A design of experiments for statistically predicting risk of adverse health effects on drivers exposed to vertical vibrations.

An injury risk factor (IRF), which indicates the risk of adverse health effect to lumbar rachis arising from mechanical vibrations, is developed. Experiments have been conducted that consider acceleration levels at the seat of drivers, posture, morphology, density, damping rate and body mass as independent variables. A parametric finite-element model of the lumbar rachis has been generated. It is shown that the IRF increases with ageing and an IRF of 30% is proposed as a threshold for fatigue purposes. This level is reached if a peak acceleration level greater than 3 m/s² is applied to a light (55 kg) and an old driver with a low bone density and a damping rate of 20%. This vibration threshold must be reduced to 2.7 m/s² if the driver?s weight increases to 75 kg and to 2 m/s² if the driver is heavy (98 kg).

Gesture as an important factor in 3D kinematic assessment of the knee.

Contradictions exist between studies of the 3D kinematics of the knee. We hypothesize that they are in part due to differences in the gesture performed by the subjects during kinematic assessment. The purpose of this study is to evaluate the impact of gesture variations on knee kinematics. Seventeen healthy male subjects performed 20-s series of knee-bends in a knee-bend standardizing structure. All series differed regarding either foot rotation, knee excursion, or hip rotation. 3D knee kinematics were recorded using optical position sensors mounted on a skin-motion-reducing harness. Kinematic comparisons were made between a gesture of reference (the standard gesture) and every other gesture. Analyses were performed on average differences. Differences of up to 15 degrees of tibial rotation were found for gestures involving different foot rotation. Gestures involving different knee excursion brought on differences of more than 4 degrees of tibial rotation while hip rotation induced more than 5 degrees of tibial rotation. It is hereby demonstrated that gesture differences can have a dramatic impact on measured knee kinematics. Hence gesture performance needs to be carefully monitored during 3D kinematic assessment of the weight-bearing human knee.

Gesture standardization increases the reproducibility of 3D kinematic measurements of the knee joint.

BACKGROUND: The literature on the 3D kinematics of the knee suggests that the gesture accomplished during kinematic assessment might play a significant role in the values measured. The purpose of this study is to demonstrate that a standardized gesture leads to an increased reproducibility in 3D kinematic measurements of the knee. METHODS: Seventeen healthy male subjects performed series of knee-bends in standardized and unconstrained conditions while their left knee's 3D kinematics were recorded using an optical motion-recording system. Standardized knee-bends were performed in a specially designed structure stabilizing the shoulders, pelvis and feet. Coefficient of multiple correlation were calculated for the ascent and the descent phases of the knee-bends for the tibial rotation and abduction/adduction components of the knee movement. FINDINGS: Comparisons between coefficient of multiple correlation of the different gesture conditions showed a statistically significant increase in reproducibility for the tibial rotation during the standardized knee-bends. INTERPRETATION: It appears that gesture standardization is an interesting option to consider for precise kinematic assessment of the living human knee.