The gait cycle is the time interval or sequence of motions occurring between two consecutive initial contacts of the same foot (Figure 14-1). It is synonymous with the stride length. For example, if heel strike is the initial contact, the gait cycle for the right leg is from one heel strike to the next heel strike on the same foot. The gait cycle is a description of what happens in one leg. The same sequence of events is repeated with the other leg, but it is 180° out of phase.⁸ There are spatial descriptors of gait, such as stride length, step length and step width; time or temporal descriptors, such as cadence, stride time and step time; and, descriptors that involve time and space, such as walking speed.¹⁶ Another spatial descriptor that is sometimes discussed with gait is foot angle (Fick angle; see Figure 14-14). Each of these descriptors can and should be very similar for both limbs. For example, osteoarthritis in one hip can change many of the descriptors and the examiner should watch for these changes. Simoneau¹⁷ clearly described the terminology that applies to the gait cycle events (Figure 14-2). Table 14-1 demonstrates the periods or phases of the gait cycle, the function of each phase, and what is happening in the opposite limb.⁸ The gait cycle consists of two phases for each foot: stance phase, which makes up 60% to 65% of the walking cycle, and swing phase, which makes up 35% to 40% of the walking cycle. In addition, there are two periods of double support and one period of single-leg stance during the gait cycle.

As the velocity of the cycle increases, the cycle length or stride length decreases. For example, in jogging, the gait cycle is 70% of the walking cycle, and in running, the gait cycle is 60% that of walking.¹⁸ In addition, as the speed of movement increases, the function of the muscles changes somewhat, and their electromyographic activity may increase or decrease. Generally, gait velocity decreases with age.¹⁹ Montero-Odasso et al.²⁰ found the gait velocity (less than 0.8 m/sec) could be used to determine mobility impairment in the elderly.

The stance phase of gait occurs when the foot is on the ground and bearing weight (Figure 14-3). It allows the lower leg to support the weight of the body and, by so doing, acts as a shock absorber while allowing the body to advance over the supporting limb.¹⁸ Normally, this phase makes up 60% of the gait cycle and consists of five subphases, or instants.

The initial contact instant is the weight-loading or weight acceptance period of the stance leg, which accounts for the first 10% of the gait cycle. During this period, one foot is coming off the floor while the other foot is accepting body weight and absorbing the shock of initial contact. Because both feet are in contact with the floor, it is a period of double support or double-leg stance.

The load response and midstance instants consist of the single support or single-leg stance, which accounts for the next 40% of the gait cycle. During this period, one leg alone carries the body weight while the other leg goes through its swing phase. The stance leg must be able to hold the weight of the body, and the body must be able to balance on the one leg. In addition, lateral hip stability must be exhibited to maintain balance, and the tibia of the stance leg must advance over the stationary foot.

The terminal stance and preswing instants make up the weight-unloading period, which accounts for the next 10% of the gait cycle. During this period, the stance leg is unloading the body weight to the contralateral limb and preparing the leg for the swing phase. As with the first two instants, both feet are in contact, and so double support occurs for the second time during the gait cycle.

The swing phase of gait occurs when the foot is not bearing weight and is moving forward (Figure 14-4). The swing phase allows the toes of the swing leg to clear the floor and allows for leg length adjustments. In addition, it allows the swing leg to advance forward. It makes up approximately 40% of the gait cycle and consists of three subphases.

Acceleration occurs when the foot is lifted off the floor. During normal gait, rapid knee flexion and ankle dorsiflexion occur to allow the swing limb to accelerate forward. In some pathological conditions, loss or alteration of knee flexion and ankle dorsiflexion leads to alterations in gait.

The midswing instant occurs when the swing leg is adjacent to the weight-bearing leg, which is in midstance.

During the final instant (terminal swing or deceleration), the swinging leg slows down in preparation for initial contact with the floor. With normal gait, active quadriceps and hamstring muscle actions are required. The quadriceps muscles control knee extension, and the hamstrings control the amount of hip flexion.

During running or with increased velocity, the stance phase decreases and a float phase or double unsupported phase occurs while the double support phase disappears (Figure 14-5).^18,21 Although the single-leg stance phase decreases, the load increases two or three times.²² The motion occurring at each of the joints (pelvis, hip, knee, ankle) is similar for walking and for running, but the required range of motion (ROM) increases with the speed of the activity. For example, hip flexion in walking is about 40° to 45°, whereas in running it is 60° to 75°.²³

Double-leg stance is that phase of gait in which parts of both feet are on the ground. In normal gait, it occurs twice during the gait cycle and represents about 25% of the cycle. This percentage increases the more slowly one walks; it becomes shorter as walking speed increases (Figure 14-6) and disappears in running.

The normal base width, which is the distance between the two feet, is 5 to 10 cm (2 to 4 inches; Figure 14-7). If the base is wider, the examiner may suspect some pathology (e.g., cerebellar or inner ear problems) that results in poor balance, a condition such as diabetes or peripheral neuropathy that may indicate a loss of sensation, or a musculoskeletal problem (e.g., tight hip abductors). In the first two cases, the patient tends to have a wider base to maintain balance. With increased speed, the base width normally decreases to zero, and in some cases, crossover occurs, in which one foot lands where the other should and vice versa. Such crossover can lead to gait alterations and other problems.²⁷

Step length, or gait length, is the distance between successive contact points on opposite feet (see Figure 14-1). Normally, this distance is about 72 cm (28 inches) being relatively constant for each individual (i.e., step length is commonly related to preferred walking speed)^17,28 and should be equal for both legs. It varies with age and sex with children taking smaller steps than adults and females taking smaller steps than males.²² Height also has an effect: a taller person takes larger steps. Step length tends to decrease with age, fatigue, pain, and disease. If step length is normal for both legs, the rhythm of walking is smooth. If there is pain in one limb, the patient attempts to take weight off that limb as quickly as possible, altering the rhythm.

Stride length is the linear distance in the plane of progression between successive points of foot-to-floor contact of the same foot. The stride length is normally about 144 cm (56 inches) and in reality is one gait cycle.17 Stride length, like step length, decreases with age, pain, disease, and fatigue.^19,29 The age changes are often the result of decreased walking pace or speed.^29,30

Lateral pelvic shift, or pelvic list, is the side-to-side movement of the pelvis during walking. It is necessary to center the weight of the body over the stance leg for balance (Figure 14-8). The lateral pelvic shift is normally 2.5 to 5 cm (1 to 2 inches). It increases if the feet are farther apart. The pelvic list causes relative adduction of the weight-bearing limb, facilitating the action of the hip adductors. If the abductor muscles are weak, a Trendelenburg gait results (see Figure 14-21).

Vertical pelvic shift keeps the center of gravity from moving up and down more than 5 cm (2 inches) during normal gait. By means of a vertical pelvic shift, the high point occurs during midstance and the low point during initial contact; the height of these points may increase during the swing phase if the knee is fused or does not bend because of protective spasm or swelling. The head is never higher during normal gait than it is when the person is standing on both feet. Therefore, if a person can stand in an opening, he or she should be able to move through the opening without hitting the head.7 On the swing phase, the hip is lower on the swing side, and the patient must flex the knee and dorsiflex the foot to clear the toe. This action shortens the extremity length at midstance and decreases the center of gravity rise.

Pelvic rotation is necessary to lessen the angle of the femur with the floor, and, in so doing, it lengthens the femur (Figure 14-9). The rotation decreases the amplitude of displacement along the path traveled by the center of gravity and thereby decreases the center-of-gravity dip. There is a total of 8° pelvic rotation with 4° forward on the swing leg and 4° posteriorly on the stance leg. To maintain balance, the thorax rotates in the opposite direction. When the pelvis rotates clockwise, the thorax rotates counterclockwise, and vice versa. These concurrent rotations provide counter-rotation forces and help regulate the speed of walking.

In the lower limb, rotation is evident at each joint (Figure 14-10). The farther the joint is from the trunk, the greater the amount of rotation. For example, rotation in the tibia is three times greater than rotation in the pelvis.⁷

The normal cadence is between 90 and 120 steps per minute which varies, in part, because of the height of the individual.31–34 The cadence of women is usually six to nine steps per minute higher than that of men.³³ With age, the cadence decreases. Figure 14-11, A, illustrates the cadence of normal gait from heel strike to toe off showing the changing weight distribution. With pathology or deformity (e.g., a cavus foot [Figure 14-11, B]), this weight-bearing pattern may be altered. As the pace of walking increases, the stride width increases, and the toeing-out angle decreases. Gait speed is about 1.4 m/sec (3 mph).¹⁷

As previously mentioned, there are five instants involved during the stance phase of gait. These are now described in order of occurrence. This phase is the closed kinetic chain phase of gait. The action occurring at the various joints causes a chain reaction because of the stresses put on the joints and supporting structures with weight-bearing. The foot becomes the fixed stable segment, and alterations occur from the foot up with the joints of the foot adapting first, followed by those of the ankle, knee, hip, pelvis, spine, and finally the upper limb, which acts as a counterbalance to movement in the lower limb.37 The relations between the joints are constantly changing. Table 14-2 summarizes the movement at the hip, knee, ankle, and foot during the stance phase.³⁸

The swing phase of gait involves the lower limb in an open kinetic chain; the foot is not fixed on the ground, and the stresses on the limb are therefore less and easier to dissipate. During this phase, alterations occur from the spine down through the pelvis, hip, ankle, and foot. The pelvis and hip provide the most stability in the lower limb during the non–weight-bearing phase. Table 14-3 summarizes the motions occurring in the lower limb during the swing phase.

The three instants composing the swing phase of gait are now described in order of occurrence.

Initial Swing

During the first subphase of acceleration (Figure 14-12), flexion and medial rotation of the hip and flexion of the knee occur. The pelvis medially rotates and dips to the swing leg side. The trunk is aligned with the stance leg. In addition, the ankle continues to plantar flex. The foot is not in contact with the floor. The forefoot continues supinating, and the hindfoot continues everting. The dorsiflexor muscles of the ankle contract to allow the foot to clear the ground, and the knee exhibits its maximum flexion during gait of about 60°. If the quadriceps muscles are weak, the trunk muscles thrust the pelvis forward to provide forward momentum to the leg.

Although there is a tendency to talk about gait as action around joints, the examiner must not forget that muscles play a significant role in what happens at the joints. Table 14-4 illustrates the actions of some of the muscles used during gait.⁴⁰