Vibration sensitivity thresholds: methodological considerations

Vibration sensitivity thresholds were studied in 12 healthy volunteers using 25, 50, 100 and 250 s-1 stimulus frequencies from an instrument with automated and manual modes ('Vibra Mk II'). For the automated mode, a forced choice principle was adopted. All measurements were performed from both the knuckle of the IInd metacarpophalangeal joint and the medial malleolus on four successive days. In addition, a conventional tuning fork method for vibration sensitivity was applied. The results show high interindividual and intraindividual variation in all measurements. The threshold values measured by the automated system were significantly lower than those by manual system at all frequencies. The largest variation was seen at 250 s-1 and the most uniform values at 100 s-1. There was a clear difference between the values from knuckle and medial malleolus, the values in the foot being lower. There was no learning effect. Clear age-related increase in vibration thresholds was observed. Conventional tuning fork-method showed clear differences in vibration sensitivity between hand and foot, in accordance with computer assisted method. The higher sensitivity of the automated method compared to the manual makes this the method of choice, although further investigations to finish the method and to build up a broader reference material is desirable.