Effects of Shoe Type and Walking Speed on Knee Joint Loads / 医用生物力学

Objective To investigate the effects of shoes type (barefoot, ordinary running shoes, minimalist shoes) and walking speed (jogging, walking at normal speed) on biomechanical parameters of knee joint, so as to provide theoretical reference for scientific fitness. Methods Vicon three-dimensional （3D） motion capture system and Kistler 3D force plate were used to collect biomechanical parameters of lower limbs from 10 subjects during walking at different speed with different shoes. Two-way (2 walking conditions × 3 shoe conditions) repeated measures analysis of variance was used to statistically analyze each dependent variable. Results Compared with jogging, the lateral excursion of plantar center of pressure (COP) was greater, the moment arm in frontal plane, the adduction moment and peak loading rate of knee joint were smaller, but the angular impulse of knee joint in frontal plane was greater. Compared with ordinary running shoes, the stride length was decreased, the lateral excursion of COP was greater, and the moment arm of knee joint in frontal plane, the knee adduction moment, the peak load rate and the angular impulse of knee joint in frontal plane were smaller. Conclusions In order to reduce the angular impulse and peak loading rate of knee joint in frontal plane, it is recommended to jog with small strides for ordinary people with minimalist footwear.

Analysis on postural stabilization from visual feedback through Brownian motion modeling / 医用生物力学

Objective To explore postural stabilization of visual feedback to human body and its mechanisms. Methods Displacement of the center of pressure (COP) of 12 healthy young adult volunteers were investigated under upright posture with and without visual feedback conditions. The Brownian motion model was employed to compare the differences in diffusion coefficients, Hurst exponents, and critical points of the COP trajectories under the above two conditions, and one way repeated measures ANOVA was utilized to test the significance of these differences. ResultsUnder the visual feedback condition, in long-term time intervals, diffusion coefficients were reduced by about two thirds and Hurst exponents reduced by half; in short-term time intervals, no significant differences were found in diffusion coefficients in the medial-lateral (ML) direction and in Hurst exponents; in addition, the coordinates of the critical points presented no statistically significant differences in the time intervals except for the mean square displacement in the anterior posterior (AP) direction. ConclusionsVisual feedback enhances the closed-loop control mechanism of postural control, while it does not have great impact on the open-loop control mechanism and transitional characteristics of the two mechanisms; moreover, the effect of visual feedback on postural control in AP direction is more obvious than that in ML direction.

Kinetic Characteristics during Initiation of Gait in Stroke Patients

OBJECTIVE: The aim of the present study was to understand biomechanical characteristics during the process of initiation of gait (IOG) from the standing position in hemiplegic patients. METHOD: We recorded the ratio of the vertical forces of both limbs to body weight and the movement of net center of pressure (COP) on two force platforms during the process of initiation of gait (IOG) from standing in 10 normal control and 10 hemiplegic patients and processed these data using ELITE DMA acquisition program. All data were collected with uninvolved limb and involved limb and compared each other by independent samples t-test. RESULTS: 1) In 10 hemiplegic patients, nine patients began taking a step with an uninvolved limb in the first, followed by an involved limb. 2) The period of IOG of the swing limb was 0.80 sec when patients walked with an uninvolved side and those of the stance limb was 1.60 sec with involved side. When the control group walked, the period of IOG of the swing limb was 0.70 sec and those of stance limb was 1.50 sec. The period of IOG of the swing limb in uninvolved side and those of the stance limb in involved side showed significant longer than control group. 3) The latency of IOG of swing and stance limb was significantly more prolonged than control groups. 4) Anteroposterior (AP) and mediolateral (ML) distance of net COP from release to unloading with uninvolved limb showed significant longer than control groups. 5) The velocity of net COP displacement from start to release with involved limb was significantly slower than control groups. CONCLUSION: This pattern of IOG could be used as one of the tools to evaluate postural control during gait training in the hemiplegic patients with gait disabilities, and it can be used as a basis for specific therapeutic intervention, and it allows evaluation of the effectiveness of treatment.

The Path of Center of Pressure(COP) of the Foot during Walking

Variations in the distribution and the magnitude of the forces in the foot may reflect painful conditions and abnormalities of structure or function. By tracking the path of the instantaneous COP(center of pressure) during stance phase, the balance and pattern of progression can be determined, but parameters on COP have not been standardized nor widely applied to clinical settings yet. To quantify the COP parameters and to evaluate the clinical applicability of COP, within subject experimental design was used. Twenty six subjects with age of sixties who had no history of foot problems were recruited. Foot contact and COP parameters were measured and compared between flat foot, low heel and high heel shod walking. 1) Gait cycle parameters, 2) foot contact parameters such as total contact area, contact length, contact width, and 3) COP parameters such as initial contact COP, mean COP, anteroposterior and mediolateral displacement of COP, slope of COP, velocity of COP during each functional rocker were measured with F-scan pressure sensitive insole system. In normal flat foot walking, COP of initial contact and mean COP were anatomically correspond to the center of the heel and to the center of the sole respectively. COP displacements corresponded to 83% of foot contact length anteroposteriorly and 18% of forefoot contact width mediolaterally. Slope of COP was about 6 degrees inwardly directed. Velocities of the COP during each functional rocker action were even and about 22-27 cm/sec around. In high heel shod walking, COP of initial contact was displaced 1.73 cm anteriorly and mean COP was displaced 0.31 cm medially and 1.89 cm anteriorly. Anteroposterior displacement of COP was also reduced. Velocity of the COP during heel rocker was faster and velocity during ankle rocker was slower compared to flat foot walking, which suggests excessive heel rocker and reduced ankle rocker action in high heel shod walking. In conclusion, COP parameters measured by pressure sensitive insole system may reflect the biomechanical alteration of the foot quantitatively and may be useful in assessing the biomechanical function of the foot.