A possible basis for the risk assessment for hand-transmitted vibration may be to determine the amount of energy absorbed in the human hand and arm. In the present study, the mechanical energy absorption in the hand-arm system was measured within the frequency range of 4 to 1000 Hz. The study was carried out on ten healthy subjects during exposure to sinusoidal vibration. The influence of various experimental conditions, such as vibration direction (X _h , Y _h , Z _h ), grip force (25ndash;75 N), vibration level (8–45 mm/S_rms), and hand-arm posture were studied. The outcome shows that the energy absorption in the human hand and arm depended mainly on the frequency and direction of the vibration stimulus. Higher vibration levels, as well as firmer handgrips, resulted in higher absorption of energy. Varying hand-arm postures had only a small influence on the amount of absorbed energy, while the constitution of the hand and arm affected the energy absorption to a larger extent

The impulse response to vibration (0.5-400 Hz, 0.001-1.0 mm) was recorded from single mechanoreceptive afferents innervating the glabrous skin of the human hand. Needle electrodes inserted into the median nerve were used for the recording. The four types of mechanoreceptive afferents (FA I, FA II, SA I, and SA II) exhibited different response characteristics. Fast adapting units were the most easily excited at frequencies between about 5 to 50 Hz (FA I) and above about 50 Hz (FA II). The sensitivity of the slowly adapting units (SA I and SA II) was greatest at lower frequencies. Unit thresholds at 2, 20, and 200 Hz were measured before and after 2 min of powerful vibration exposure. Corresponding psychophysical thresholds were also measured during the recording of responses from single units. An acute but temporary depression in sensitivity occurred in the FA I, FA II, and SA I units as a consequence of the exposure. The magnitude and the time courses of the recovery of the encountered unit threshold shifts were approximately the same as those for the corresponding psychophysical threshold shifts. It was concluded that acute impairments of the tactile sensibility caused by vibration exposure, as observed in psychophysical studies, can probably be explained by an influence on the excitability of the tactile units.

The perception thresholds for vibration stimuli of the hand at seven frequencies (8-500 Hz) were evaluated in 300 patients referred to the Department of Hand Surgery in Malmö during the years 1985-1990 for various types of neuropathy (carpal tunnel syndrome, vibration-induced neuropathy, cervical rhizopathy, brachialgia, ulnar neuropathy, radial tunnel syndrome, and polyneuropathy). A sensibility index was calculated by dividing the integrated area under the obtained vibrogram curve of each object tested (area¹) by that of the corresponding area under a superimposed and age matched reference curve (area^R). Sensibility index of less than 0.8 was regarded as the cut off value. The index and little fingers bilaterally were tested to reflect median and ulnar nerve function. There were considerable variations in patterns of pathology among the various groups of patients. In patients with unilateral carpal tunnel syndrome only 10 patients (23%) had abnormalities limited to one recording, while 21 patients (47%) showed abnormalities in all four recordings. This indicates that an isolated carpal tunnel syndrome may reflect more generalised disease of the peripheral nervous system.