Lec2 Biomechanics PDF

Functional Tasks of Gait From a functional perspective, there are three fundamental tasks associated with human gait: weight acceptance, single limb support, and limb advancement. The stance phase plays a role in all three of these basic tasks, each of its sub-phases contributing to varying degree...

Functional Tasks of Gait From a functional perspective, there are three fundamental tasks associated with human gait: weight acceptance, single limb support, and limb advancement. The stance phase plays a role in all three of these basic tasks, each of its sub-phases contributing to varying degrees. Initial contact and loading response are the two sub- phases primarily responsible for weight acceptance. Single limb stance occurs at midstance and is the time when balance during ambulation is most precarious. The body’s center of mass has shifted laterally and is centered over only one supporting limb at this time. Limb advancement creates forward motion of the body and includes the stance sub- phases of terminal stance and preswing; these sub-phases provide propulsive forces to move the limb forward and thereby move the body forward. The stance sub-phases utilize effective force absorption and efficient energy expenditure to accomplish these tasks. The swing phase is concerned with only one of the three fundamental tasks: limb advancement. Limb advancement during the swing phase requires sufficient clearance of the foot from the floor. The limb performs this activity during the first half of swing and prepares for initial contact during the latter half of swing. During the first two sub-phases of the swing phase, initial swing and midswing, the limb flexes at the hip, knee, and ankle to functionally shorten the limb so the foot clears the floor. The knee then begins rapid extension in terminal swing to lengthen the limb; this motion increases step length and forms a rigid limb in preparation for stability at initial contact.  Analysis of gait Analysis of gait classified into: 1- Kinematic analysis 2- Kinetic analysis 1- Kinematic analysis: Kinematics is the science of motion. In human movement, it is the study of the positions, angles, velocities, and accelerations of body segments and joints during motion. It classified into 3 categories: Distance and time variables, Joint angles from sagittal and frontal plane for upper and lower limbs 1- Distance and time variables: Distance variables (spatial parameters): Step length: It is the linear distance between the initial contact (measured at the midpoint of the heel) of one foot to the initial contact of the opposite foot. Step length Values for normal adult’s step length are: 64 cm average for women, 73 cm average for men, and the overall average is 70.5 cm. Stride length: It is the linear distance between two successive foot contact of the same limb. It consists of two step lengths, left and right, each of which is the distance by which the named foot moves forward in front of the other one. It is usually measured from the midpoint of heel Stride length Values for normal adult’s stride length are: 128 cm average for women, 146 cm average for men, and the overall average is 141 cm. However, stride length is not always twice the length of a single step because right and left steps may be unequal. Stride width: It is the horizontal linear distance between the midpoint of the heel of one foot and the same point of the other foot. Step width measures typically between 2.5 to 12.5 cm for adults with the average of 8 cm; this standard does not hold true in some pathological conditions. Degree of toe out: It is the angle formed by each foot’s line of progression and a line intersecting the center of heel and the second toe. Out-toeing of about 7° is typical in mature adults. The degree of toe out decreases as the speed of walking increases in normal adults. Degree of toe out Time variables (Temporal parameters) Step time: it is time spent during single step between heel strike of one leg and heel strike of the other leg. Stride time: It is the time interval between successive instant of foot floor contact of the same foot. (i.e. it is the amount of time it takes to complete one stride). Stance time: It is the time that passes during the stance phase of one limb in a gait cycle. Swing time: It is the time while the foot is not in contact with the floor. (0.4 sec.) Single limb time: it is the time when only one limb is on contact with the supporting surface. Double limb time: it is time spent with both feet on the ground during one gait cycle. It decreases as the speed of walking increases. Swing / stance ratio: It is the ratio between swing time and stance time Cadence: It means number of steps per minute. (110 steps /min) Slow: 60 – 70 Steps / min. Medium: 80 – 90 Steps / min. Fast: 120 Steps / min. A shorter step length will result in an increased number of steps at a constant distance. As one walks with increased cadence, the duration of the double limb stance decreases. Speed: It is distance / time. - In male: 89 meter/min. - In female: 74 meter/min. (45 cm / sec) By increasing speed, the cadence, step length, stride length, single limb time, and swing time will increase. By decreasing speed, the stride width, stance time, and double limb time will decrease.  2- Measurement of joint angles The kinematics, or “geometry,” of walking has been studied and recorded, looking at the angular movements of each body segment in all three planes. Advances in photographic techniques and computer technology have permitted more accurate study from a three-dimensional perspective. Since the sagittal plane motions are the largest and easiest to track, they have been most often investigated. On the other hand, displacement in the frontal and transverse planes is smaller and more difficult to measure; therefore, results are less accurate and reliable and more divergent and inconsistent. Sagittal Plane kinematics In the sagittal plane, the two vertical oscillations of the body’s COM follow a smooth sinusoidal curve. The curve’s highest point occurs at midstance for each foot while the lowest segment of the sinusoidal curve is at double support. PELVIS The pelvis must multifunction during gait, providing both stability and mobility to upper and lower extremities. The pelvis offers a stable base of support for the lower limb and HAT but it also must allow for the contributions of thoracic and lumbar spine motions. Additionally, the pelvis must be stable enough to transmit weight as it transfers from one limb to the other, and it also needs to move the acetabulum in a favorable position for hip motion. In the sagittal plane, the pelvis remains relatively level, demonstrating an average anterior-posterior tilt excursion of only about 3° during the gait cycle. Two full cycles of sinusoidal motion occur with each step; the pelvis reaches initial contact in a near-neutral position and moves through midstance in a slightly posteriorly tilted position. By the end of midstance when the hip begins moving into extension, the pelvis tilts anteriorly just slightly. By the time the limb reaches preswing, the pelvis tilts posteriorly again. During swing, the pelvis first completes its posterior tilt and then tilts anteriorly from initial to midswing, and in terminal swing it moves toward a posterior tilt in preparation for landing once again. Hip joint The hip joint moves through 40° of sagittal motion in a single gait cycle. At initial contact, the hip is flexed at 25° to 30°.As the stance phase continues, the hip progressively moves into extension, reaching its maximum extension at 10° of hyperextension by terminal stance. From initial contact to midstance, the trunk moves forward over the foot and continues its forward movement to advance in front of the foot immediately after midstance. Hip hyperextension at terminal stance is accompanied by extension of the lumbar vertebrae and an anterior pelvic tilt. Once the hip reaches maximum extension at terminal stance, the hip begins movement towards flexion during preswing as it prepares to lift the limb off the ground; by the end of stance, the hip is near neutral, and as the limb begins into the swing phase, the hip continues a steady increase into flexion until midswing when the hip is slightly more than 30° of flexion. After midswing, its flexion decreases slightly and is maintained until terminal swing when it starts to move towards extension in preparation for initial contact. These typical sagittal plane arcs that occur at 10° of hyperextension (at terminal stance) and at 30° of flexion (at midswing) occur during normal walking speed but are slightly higher in fast walking. Clinical note: because pelvis and lumbar spine motions are mechanically linked at sacroiliac joint, exaggerated pelvic tilting during walking may increase the stress at lumbar spine. These stresses could eventually irritate the structures within this region resulting in low back pain Summary of hip joint: Hip Stance phase Swing phase joint IC LR MSt TSt * PSw Isw MSw * TSw 30º 25º 0º 10º 0º 20º 30º 30º flexion Flexion hyperextension flexion flexion flexion TSt: hyperextension arc, MSw: flexion arc Note: hip extension arc acts to transfer weight to contralateral limb, while hip flexion arc acts to clear foot from the ground.