## 4 Discussion  
To our knowledge, this is the first study to evaluate the postural response when vibration was applied in the entire response frequency range of proprioceptors using sweep frequency. Our main finding was that NSLBP relied more on LM input in the Vater-Pacini corpuscles during vibratory stimulus with a sweep frequency of 168-247 Hz to the lower leg in the standing position. Past studies have already demonstrated that elderly patients with LBP relied on trunk strategies (Vater-Pacini corpuscles) for postural control during vibratory stimulation [15; 16]. Compared with NLBP, lower RPW values in NSLBP during vibratory stimulations of 168 to 247 Hz indicate that NSLBP relies on trunk-muscle proprioceptive inputs. Moreover, the reduction in lower leg sensitivity at the Vater-Pacini corpuscles in the NSLBP group agrees well with the result of previous studies which reported that the NSLBP group decreased its reliance on proprioceptive signals from the lower leg during standing at 240 Hz of constant vibratory stimulus [15; 16]. However, statistically significant differences were not observed between the NLBP and NSLBP groups in the Meissner corpuscles and muscle spindle. The decreased reliability on LM inputs in the Meissner corpuscles and muscle spindle may not have been recognized in the NSLBP group because this study was performed under different conditions from measurement methods and subjects in the previous studies [10; 11; 12; 21; 22; 23; 24]. In addition, the differences in age and LBP degree may have affected even the same cases of disease [15; 16]. Therefore, the NSLBP group may depend more on the Vater-Pacini corpuscles of their trunk than on the Meissner corpuscles and muscle spindle. Second, the resulting RMS values were considered. A significant interaction between the NLBP and NSLPB groups and the stimulated body location in Vater-Pacini corpuscles was confirmed. From Figure 3, the NSLBP group exhibited higher RMS values when vibration in the frequency band of the Vater-Pacini corpuscles was applied to LM. This result supports that the NSLBP group relied more on LM input in the Vater-Pacini corpuscles for postural control. These results agree well with those of previous studies where significant differences in postural sways were found between elderly individuals and healthy young adults during quiet standing conditions [25]. Moreover, a decreasing trend in the proprioceptive function in lower leg was observed in the NSLBP group. These findings clearly show the differences in postural control strategies of proprioceptive inputs with respect to NSLBP, suggesting that LBP may influence the postural control strategy of proprioceptive inputs derived from the Vater-Pacini corpuscles of the LM. For the above reasons, we confirmed that the function of the Vater-Pacini corpuscles was decreased in relation to LBP using the sweep frequency method. [PERSON] et al. reported that patients with NSLBP may have even greater postural instability because the sensitivity of GS at 240 Hz continues to decline [15]. Thus, the reduction possibly causes postural instability because the NSLBP group cannot switch to a more appropriate proprioceptive postural strategy. In addition, the effect of RPW on postural control under proprioceptive stimulation with the response frequency of Vater-Pacini corpuscles may be a good indicator of evaluating the degree of LBP under the sweep frequency method, same as the constant frequency method used in our previous study [15]. These findings could be used to diagnose NSLBP due to the reduced function of proprioceptors. The advantages of using the sweep frequency are as follows. Firstly, the sweep frequency method may eliminate individual differences in the response frequency of proprioceptors. Secondly, the resolution is high because the vibration is applied to the entire frequency band of the response frequency of each proprioceptor. In the future, it may be possible to conduct more detailed proprioceptive examination by analyzing finer frequency bands.