Distribution of mechanical impedance at the fingers and the palm of the human hand.

A comprehensive understanding of the complex biodynamic response of the human fingers-hand-arm system may help researchers determine the causation of injuries arising from hand-transmitted vibration. This study theoretically demonstrates that the mechanical impedance (MI) in a hand power grip, as a measure of the biodynamic response of the system, can be divided into finger MI and palm MI. A methodology is developed to measure them separately and to investigate their distribution characteristics. This study involves 6 adult male subjects, constant-velocity sinusoidal excitations at 10 different discrete frequencies (16, 25, 40, 63, 100, 160, 250, 400, 630, 1000 Hz), and three different hand-handle coupling conditions. Our results suggest that at low frequencies (40 Hz), the palm MI is substantially higher than the finger MI; the majority of the hand MI remains distributed at the palm up to 100 Hz; and at frequencies higher than 160 Hz, the finger MI is comparable to or higher than the palm MI. Furthermore, at frequencies equal to or above 100 Hz, the finger MI is practically independent of the palm-handle coupling conditions. Knowledge of the MI distribution pattern may increase the understanding of vibration transmission to the hand and aid in the development of effective isolation devices.