Time dependence and non-linearity of the impedance of the human hand-arm system while exposed to intense vibration.

The object of the investigation was to find out possible non-linearities and dependencies of the impedance of the hand-arm-system on the exposure time. The measurements were made on four male test persons, with the vibrations being introduced parallel to the forearm axis and in a standing position with the arms stretched. The vibration accelerations were between 11 m/s2 and 36 m/s2, and the measuring handle had a weight of only 48 g. The impedance decreases in dependence on time at maximum spanning force without pressing force. After 1 min of exposure time, values of about 55% are reached at 40 Hz and values of about 80% at 20 Hz. The impedance with pressing force of 100 N without spanning force increases with time, most distinctly at 25 Hz. No influence of the vibration intensity could be seen. The compression-tension quotient was introduced as characteristic for the non-linearity. It is dependent on the frequency, the vibration acceleration and, with large vibration accelerations, also on the exposure time. The quotient is 1 ... 1.5 at vibration accelerations up to 10 m/s2, and 3 ... 4 at vibration accelerations up to 36 m/s2 and after 3 to 5 min exposure time.