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A new methodology for objective evaluation of discomfort in whole-body vibration (WBV) is introduced in this work. The proposed objective discomfort characterizes discomfort based on the relative motion between adjacent segments of the human body from neutral positions. It peaks when the joints reach their limits. The objective discomfort has been tested on five subjects in the fore-aft direction using discrete sinusoidal frequencies of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, 12, 14, and 16 Hz. Each frequency file runs for 15 s with a 3 s resting period as a reference for discomfort comparison. All files run at a constant acceleration of 0.7 m/s 2 . The subjects were tested with back support and without back support, and their subjective discomfort was reported based on the Borg CR-10 scale. The proposed objective discomfort has shown significant correlation with the subjective discomfort. The objective discomfort has also been tested on five subjects under multiple-axis random WBV with three common industrial seating configurations (seatmounted control, floor-mounted control, and steering wheel), and has shown promising results.

All-terrain vehicles (ATVs) require "active riding," meaning operators must rapidly assess changes in vehicle stability and adjust body position to compensate. No previous studies have reported using an ATV simulator to study active riding by human subjects. An ATV was mounted to a computercontrolled platform. Ride-file programs were developed which included sudden vehicle pitch (upward/downward) and roll (side to side) movements. A motion-capture system and accelerometers collected data that were analyzed with 3D modeling software. The posture and dynamic response to simulated sudden terrain changes for five adult males with ATV riding experience were determined. This study provides proof-of-principle for the use of ATV simulation to study active riding. In addition, the response patterns of experienced adult ATV operators can now be compared to that of other groups (e.g. inexperienced operators, children, drivers with passengers) to determine potential differences that might contribute to loss of vehicle control and crashing.

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The three-dimensional translational multi-input/output relative transmissibility and the transmissibility of supine humans during transportation were introduced in this work and were compared with the single-axis input/output condition. Eight healthy subjects were tested under multi-axis input/output whole-body vibration of white noise random signals with frequency content of 0.5-20 Hz and vibration magnitude of 1 m/s 2 RMS applied at the platform level, considering three immobilization conditions: rigid-platform, litter-board, and litter-board-collar. The results showed the diagonal components of the multiaxis input/out transmissibility and relative transmissibility to be considerably larger than their out-of-diagonal components. Significant correlations (R 2 > 0.93) were found between the diagonal components of the transmissibility of the multiaxis input/output and those of the individual single-axis input/output wholebody vibrations; however, weaker correlation (R 2 > 0.11) was shown between their cross-axis components.