VIBRATION TRANSMISSIBILITY OF MULTI-BODY SEGMENTS IN REACH MOVEMENTS UNDER WHOLE-BODY VIBRATION EXPOSURE Heon-Jeong Kim 1 and Bernard J. Martin 2 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, USA, heonjeon@umich.edu 2 Departments of Industrial and Operations Engineering, University of Michigan, Ann Arbor, Michigan, USA, martinbj@umich.edu INTRODUCTION Vehicle vibration is transmitted to the whole body of the seated driver and operators, thus causing discomfort and interfering with their movements in this dynamic environment. More specifically, vibration can affect the speed and accuracy of reaching and manipulating tasks associated with vehicle operations (Rider et al, 2003). Several studies have examined the effects of vibration on seated human to improve comfort, safety or performance. The apparent mass of the upper torso in static seated postures was analyzed as a function of vibration variables (Griffin, 1990), (Paddan and Griffin, 2002). Reach performance in ride motion was quantified by finger-tip trajectory and aiming error (Rider et al, 2003 and 2004). The present study investigates vibration transmissibility of multi-body segments along the transmission path, with the goal to develop an active biomechanical model for the proper evaluation of whole-body vibration (WBV) effects on reach performance. METHODS AND PROCEDURES A biodynamic reach experiment was conducted on the ride motion simulator (RMS) of the US Army to generate vehicle vibration. Six sinusoidal vibration inputs were produced by combining three vibration frequencies (2, 4, or 6Hz) and two vibration directions (vertical or fore-and-aft). Six participants performed self-paced reaches in a random order with one repetition to five targets representing the right reach hemisphere. Reach movements were recorded by an optical motion capture system (VICON) using twenty-six retro-reflective markers attached to selected body landmarks. Transfer functions of the torso, right upper arm, and right lower-arm-hand were estimated by Fast Fourier Transform (FFT) applied to motion capture data. Vibration transmissibility along the right arm was investigated by comparing peak perturbations of the right shoulder, elbow, and index finger. RESULTS As expected, the transfer functions along the right upper body segment vary as a function of vibration frequency (Figure 1 and 2). Vibration transmissibility along the right arm shows the same characteristics regardless of vibration direction such as vertical and fore- and-aft axis. Peak transmissibility increases from the right shoulder to the right index fingertip for the 2 Hz frequency, while it decreases along the right arm path for the 6 Hz frequency. For the 4 Hz frequency, the peak transmissibility decreases from the shoulder to the elbow and does change form the elbow to the finger. The peak transmissibility for individual upper body segments varies as a function of vibration direction as well as vibration