Uncontrolled manifold analysis of gait variability : effects of load carriage and fatigue

The uncontrolled manifold (UCM) analysis has been demonstrated to be a powerful tool for understanding motor variability. The purpose of this study was to use the UCM analysis to investigate the effects of load carriage and fatigue on gait variability. Whole-body kinematic data during treadmill walking were collected from 12 healthy male participants when fatigue and load carriage were applied. The task-level variable for the UCM analysis was selected to be the whole-body COM. We chose to analyze the whole-body COM data at two important gait events: right heel contact and right toe off, and the UCM analysis was carried out in the sagittal and frontal planes, separately. The dependent measures were UCM variability measures and UCM ratio. Three-way ANOVA was performed to determine the main and interaction effects of back-carrying load, fatigue, and gait events on the dependent measures. The results showed that frontal UCM ratio significantly changed with the application of back-carrying load and fatigue, indicating that both factors had effects on motor performance in stabilizing the whole-body COM in the frontal plane. These findings can facilitate a better understanding of the nature of motor variability due to load carriage and fatigue

Lower-extremity bracing can improve postural stability during walking

Falls are a major cause of injuries and fatalities. In order to avoid a fall, it is essential to maintain postural stability. The purpose of this study was to evaluate wearing lower-extremity supports as a fall prevention intervention to improve postural stability. Eleven older participants participated in this study. These participants were instructed to walk on a treadmill at their comfortable speeds under five testing conditions: no support, ankle support, calf support, knee support, and thigh support. Postural stability during walking was quantified by local dynamic stability measures derived from non-linear dynamics. The results showed that wearing the thigh support and ankle support can lead to improved local dynamic stability in the frontal plane and sagittal plane, respectively. Therefore, it might be concluded that wearing the thigh support and ankle support may be an effective fall prevention intervention for reducing fall risks. In addition, wearing lower-extremity support is also a practical fall prevention solution since lower-extremity supports are ease of use and cost effective

Modelling 3D control of upright stance using an optimal control strategy

A 3D balance control model of quiet upright stance is presented, based on an optimal control strategy, and evaluated in terms of its ability to simulate postural sway in both the anterior–posterior and medial–lateral directions. The human body was represented as a two-segment inverted pendulum. Several assumptions were made to linearise body dynamics, for example, that there was no transverse rotation during upright stance. The neural controller was presumed to be an optimal controller that generates ankle control torque and hip control torque according to certain performance criteria. An optimisation procedure was used to determine the values of unspecified model parameters including random disturbance gains and sensory delay times. This model was used to simulate postural sway behaviours characterised by centre-of-pressure (COP)-based measures. Confidence intervals for all normalised COP-based measures contained unity, indicating no significant differences between any of the simulated COP-based measures and corresponding experimental references. In addition, mean normalised errors for the traditional measures were < 8%, and those for most statistical mechanics measures were 3–66%. On the basis these results, the proposed 3D balance control model appears to have the ability to accurately simulate 3D postural sway behaviours

Association between Crash Attributes and Drivers’ Crash Involvement: A Study Based on Police-Reported Crash Data

Understanding the association between crash attributes and drivers&rsquo; crash involvement in different types of crashes can help figure out the causation of crashes. The aim of this study was to examine the involvement in different types of crashes for drivers from different age groups, by using the police-reported crash data from 2014 to 2016 in Shenzhen, China. A synthetic minority oversampling technique (SMOTE) together with edited nearest neighbors (ENN) were used to solve the data imbalance problem caused by the lack of crash records of older drivers. Logistic regression was utilized to estimate the probability of a certain type of crashes, and odds ratios that were calculated based on the logistic regression results were used to quantify the association between crash attributes and drivers&rsquo; crash involvement in different types of crashes. Results showed that drivers&rsquo; involvement patterns in different crash types were affected by different factors, and the involvement patterns differed among the examined age groups. Knowledge generated from the present study could help improve the development of countermeasures for driving safety enhancement

Influence of Load Knowledge on Biomechanics of Asymmetric Lifting

Background: Load knowledge has been identified as a factor affecting the risk of low back pain (LBP) during symmetric lifting. However, the effects of load knowledge in asymmetric lifting tasks have not been reported yet. The purpose of this study was to investigate the load knowledge influence on lifting biomechanics in asymmetric lifting tasks; Methods: Twenty-four male adults were recruited to complete a psychophysical lifting capacity test and a simulated asymmetric lifting task. The lifting task was set with load knowledge of &lsquo;no knowledge&rsquo; (NK), &lsquo;weight known&rsquo; (WK), &lsquo;fragile material known&rsquo; (FK), and &lsquo;weight and fragile material known&rsquo; (WFK) for different lifting load weights. Trunk kinematics and kinetics were collected and analyzed; Results: When fragility information was presented, trunk sagittal flexion acceleration, lateral flexion velocity and acceleration, and average lateral bending moment were significantly lowered at the deposit phase. Lifting a high load weight was found to significantly increase low back sagittal bending moment at the lifting phase and low back moments of all three dimensions at the deposit phase; Conclusions: The decrease of trunk kinematic load suggests that providing material fragility information to workers in asymmetric lifting tasks would be effective in reducing their risk of LBP

Differences in lower extremity muscular responses between successful and failed balance recovery after slips

The main purpose of this study was to examine the differences in lower extremity muscular responses between successful and failed balance recovery after slips, and across different muscle groups. Twenty-five young healthy participants were recruited who were instructed to walk on a linear walkway, and slips were induced unexpectedly during walking. Four lower extremity muscle groups in both legs were examined here, including the tibialis anterior, medial gastrocnemius, rectus femoris, and medial hamstring. Lower extremity muscular responses were quantified by muscular activation latency, muscular peak amplitude, time-to-peak, and co-contraction index. The results showed that successful balance recovery was associated with smaller muscular peak amplitude and smaller time-to-peak in the rectus femoris of the perturbed leg compared to failed balance recovery. In addition, it was also found that the muscular activation latency in the medial hamstring of the perturbed leg was significantly smaller than those in the tibialis anterior, rectus femoris, and medial hamstring of the unperturbed leg. These findings can aid in better understanding fall mechanisms due to slips and be used to establish guidelines for developing fall prevention strategies in the workplace

Evaluation of Force-Time Curve Analysis Methods in the Isometric Mid-Thigh Pull Test

The purpose of this study was to evaluate the manual and automatic analysis methods for force-time curve analysis of the isometric mid-thigh pull (IMTP) test. The visual analysis, first derivative analysis and threshold analysis methods were used to analyse onset time and time-specific forces at 50 ms, 90 ms, 200 ms and 250 ms on the force-time curve. Ninety-three collegiate sports athletes’ trials were selected and analysed by each method. The visual analysis method was set as the reference method for paired comparisons with the first derivative analysis method and threshold analysis method. Onset time comparisons revealed that the first derivative analysis method was comparable with the visual analysis method with average difference at about 30 ms. Results from the weighted least products regression analysis and the Bland-Altman analysis showed that large fixed bias confounded by proportional bias existed in the threshold analysis method, and time-specific force variables obtained from the first derivative analysis method were closer to those from the visual analysis method when compared with the threshold analysis method. These findings suggest that the first derivative analysis method could be an effective tool for force-time curve analysis of the IMTP test

Predicting Errors, Violations, and Safety Participation Behavior at Nuclear Power Plants

Commissioning workers at nuclear power plants have long been ignored in previous studies, although their performance is closely related to the overall safety of plants. This study aimed to explain and predict three types of behavior, i.e., errors, violations, and safety participation, of commissioning workers, under the general framework of the theory of planned behavior (TPB) and by considering organization and planning factors. The validity of the model was evaluated with a sample of 167 commissioning workers who completed a self-reported questionnaire. The results showed that perceived behavioral control, along with organization and planning, significantly affected all types of behavior. It was also found that violations and errors were a direct result of attitude. Besides, errors were predicted by subjective norm; unexpectedly, this occurred in a positive way. These findings revealed the underlying mechanisms for the development of errors, violations, and safety participation among commissioning workers and provided practical implications for safety improvement at the commissioning workplace