Investigation of the functional decline in proprioceptors for low back pain using the sweep frequency method

The purpose of this study was to investigate the functional decline in proprioceptors in patients with low back pain (LBP) by evaluating the entire range of response frequencies of proprioceptors. In previous studies, the function of proprioceptors was only evaluated by single frequency vibrations. However, because it is assumed that individual differences exist in response frequencies of proprioceptors, we developed a method using vibration with sweep frequency covering the entire range of response frequencies of proprioceptors. The center of pressure was determined in 35 elderly patients with non-specific LBP (NSLBP) and 28 elderly individuals with non-LBP (NLBP) during upright stances on a balance board without vision. Local vibratory stimulations to lower leg or trunk muscles were continuously varied between 27 and 272 Hz over 60 s to evaluate the proprioceptive predominance of a body location using the relative proprioceptive weighting ratio (RPW). Compared with the NLBP group, the NSLBP group exhibited a lower RPW value for the Vater-Pacini corpuscles. Thus, the NSLBP group relied more on the input of Vater-Pacini corpuscles in the trunk. A reduction in lower leg sensitivity at the Vater-Pacini corpuscles in the NSLBP group was observed.