Biomechanics of the Gait : 2 : Biomechanics of the Gait : 2 Dr. Dibyendunarayan Bid [PT] The Sarvajanik College of Physiotherapy, Rampura, Surat
Gait Terminology: Gait Terminology Time and distance are two basic parameters of motion, and measurements of these variables provide a basic description of gait. Temporal variables include stance time, single-limb and double-support time, swing time, stride and step time, cadence, and speed. 7/2/2012 dnbid71@gmail.com 2
PowerPoint Presentation: The distance variables include stride length, step length and width, and degree of toe-out. These variables, derived in classic research of over 30 years ago, provide essential quantitative information about a person’s gait and should be included in any gait description. 7/2/2012 dnbid71@gmail.com 3
PowerPoint Presentation: Each variable may be affected by such factors as age, sex, height, size and shape of bony components, distribution of mass in body segments, joint mobility, muscle strength, type of clothing and footgear, habit, and psychological status. 7/2/2012 dnbid71@gmail.com 4
PowerPoint Presentation: Stance time is the amount of time that elapses during the stance phase of one extremity in a gait cycle. Single-support time is the amount of time that elapses during the period when only one extremity is on the supporting surface in a gait cycle. 7/2/2012 dnbid71@gmail.com 5
PowerPoint Presentation: Double-support time is the amount of time spent with both feet on the ground during one gait cycle. The percentage of time spent in double support may be increased in elderly persons and in those with balance disorders. The percentage of time spent in double support decreases as the speed of walking increases. 7/2/2012 dnbid71@gmail.com 6
PowerPoint Presentation: Stride length is the linear distance between two successive events that are accomplished by the same lower extremity during gait. In general, stride length is determined by measuring the linear distance from the point of one heel strike of one lower extremity to the point of the next heel strike of the same extremity (Fig. 14-10). 7/2/2012 dnbid71@gmail.com 7
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PowerPoint Presentation: The length of one stride is traveled during one gait cycle and includes all of the events of one gait cycle. Stride length also may be measured by using other events of the same extremity, such as toe-off, but in normal gait, two successive heel strikes are usually used. 7/2/2012 dnbid71@gmail.com 9
PowerPoint Presentation: A stride includes two steps, a right step and a left step. However, stride length is not always twice the length of a single step, because right and left steps may be unequal. Stride length varies greatly among individuals, because it is affected by leg length, height, age, sex, and other variables. 7/2/2012 dnbid71@gmail.com 10
PowerPoint Presentation: Stride length usually decreases in elderly persons and increases as the speed of gait increases. The length of one stride is traveled during one gait cycle. 7/2/2012 dnbid71@gmail.com 11
PowerPoint Presentation: Stride duration refers to the amount of time it takes to accomplish one stride. Stride duration and gait cycle duration are synonymous. One stride, for a normal adult, lasts approximately 1 second. 7/2/2012 dnbid71@gmail.com 12
PowerPoint Presentation: Step length is the linear distance between two successive points of contact of opposite extremities. It is usually measured from the heel strike of one extremity to the heel strike of the opposite extremity (see Fig. 14-10). A comparison of right and left step lengths will provide an indication of gait symmetry. 7/2/2012 dnbid71@gmail.com 13
PowerPoint Presentation: The more equal the step lengths, the more symmetrical is the gait. 7/2/2012 dnbid71@gmail.com 14
PowerPoint Presentation: Step duration refers to the amount of time spent during a single step. Measurement usually is expressed as seconds per step. When there is weakness or pain in an extremity, step duration may be decreased on the affected side and increased on the unaffected (stronger) or less painful side. 7/2/2012 dnbid71@gmail.com 15
PowerPoint Presentation: Cadence is the number of steps taken by a person per unit of time. Cadence may be measured as the number of steps per second or per minute, but the latter is more common: Cadence = number of steps/time 7/2/2012 dnbid71@gmail.com 16
PowerPoint Presentation: A shorter step length will result in an increased cadence at any given velocity. Lamoreaux found that when a person walks with a cadence between 80 and 120 steps per minute, cadence and stride length had a linear relationship. As a person walks with increased cadence, the duration of the double-support period decreases. When the cadence of walking approaches 180 steps per minute, the period of double support disappears, and running commences. 7/2/2012 dnbid71@gmail.com 17
PowerPoint Presentation: A step frequency or cadence of about 110 steps per minute can be considered as “typical” for adult men; a typical cadence for women is about 116 steps per minute. 7/2/2012 dnbid71@gmail.com 18
PowerPoint Presentation: Walking velocity is the rate of linear forward motion of the body, which can be measured in meters or centimeters per second, meters per minute, or miles per hour. Scientific literature favors meters per second. 7/2/2012 dnbid71@gmail.com 19
PowerPoint Presentation: In instrumented gait analyses, walking velocity is used, inasmuch as the velocities of the segments involve specification of direction: Walking velocity (meters/second) = distance walked (meters)/time (seconds) 7/2/2012 dnbid71@gmail.com 20
PowerPoint Presentation: Women tend to walk with shorter and faster steps than do men at the same velocity. Increases in velocity up to 120 steps per minute are brought about by increases in both cadence and stride length, but above 120 steps per minute, step length levels off, and speed increases are achieved with only cadence increases. 7/2/2012 dnbid71@gmail.com 21
PowerPoint Presentation: Speed of gait may be referred to as slow, free, and fast. Free speed of gait refers to a person’s normal walking speed; slow and fast speeds of gait refer to speeds slower or faster than the person’s normal comfortable walking speed, designated in a variety of ways. There is a certain amount of variability in the way an individual elects to increase walking speed. 7/2/2012 dnbid71@gmail.com 22
PowerPoint Presentation: Some individuals increase stride length and decrease cadence to achieve a fast walking speed. Other individuals decrease the stride length and increase cadence. 7/2/2012 dnbid71@gmail.com 23
PowerPoint Presentation: Step width , or width of the walking base, may be found by measuring the linear distance between the midpoint of the heel of one foot and the same point on the other foot (see Fig. 14-10). Step width has been found to increase when there is an increased demand for side-to-side stability, such as occurs in elderly persons and in small children. 7/2/2012 dnbid71@gmail.com 24
PowerPoint Presentation: In toddlers and young children, the center of gravity is higher than in adults, and a wide base of support is necessary for stability. In the normal population, the mean width of the base of support is about 3.5 inches and varies within a range of 1 to 5 inches. 7/2/2012 dnbid71@gmail.com 25
PowerPoint Presentation: Degree of toe-out represents the angle of foot placement (FP) and may be found by measuring the angle formed by each foot’s line of progression and a line intersecting the center of the heel and the second toe. The angle for men normally is about 7° from the line of progression of each foot at free speed walking (see Fig. 14-10). The degree of toe-out decreases as the speed of walking increases in normal men. 7/2/2012 dnbid71@gmail.com 26
PowerPoint Presentation: Power generation is accomplished when muscles shorten (concentric contraction). They do positive work and add to the total energy of the body. Power is the work or energy value divided by the time over which it is generated. 7/2/2012 dnbid71@gmail.com 27
PowerPoint Presentation: The power of muscle groups performing gait is calculated through an inverse dynamic approach. The power generated or absorbed across a joint is the product of the net internal moment and the net angular velocity across the joint. 7/2/2012 dnbid71@gmail.com 28
PowerPoint Presentation: If both are in the same direction (flexors flexing, extensors extending, for example), positive work is being accomplished by energy generation. The most important phases of power generation and absorption have been designated by joint (H= hip, K = knee, A= ankle) and plane (S = sagittal, F= frontal, T= transverse). 7/2/2012 dnbid71@gmail.com 29
PowerPoint Presentation: Power absorption is accomplished when muscles perform a lengthening (eccentric) contraction. They do negative work and reduce the energy of the body. If joint motion and moment are in opposite directions, negative work is being performed through energy absorption. 7/2/2012 dnbid71@gmail.com 30
PowerPoint Presentation: End of part - 2 7/2/2012 31 dnbid71@gmail.com