-off are the most dynamically unstable — and therefore the most revealing. The takeaway is this: the gait cycle is divided into stance and swing phases, each containing critical biometric checkpoints. Machines that read those checkpoints are not watching you walk. They are reading your biological clock, one heel strike at a time.