Generation of Kinesthetic Illusion and Tonic Vibration Reflex Response in Trunk Flexion and Extension Motion with Mechanical Vibration Stimulation

Mechanical vibration stimulation to muscles influences human motion through the phenomena of kinesthetic illusion (KI) and tonic vibration reflex (TVR). On the other hand, some people suffer from disability of their motor functions. Trunk flexion and extension are essential movements involved in many daily activities and often play a critical role in coordinating with limb motions. The effects of vibration stimulation on trunk muscles involved in flexion and extension might be applicable for the rehabilitation of the people suffer from disability of their motor functions. This research applies mechanical vibration stimulation to the trunk muscles for the aim of rehabilitation, measuring the resultant KI and TVR in the motion of trunk flexion and extension, comparing the outcomes across different vibration frequencies. INTRODUCTION Motor disorders caused by stroke and spinal cord diseases significantly impact the daily lives of many patients. Mechanical vibration stimulation has emerged as a promising technology in the field of motor rehabilitation. Mechanical vibration stimulation to muscles, which can induce phenomena such as kinesthetic illusion (KI) and the tonic vibration reflex (TVR), alters the contraction and proprioception of the stimulated muscles and is developing into a technique for human motion modification [1]-[4]. In recent years, many studies have focused on the application of mechanical vibration stimulation in the field of human assist robotics, such as perception assist [1], tremor suppression [2], rehabilitation exercises [3], and prosthetics [4]. KI is a phenomenon in which the stimulated muscle generates the sensation of performing joint movements related to its extension when mechanical vibration is applied to the muscle. In other words, by stimulating the antagonist muscles of a specific joint movement, a person can experience the sensation of performing that movement [5]. When muscles are subjected to vibration stimulation, the TVR phenomenon typically occurs simultaneously with the appearance of the KI phenomenon. TVR is a phenomenon of involuntary muscle contraction in response to vibration stimulation, first discovered by Eklund et al. in 1966 [6][7]. A great deal of prior research has already been conducted on the characteristics of KI and TVR. Roll et al. [8] observed that when vibrations within the range of 10-120 Hz are applied *Resrach supported by JST [Moonshot R&D] [Grant Number JPMJMS2034]. Y. Hou is with the Department of Mechanical Engineering Kyushu University, Fukuoka, 819-0395 Japan, (e-mail; hou.yue.455@s.kyushu- u.ac.jp). S. Nishikawa is with the Department of Mechanical Engineering Kyushu to unloaded biceps and triceps brachii muscles, the most significant illusion occurs at 70 Hz. Similarly, Naito et al. [9] conducted a study using vibrations between 10-240 Hz on the unloaded elbow joint and found that the most pronounced KI is elicited at frequencies of 70-80 Hz. Based on these findings, they proposed that the maximum intensity of KI in muscles without load can be achieved at around 70 Hz. Moreover, other vibration factors, such as amplitude and initial contact force, are also believed to influence both the threshold and intensity of KI [10]. Additionally, it is recognized that muscle tone, along with individual differences such as gender and dominant hand, also affect KI [11]. On the other hand, TVR is triggered by vibration stimulation with frequencies ranging from 20 to 300 Hz, with studies reporting that the magnitude of the reflex increases as the frequency rises [6]. Additionally, variations in reflex responses have been observed depending on the condition of the muscles receiving the vibration and individual differences between subjects [12]. This study investigates the potential of mechanical vibration stimulation on trunk muscles to induce KI and TVR in flexion and extension movements, aiming to develop rehabilitation technologies that enhance motor control and support recovery in individuals with movement impairments. So far, existing research on KI and TVR has primarily concentrated on the joints of the limbs, such as the shoulder, elbow, wrist, knee, and ankle [1]-[14]. However, many daily limb movements also involve simultaneous trunk movements, making it equally important to investigate the generation of KI and TVR responses in trunk joint movements. Despite its significance, this aspect of research has not been thoroughly investigated. As a foundational study aimed at motor rehabilitation, this research explores the KI and TVR responses induced by mechanical vibration stimulation applied to trunk flexion and extension muscles. Specifically, mechanical vibration stimulation was applied to the related trunk muscles individually to determine whether it could induce KI and TVR responses. Furthermore, different vibration frequencies were tested to evaluate whether frequency variations influence the degree of movement changes, contributing to the development of rehabilitation strategies. University, Fukuoka, 819-0395 Japan, (e-mail; nishikawa@mech.kyushu- u.ac.jp). K. Kiguchi is with the Department of Mechanical Engineering Kyushu University, Fukuoka, 819-0395 Japan, (phone: +81-92 -802-3236; fax: +81- 92-802-0001; e-mail: kiguchi@ieee.org). Generation of Kinesthetic Illusion and Tonic Vibration Reflex Response in Trunk Flexion and Extension Motion with Mechanical Vibration Stimulation Yue Hou, Student Member, IEEE, Satoshi Nishikawa, Member, IEEE, and Kazuo Kiguchi, Senior Member, IEEE 2025 IEEE/SICE International Symposium on System Integration (SII) January 21-24, 2025, Munich, Germany 979-8-3315-3161-4/25/$31.00 ©2025 IEEE 410