A number of factors can impact gait. These include footwear, clothing and environmental influences such as slopes or stairs. They can also impact walking speed and the quality of movement.

A model is used to examine the contribution of six gait determinants on vertical center-of-mass trajectory and vertical ground reaction force. The model is divided into three phases:

Stance Phase

In normal walking, each foot contacts the ground for about 20% of the gait cycle. This period is called the double-support phase and can be subdivided into the initial, mid and terminal double-support phases. The other 50% of the gait cycle is spent in single-support. A special case is running, in which there are parts of the gait cycle where neither foot contacts the ground (a float phase).

Stance Phase

The stance phase starts with the first heel contact, i.e., the load response or foot-flat phase. This is followed by the transfer of body weight to the supporting leg and a small “flexion wave” movement at the knee joint. This is accompanied by internal rotation of the tibia-fibula joint and external rotation of the ankle joint, and by supination of the foot.

After a brief duration in the float phase, the leading leg initiates the swing phase by pushing off with the toe. This is followed by the supine foot extension to provide forward propulsion. The swing phase can also be divided into the initial swing, the mid-swing and the terminal swing. Understanding the stance and swing phase of gait can help us to understand some fundamental aspects of human locomotion. It is important for treating gait disorders and designing lower-limb prostheses. Currently, the best way to quantify this is through muscle blood flow measurements. However, these methods are limited in their application and cannot be applied to humans while walking at natural speed.

Foot-Flat Phase

Once the foot becomes flat – the forefoot comes in contact with the running surface – the next phase of the gait cycle commences -propulsion (or toe off). This is also known as the double support phase and makes up 14-20% of the stance phase. If excessive foot pronation continues during the initial and terminal double support phases this can cause instability of the foot and leg leading to increased injury risk.

During this period the weight of the body is transferred from the heel to the foot, the soft tissues tighten and the arch of the foot rises. This process is controlled by the windlass mechanism which is a group of muscles (tibialis anterior, extensor hallucis longus, fibularis tertius and the plantar fascia) extending from the heel to the base of the first metatarsal bone (first proximal phalanx).

This is a complex mechanical process that is difficult to quantify. The foot and leg can be influenced by many different factors such as footwear, terrain, floor, working conditions etc. However, it is possible to use a 3D foot scanning system to capture spatial/temporal information and measure the force applied to the foot during a normal walking cycle. By analysing the distribution of vertical ground reaction force (VGRF) and the rate of change in footprint area during the foot-flat phase it is possible to determine whether a person has a low or high arched foot.

Mid-Swing Phase

Gait is a complex action that requires the coordinated movement of multiple joints and muscles in our lower limbs, feet, hips and pelvis. The gait cycle can be divided into two phases: stance and swing. During the stance phase, the foot is on the ground while during the swing phase the foot is off the ground. The stance phase can further be subdivided into several parts including initial contact, foot flat and loading response. The swing phase is subdivided into pre-swing, mid-swing and terminal swing.

The stance phase is a weight-bearing activity, which is performed predominantly by the quadriceps muscle group and some of the hamstring muscles. The knee remains (predominantly) extended during this phase to allow stable weight-bearing and shock absorption. The knee is also flexed during the mid-swing phase to allow movement of the swing leg forward and preparing for the next step.

The first portion of the swing phase is called the initial swing, which accounts for 10-15% of the gait cycle. During the initial swing, the reference leg leaves the ground and lifts off with its toes. This motion is assisted by the initial contact phase, during which the knee flexes and ankle dorsiflexes to help stabilize the foot. The initial swing also includes a small flexion wave at the knee to absorb shock as it passes directly under the body.

Terminal Swing Phase

This is the last phase of a step, and it’s a coordinated ballet that sees crucial anatomical players like the hamstrings and the Gluteus Maximus harmonize to regulate the leg’s speed and trajectory for an optimal foot landing. Discord in this phase could trigger a host of problems, such as irregular landing mechanics and compensatory movements that shorten stride length or lead to running efficiency compromises.

Throughout a normal walk, both legs are in contact with the ground for 20% of the gait cycle—from initial contact to contralateral toe off. This is known as double support, and it is only interrupted by a brief period of float in which neither foot makes contact with the ground.

In this study, we investigated how the force-generating muscle actions of the stance and swing limbs varied with walking speed. We found that muscles on the stance limb powerfully accelerated knee extension on the subject’s faster speeds, while velocity-related forces slowed the stance-limb knee’s motion on their slowest speeds (Fig. 6A, dark grey bars).

The first sub-phase of a double-support cycle is the loading response, which spans from heel contact to the first point where the leg lifts off the ground (toe-off). This phase absorbs shock and helps the stance limb transfer body weight from one foot to another. The next phase is mid-stance, which lasts from the toe-off of the contralateral leg to when the lead leg’s heel comes off the ground (the point at which the leading leg enters terminal stance). It accounts for 29-37% of the stance phase. The final phase is the terminal swing phase, which takes up 15-22% of the total double-support cycle.