Biomechanical Analysis of Anticipatory and Reactive Locomotor Adjustments when Walking Onto a Moving Surface
Date Issued
2009
Date
2009
Author(s)
Hsu, Wei-Chun
Abstract
Causes of fall are complex and involve both human and environmental factors. Adapting our gait to cope with a predictably moving surface is a common fact of life in modern cities. Loss of balance or riders who were stuck by other passengers especially when steeping onto a moving walkway or escalators can lead to serious injuries. Awareness of the risks and the circumstances leading to those injuries allows for better direction of intervention strategies for injury prevention. However, the biomechanical strategies when walking onto a moving surface remained unexplored. Fifteen young subjects were recruited to participate in the study. Test conditions included walk along the walkway from the ground onto a moving surface (MS) or onto a static surface (SS). Subjects were instructed to initiate their gait from one end of the walkway through the movable walkway to the other end while kinematic and kinetic data were measured with a Vicon system and two forceplates. End point variables, joint angles, moments and power of the lower limbs as well as motion of the centere of mass (COM) and pelvis were calculated. The differences between surface conditions were analyzed using paired t-test (α=0.05). Compared to the baseline data in the SS condition, anticipatory locomotor adjustments (ALAs) to walk onto a moving surface started as early as the trailing heel-strike (T3) and mainly occurred during swing phase of the leading limb (T4-T5). With increased leading step speed and length but decreased trailing step speed and length during the anticipatory stride, decreased leading toe clearance and foot angle were found during the late leading swing phase which was longer. Compared to those in the SS condition, smaller ankle plantar flexor and hip abductor moments during the late stance suggested that not the muscular strength but proper temporal-spatial controls of locomotor system were essential to achieve a safe and smooth landing for the young subjects. Greater heel horizontal velocities, efficiency of work revealed by greater trailing ankle power and angular velocities were also observed during late anticipatory phase. ALA of COM acceleration occurred in the vertical and anterioposterior (A/P) directions at the end of leading SLS and trailing SLS (T5) when walking onto a moving surface to have position and velocity of COM decreased until the mid-swing and then increased at terminal swing in vertical and A/P directions. However, changes in COM accelerations might result in the more jerky motion of the body COM and thus lead to greater challenge in the control of the motion of COM. After T5, reactive adjustments revealed by altered heel contact dynamics were achieved through increased leading hip and knee flexion together with more anterior-flexed pelvis and plantar-flexed ankle. With greater initial A/P and M/L COM velocities and the forward moving surface, overall stability of the body in terms of the ROM of the COM was greater in the A/P and M/L direction during the reactive DLS, but inconsequence position of COM were overshot anteriorly and laterally to the leading side. To maintain dynamic stability, initial accelerations became smaller shortly after T5 and remained small during the reactive DLS. Faster weight-transferring but earlier break of accelerations were both essential for a safe walking landing with a. jerky motion during DLS. Knowledge of the ALA and reactive adjustments in compensating for moving surface in young subjects was established and that could be served as a baseline data for the management of other populations with balance deficits in the future. It was also suggested that training programs for patients who is at risk of fall should considered not only task-oriented management but also speed specific modulation.
Subjects
gait analysis
moving surface
kinematics
kinetics
anticipatory locomotor adjustments
reactive locomotor adjustments
Type
thesis
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