Identification of Autogenic Force Feedback Responses In Elbow Flexor Muscle Group

Although previous studies have elucidated the role of position feedback in the regulation of movement, the specific contribution of Golgi tendon organs (GTO) in force feedback, especially in stabilizing voluntary limb movements, has remained theoretical due to limitations in experimental techniques. This study aims to establish force feedback regulation mediated by GTO afferent signals in two phases. The first phase of this study consisted of simulations using a neuromusculoskeletal model of the monoarticular elbow flexor (MEF) muscle group, assess the impact of force feedback in maintaining steady state interaction forces against variable environmental stiffness. Three models were trained to accurately reach an interaction force of 40N, 50N and 60N respectively, using a fixed stiffness level. Next, the environment stiffness was switched between untrained levels for open loop (OL) and closed loop (CL) variants of the same model. Results showed that compared to OL, CL showed decreased force deviations by 10.43%, 12.11% and 13.02% for each of the models. Most importantly, it is also observed that in the absence of force feedback, environment stiffness is found to have an effect on the interaction force. In the second phase, human subjects were engaged in experiments utilizing an instrumented elbow exoskeleton that applied loads to the MEF muscle group, closely mimicking the simulation conditions. The experiments consisted of reference, blind and catch trial types, and 3 stiffness levels. Subjects were first trained to reach for a predetermined target force. During catch trials, stiffness levels were randomized between reaches. Responses obtained from these experiments showed that subjects were able to regulate forces with no significant effects of trial type or stiffness level. Since experimental results align closely with that of closed loop model simulations, the presence of force feedback mechanisms mediated by GTO within the human neuromuscular system is established. This study not only unveils the critical involvement of GTO in force feedback but also emphasizes the importance of understanding these mechanisms for developing advanced neuroprosthetics and rehabilitation strategies, shedding light on the intricate interplay between sensory inputs and motor responses in human proprioception.