Nonlinear response of human trunk musculature explains neuromuscular stabilization mechanisms in sitting posture

Abstract

Objective: Determining the roles of underlying mechanisms involved in stabilizing the human trunk during sitting is a fundamental challenge in human motor control. However, distinguishing their roles requires understanding their complex interrelations and describing them with physiologically meaningful neuromechanical parameters. The literature has shown that such mechanistic understanding contributes to diagnosing and improving impaired balance as well as developing assistive technologies for restoring trunk stability. This study aimed to provide a comprehensive characterization of the underlying neuromuscular stabilization mechanisms involved in human sitting. Approach: This study characterized passive and active stabilization mechanisms involved in seated stability by identifying a nonlinear neuromechanical physiologically-meaningful model in ten able-bodied individuals during perturbed sitting via an adaptive unscented Kalman filter to account for the nonlinear time-varying process and measurement noises. Main results: We observed that the passive mechanism provided instant resistance against gravitational disturbances, whereas the active mechanism provided delayed complementary phasic response against external disturbances by activating appropriate trunk muscles while showing non-isometric behavior. The model predicted the trunk sway behavior during perturbed sitting with high accuracy and correlation (average: 0.0007 [rad2] and 86.77%). This allows a better mechanistic understanding of the roles of passive and active stabilization mechanisms involved in sitting. Significance: Our characterization approach accounts for the inherently nonlinear behavior of the neuromuscular mechanisms and physiological uncertainties, while allowing for real-time tracking and correction of parameters’ variations due to external disturbances and muscle fatigue. The outcome of our research, for the first time, (1) allows a better mechanistic understanding of the roles of passive and active stabilization mechanisms involved in sitting; (2) enables objective evaluation and targeted rehabilitative interventions for impaired balance; facilitate bio-inspired designs of assistive technologies, and (3) opens new horizons in mathematical identification of neuromechanical mechanisms employed in the stable control of human body postures and motions.

Nonlinear neural control using feedback linearization explains task goals of central nervous system for trunk stability in sitting posture

“…Second, their model neglects the sensory time delay, and the extent of contributions of passive control to postural stability was neglected. As presented by previous studies [22,23,46], passive control primary depends on the angular position and velocity and has a significant contribution towards postural control. Therefore, their interpretation regarding the role of the velocity information for the neural feedback may have been affected by not separating the passive and active control mechanisms, since the passive control mechanism depends on the angular position and velocity.…”

“…Previous studies have proposed a nonlinear neuromechanical model of seated stability [46]. The nonlinear neuromechanical dynamics of the seated stability was modeled, as illustrated in figure 2.…”

“…The use of UKF, in the previous study, allowed us to observe the state vector (x) of the nonlinear system based on the measurement of the trunk sway angle (y) and the total motor command (u) [46]. In the present study, to characterize the task goals of the neural control, we assumed that:…”

Kinesiological models of the neuromuscular system readaptation in mature women after prolonged hypokinesia

“…This process occurs due to an increase in the number of active mobile muscle units [11]. However, increasing the level of intra-muscular and inter-muscular coordination leads to a significant increase in energy consumption and the need to increase the functional capabilities of the body [16,19].…”

“…Solving this issue requires an integrated approach due to the combination of modern research in power fitness, sports physiology, biochemistry of motor activity, diagnostics of body systems, dynamic anatomy [2,10,15]. A comprehensive approach to the process of modeling the effective activities for the neuromuscular system readaptation requires substantiating the correspondence of the external stimulus to the initial level of the body adaptive reserves [16,17]. Using innovative complexes of physical exercises with different kinematics, methods of load correction depending on the features of adaptive and compensatory reactions to the stimulus, assessment of the functional state and the neuromuscular system state are the basis for modeling.…”