Gait Analysis

Phases of Gait

The gait cycle is divided into two phases, stance and swing ( Fig. 5.1 ). Stance phase is defined as the time during which the limb is in contact with the ground and supporting the weight of the body. Conversely, swing phase is the time when the limb is advancing forward off the ground. During swing phase, the advancing limb is not in contact with the ground and body weight is supported by the contralateral limb. Stance phase occupies 60% of the gait cycle and swing phase occupies 40%. Both phases can be subdivided further.

Temporal (Cadence) Parameters

Distance and time measurements calculated during gait analysis are referred to as cadence parameters ( Box 5.1 ). Step length is defined as the distance between the two feet during double-limb support and is measured from the heel of one foot to the heel of the contralateral foot. Step length can differ between the right and left sides. Stride length is the distance one limb travels during the stance and swing phases. It is measured from the point of foot contact at the beginning of stance phase to the point of contact by the same foot at the end of swing phase. Step time is the amount of time used to complete one step length. Cadence is the number of steps taken per minute. Walking velocity is the distance traveled per time (usually measured in meters per second). Normal values matched for age are available for these cadence parameters.

Box 5.1

Cadence Parameters

• Step length: Distance between 2 feet during double-limb support

• Stride length: Distance one limb travels during stance and swing phases

• Step time: Time needed to complete one step length

• Cadence: Number of steps per minute

• Walking velocity: Distance traveled per time (m/sec)

Small children walk with greater cadence but smaller step and stride lengths, resulting in many quick, small steps. As children grow, their step and stride lengths increase and cadence decreases. ^{, ,} Step length increases linearly with increasing leg length. Nomograms have been constructed to determine normal cadence parameters for children based on their height. Normal children have the ability to vary their walking speed; the ability to increase speed may be impaired in children with neurologic differences such as cerebral palsy.

Neurologic Control of Gait

The entire neurologic system plays a role in gait. Most of the muscular actions that occur during gait are programmed as involuntary reflex arcs involving all areas of the brain and spinal cord. The extrapyramidal tracts are responsible for most complex, unconscious pathways. Miller and Scott proposed the concept of the “spinal locomotor generator,” designated neurons within the spinal cord that are responsible for reflex stepping movements. Golgi tendon units, muscle spindles, and joint receptors produce neurologic feedback and serve as dampening devices for the coordination of gait. Voluntary modulation of gait (e.g., altering speed, stepping over an obstacle, changing direction) is made possible through interaction of the motor cortex. The cerebellum is important in controlling balance.

A child’s gait changes as the neurologic system matures. Infants normally walk with greater hip and knee flexion, flexed arms, and a wider base of gait than older children. As the neurologic system continues to develop in a cephalocaudal direction, the efficiency and smoothness of gait increase. However, when the neurologic system is abnormal (e.g., in cerebral palsy), the delicate control of gait is disturbed, leading to pathologic reflexes and abnormal movements.

Function of Gait

The simplest function of gait is to travel from one point to another. Normal ambulation is likened to a controlled forward fall. The swing limb comes forward to stop the fall and accept the weight of the body. The joint motions inherent in normal gait serve this purpose. Body weight is transferred from one limb to the other in a smooth fashion, and the forward momentum of the body is sustained.