Assessment of Characteristics of Receptor Response to Vibration Stimuli

Abstract

We assessed the characteristics of receptor response for the purpose of developing a vibration stimulator and stimulation methods aiming to improve standing balance. Vibration detection thresholds and the degree to which the site of stimulation matches the site of perception were examined in 22 feet of 11 healthy adults (21.0±1.8 years). Stimulation was applied at a frequency of 225Hz using an original vibration stimulator comprising a frequency oscillator and piezoelectric element. Threshold was determined by averaging measurements obtained by ascending and descending methods. In the ascending method, the applied voltage was measured at the point at which vibration could be perceived, and in the descending method, the applied voltage was measured at the point at which vibration could no longer be detected. The concordance between the site of stimulation and the site of perception was determined by asking subjects to indicate the site at which vibration was perceived using the ascending method. Vibration thresholds were 6.6±3.6V at the base of the fifth metatarsal bone, 5.5±3.3V at the navicular bone, 7.8±3.8V at the lateral malleolus, 6.5±3.1V at the medial malleolus, and 11.9±4.5V at the head of the fibula. A significantly higher threshold was observed at the head of the fibula [F(4,105)=10.186, p<.001]. The site of stimulation and the site of perception matched, were nearby, and were unclear in 11, 8, and 3 feet, respectively, at the base of the fifth metatarsal bone;9, 9, and 4 feet, respectively, at the navicular bone;9, 7, and 6 feet, respectively, at the lateral malleolus;10, 4, and 8 feet, respectively, at the medial malleolus;and 9, 0, and 13 feet, respectively, at the head of the fibula. The degree of concordance was ‘unclear’(p<.05) at the base of the fifth metatarsal bone and ‘nearby’(p<.01) at the head of the fibula in a significantly smaller number of subjects, and was ’unclear’ at the head of the fibula in a significantly larger number of subjects. These results probably reflect the influence of the distribution of receptor density and vibration transmission to the surrounding soft tissues.