Visual and Vestibular Inputs Affect Muscle Synergies Responsible for Body Extension and Stabilization in Sit-to-Stand Motion

Abstract

The sit-to-stand motion is a common movement in daily life and understanding the mechanism of the sit-to-stand motion is important. Our previous study shows that four muscle synergies can characterize the sit-to-stand motion, and they have specific roles, such as upper body flexion, rising from a chair, body extension, and posture stabilization. The time-varying weight of these synergies are changed to achieve adaptive movement. However, the relationship between sensory input and the activation of the muscle synergies is not completely understood. In this paper, we aim to clarify how vestibular and visual inputs affect the muscle synergy in sit-to-stand motion. To address this, we conducted experiments as follows. Muscle activity, body kinematics, and ground reaction force were measured for the sit-to-stand motion under three different conditions: control, visual-disturbance, and vestibular-disturbance conditions. Under the control condition, the participants stood without any intervention. Under the visual-disturbance condition, the participants wore convex lens glasses and performed the sit-to-stand motion in a dark room. Under the vestibular-disturbance condition, a caloric test was performed. Muscle synergies were calculated for these three conditions using non-negative matrix factorization. We examined whether the same four muscle synergies were employed under each condition, and the changes in the time-varying coefficients were determined. These experiments were conducted on seven healthy, young participants. It was found that four muscle synergies could explain the muscle activity in the sit-to-stand motion under the three conditions. However, there were significant differences in the time-varying weight coefficients. When the visual input was disturbed, a larger amplitude was found for the muscle synergy that activated mostly in the final posture stabilization phase of the sit-to-stand motion. Under vestibular-disturbance condition, a longer activation was observed for the synergies that extended the entire body and led to posture stabilization. The results implied that during human sit-to-stand motion, visual input has less contribution to alter or correct activation of muscle synergies until the last phase. On the other hand, duration of muscle synergies after the buttocks leave are prolonged in order to adapt to the unstable condition in which sense of verticality is decreased under vestibular-disturbance.

Artificial neural network that modifies muscle activity in sit-to-stand motion using sensory input

“…Scholz et al also showed that how much sensory input can be used affects motion trajectory [9]. In addition, we previously clarified that muscle synergy in the sit-to-stand motion is changed due to disturbance of the visual or vestibular input [10]. In this study, we have clarified that visual input affects only the synergy that activates on the transitional period from sit-to-stand motion to posture control, and vestibular input affects the timing of the hip rise.…”

“…For this research, the data of the control condition in our previous study [10] were used. In the measurement experiment, seven healthy people (six males and one female, aged 20-40 years, detailed age was not obtained) participated.…”

“…To understand how to utilize sensory input and feedforward signals to control muscle activity, we aimed to determine which sensory input and feedforward signal are primarily used for controlling muscle activity. Visual, vestibular, and somatosensory inputs are important for posture control [7], but the visual input does not affect sit-to-stand motion when considering sit-to-stand motion itself [10]. Thus, we aim to determine the relationship between muscle activity in the sit-to-stand motion and sensory input from the vestibular and somatosensory input and feedforward signals.…”

Temporal Features of Muscle Synergies in Sit-to-Stand Motion Reflect the Motor Impairment of Post-Stroke Patients

“…First, the start, end, and duration time of temporal patterns were chosen because previous studies found that some post-stroke patients delayed or extended synergy activation, compared with other patients [26]. In addition, our previous study revealed that humans change the duration of muscle synergy to realize adaptive STS motion when their sensory information is impaired [32]. Then, the peak time was selected because our previous study found that the peak time affects STS strategies in healthy adults [24].…”

High-gain observer-based nonlinear control scheme for biomechanical sit to stand movement in the presence of sensory feedback delays

“…Several studies have reported that the CNS regulates human motion and maintains balance by taking inputs from proprioceptors (Muscle Spindles (MS) and Golgi Tendon Organs (GTO)), tactile/somatosensory, visual, and vestibular systems [ 13 – 15 ]. Muscle feedback signals through proprioceptors suffer a delay in transmission to CNS [ 16 , 17 ].…”