CHAPTER 14 The Kinesiology of Gait


Stride length = 144 cm Spatial Descriptors of Gait


Right heel contact


Left step length = 72 cm Foot angle = 5°–7°


Left heel strike Right step length = 72 cm Right heel contact Step width = 8–10 cm Figure 14.4 Spatial measurements for stride length, step length, step width, and foot angle for a right gait cycle.


contact point of the fi rst heel and the contact point of the second heel (Fig. 14.4). For example, when the right heel contacts the ground, the length between that contact point and the point when the left heel makes contact is the left step length. It is the length the left limb was able to step once the right heel was planted. Step lengths vary depending on the height of the person but typically average 72 cm. The symmetry of the gait cycle can be measured by comparing the right and left step lengths (Fig. 14.4).


A stride is defi ned as the right and left step combined


together. The stride length is measured from the point of contact of one foot to the subsequent point of contact for the same foot and consists of a right step length and a left step length. Stride lengths average about 144 cm, and stride length represents one complete gait cycle (see Fig. 14.4).


Step width is the lateral measurement between the centers of the heels of two consecutive heel strikes. This lateral distance between feet averages 8 to 10 cm. Larger step widths can indicate that the person needs a greater base of support when walking because of decreased stabil- ity and impaired balance. Foot angle, described as the amount of “toe out,” is the angle between the progression of the body during walking and the long axis of the foot. The average adult foot angle is 5° to 7° (see Fig. 14.4).


TEMPORAL DESCRIPTORS OF GAIT


In addition to spatial distances, elements of the gait cycle are measured by time, specifi cally, duration. The time to complete one right or left step is called step time. Cadence, also called step rate, is the number of steps taken per minute. Stride time is the time it takes for a person to complete one full gait cycle. Typically, a healthy adult takes an average of 110 steps per minute. A com- bination of both spatial and temporal measurements is taken when measuring walking speed or gait speed, the distance covered walking during a given amount of time. The speed is measured in either miles per hour or meters per second and is defi ned as the step rate multiplied by the step length. Gait speed varies among individuals and is infl uenced by fi tness levels, strength, balance, age, height, and weight. Studies have validated the associa- tion between decreased ability to walk at normal walking speeds, especially with indoor dwellers, and an increased


risk of falls. Gait speed is used in clinical settings to determine a patient’s risk of falling.


CENTER OF MASS DISPLACEMENT DURING GAIT


The body’s center of mass (COM) is located anterior to the second sacral vertebra. As the body leans forward during walking, the COM of the body is displaced in a linear direction in front of the supporting limbs. The foot steps forward to prevent a loss of balance when the COM moves beyond the body’s base of support of the feet. This repeated forward displacement of the COM and the forward placement of the foot to prevent a fall produce the activity of walking. The COM moves twice in a verti- cal direction, fi rst up and then down, during one com- plete gait cycle. The COM vertical height is at its lowest point during the midpoint of both periods of double limb support. The body lowers as the hip and knee fl ex, acting as shock absorbers during weight-bearing. The COM rises to its maximum height during the midpoint of both periods of single leg support (Fig. 14.5A). As the hip and knee extend to a neutral position, the height promotes clearance of the swing limb. On average, the total amount of vertical displacement of the COM, from lowest to highest point, is about 5 cm for a man. Displacement of the COM during walking is often measured by tracking the movement of the head.


In addition to vertical displacement, the COM moves


laterally, from side to side, during walking. Maximum lateral displacement of the COM occurs to the right at the midpoint of the stance phase on the right leg. Similarly, left maximal lateral displacement occurs at the midpoint of left stance phase. On average, total lateral displacement for an adult is about 4 cm. The amount of lateral displacement increases as the base of support of the feet increases and decreases as the base of support narrows (Fig. 14.5B).


JOINT KINEMATICS DURING GAIT


The activity of walking is produced by the linear progres- sion of the body’s COM, while the joints of the lower


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