Body height change from motor vehicle vibration

Seventeen (17) subjects were exposed to tri-axial vehicle whole-body vibrat ion for approximately 3 h, and measured hourly for body height. The control was the same environment, but no vibration. A broad band predominantly z-a xis acceleration (1.6-10 Hz), with a mean level of 0.885 m/s(2) at the seat , was generated by a semi-truck tractor driven on secondary roads. The domi nant one-third octave band of the vibration at the seat was 2 Hz with an ac celeration magnitude of 0.521 m/s(2). At the end of the first hour, the res ults indicated a subject growth by 1.14 mm when exposed to vibration and a shrinkage of nearly equal amount without vibration. In the second and third hours, subjects followed the natural tendency to shrink under both conditi ons. At the end of the third hour, the subject height with vibration was 2. 23 mm higher than that without vibration.