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Modelling the apparent mass of the standing human body under whole-body vibration training conditions

Several studies have measured the vibration transmitted to and through the human body under vibration training conditions. However, no work has modelled the apparent mass of the human body under such conditions. In this work, a 2 degree-of-freedom model has been developed to predict the apparent mass of the standing human body under whole-body vibration training conditions. The parameters of the model were optimised using measured apparent mass of 12 subjects standing with different knee angle of 180°, 165°, 150° and 135°. Good agreement was found between the predicted and measured apparent mass with errors less than 3 kg in the median apparent mass magnitude and errors less than 6° in the apparent mass phase angle. The medians of the optimised parameters of the 12 individual apparent masses were close to the corresponding optimised parameters of the median apparent mass of the 12 subjects. Compared to standing with extended legs, bending the knees was found to affect mainly the parameters (i.e. stiffness and damping) of the model close to the source of vibration. Bending the knees decreased the mass of the model close to the source of vibration and increased the mass away from the source of vibration. Among the postures with bent knees, the change in the model parameters was generally not significant. The model can be used as a tool by manufacturers of whole-body vibration training machines to test the performance of the machines during the design stage and/or after production. This will decrease the number of experimentations with human subjects which guarantees consistency, repeatability, time-saving and safety.