Abstract
Humans control balance using different feedback loops involving the vestibular system, the visual system, and proprioception. In this article, we focus on proprioception and explore the contribution of reflexes based on force and length feedback to standing balance. In particular, we address the questions of how much proprioception alone could explain balance control, and whether one modality, force or length feedback, is more important than the other. A sagittal plane neuro-musculoskeletal model was developed with six degrees of freedom and nine muscles in each leg. A controller was designed using proprioceptive reflexes and a dead zone. No feedback control was applied inside the dead zone. Reflexes were active once the center of mass moved outside the dead zone. Controller parameters were found by solving an optimization problem, where effort was minimized while the neuro-musculoskeletal model should remain standing upright on a perturbed platform. The ground was perturbed with random square pulses in the sagittal plane with different amplitudes and durations. The optimization was solved for three controllers: using force and length feedback (base model), using only force feedback, and using only length feedback. Simulations were compared to human data from previous work, where an experiment with the same perturbation signal was performed. The optimized controller yielded a similar posture, since average joint angles were within 5 degrees of the experimental average joint angles. The joint angles of the base model, the length only model, and the force only model correlated weakly (ankle) to moderately with the experimental joint angles. The ankle moment correlated weakly to moderately with the experimental ankle moment, while the hip and knee moment were only weakly correlated, or not at all. The time series of the joint angles showed that the length feedback model was better able to explain the experimental joint angles than the force feedback model. Changes in time delay affected the correlation of the joint angles and joint moments. The objective of effort minimization yielded lower joint moments than in the experiment, suggesting that other objectives are also important in balance control, which cause an increase in effort and thus larger joint moments.
Highlights
Balancing is a complex task, where the aim is to avoid deviations from an upright and unstable position, since these deviations could lead to falls
We address the questions of how much proprioception alone could explain balance control, and whether one modality, force or length feedback, is more important than the other
We aimed to understand the contribution of the proprioceptive system to behavior during perturbed standing
Summary
Balancing is a complex task, where the aim is to avoid deviations from an upright and unstable position, since these deviations could lead to falls. The human is generally modeled as an inverted pendulum to study standing balance (e.g., Van der Kooij et al, 1999; Mergner et al, 2003), since inverted pendulum motion correlates with human motion in standing (Gage et al, 2004). This approach allows for the application of classical control theories to humans (Winter, 1995). A one-link inverted pendulum can be used to study the ankle strategy (Runge et al, 1999), which is active during slower perturbations. A two-link pendulum can be used to study the hip strategy, which is used for faster perturbations (Runge et al, 1999). The dynamics are typically linearized and feedback is applied to the pendulum’s state, with the underlying assumption that the central nervous system is able to recover this information based on the available sensors (Van der Kooij et al, 1999)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
