Biological Responses to Local Vibratory Stimulation for the Lower Legs and Lower Back and Criterion Values Based on Sweep Frequencies of Healthy Individuals: An Observational Study

Declining proprioceptive function is associated with problems such as lower back pain and falls. Therefore, we developed a vibration device using sweep frequency to evaluate several proprioceptors with different response frequency ranges. This study aimed to elucidate the biological responses of healthy individuals to vibratory stimulation at different sites and frequency ranges and to propose cutoff values to determine the decline in proprioceptive function. Mechanical vibration was separately applied to the lower legs and lower back, and proprioceptive function was evaluated by defining the ratio of the center of pressure (CoP) in the anteroposterior direction during mechanical vibration to that during no vibration in the three frequency ranges. The cut-off value was defined as the mean value, with the standard deviation subtracted for each indicator. The cut-off values were higher in the lower legs than in the lower back at all frequency ranges and in the 30–53 Hz and 56–100 Hz frequency ranges for both the lower legs and lower back. In healthy individuals, 9.9% and 8.6% were below the cut-off values in the 30–53 Hz and 56–100 Hz frequency ranges for the lower legs, respectively.