A Comprehensive Mechanistic Model of Muscle Force and Impedance Across Length Scales

Khái niệm cốt lõi

The VEXAT model can accurately capture the force response of muscle to both small and large length perturbations, as well as reproduce the force-velocity and force-length relations of muscle.

Tóm tắt

The paper presents the viscoelastic-crossbridge active-titin (VEXAT) model, a comprehensive mechanistic model of muscle force and impedance. The key highlights and insights are:

The VEXAT model can replicate the response of muscle to both small and large length perturbations, which is important for capturing the mechanics of everyday movements.

For small perturbations, the model's active response is well captured by a linear-time-invariant (LTI) system with a stiff spring in parallel with a light damper, consistent with experimental observations.

For larger stretches, the model includes a compliant spring (titin) that can fix its end when activated, allowing the muscle to develop high forces during active lengthening beyond actin-myosin overlap.

The VEXAT model more accurately captures the impedance of biological muscle and its responses to long active stretches compared to a popular Hill-type muscle model, while still reproducing the force-velocity and force-length relations.

The model is formulated to have a small number of states, making it well-suited for large-scale simulations of musculoskeletal systems.

The model parameters are estimated from the literature and can be used as initial values when modeling other mammalian musculotendon units.

Thống kê

"The stiffness that best captures the response of muscle to the small perturbations of Kirsch et al. [5] is far greater than the stiffness that best captures the response of muscle to large perturbations [7], [8]."
"Titin has proven to be a complex filament, varying in composition and geometry between different muscle types [28], [29], widely between species [30], and can apply activation dependent forces to actin [31]."
"Titin's passive-force-length properties scale from single molecules to myofibrils [57], [58]"

Trích dẫn

"The force response of muscle is not uniform, but varies with both the length and time of perturbation."
"Since everyday movements are often accompanied by both large and small kinematic perturbations, it is important to accurately capture these two processes."
"Titin has proven to be a complex filament, varying in composition and geometry between different muscle types [28], [29], widely between species [30], and can apply activation dependent forces to actin [31]."

Thông tin chi tiết chính được chắt lọc từ

A three filament mechanistic model of musculotendon force and impedance

by Millard,M., ... lúc www.biorxiv.org 03-28-2023

https://www.biorxiv.org/content/10.1101/2023.03.27.534347v5

Yêu cầu sâu hơn

How could the VEXAT model be extended to capture other complex muscle behaviors, such as history-dependent effects like residual force enhancement

To extend the VEXAT model to capture history-dependent effects like residual force enhancement (RFE), we can incorporate additional elements or mechanisms that account for these phenomena. One approach could be to introduce a memory component into the model that retains information about past activations and length changes. This memory element could influence the behavior of the viscoelastic crossbridge and active titin elements, allowing the model to exhibit history-dependent effects such as RFE. By incorporating feedback loops or state variables that store information about previous activations and length changes, the model can dynamically adjust its response based on past interactions, mimicking the behavior of muscle with memory-dependent properties like RFE.

What are the potential limitations of the lumped-parameter approach used in the VEXAT model, and how could a more detailed, multi-scale model improve the accuracy of muscle force predictions

The lumped-parameter approach used in the VEXAT model simplifies the complex structure and behavior of muscle into a few key elements, which may limit its ability to capture all aspects of muscle physiology accurately. One potential limitation is the assumption of uniform properties across the muscle, neglecting the heterogeneous nature of muscle tissue. A more detailed, multi-scale model could improve accuracy by incorporating variations in muscle architecture, fiber types, and activation patterns. By including finer details such as individual sarcomeres, motor unit recruitment, and fiber pennation angles, a multi-scale model can provide a more comprehensive understanding of muscle behavior. Additionally, integrating biophysical properties at the molecular level, such as cross-bridge kinetics and titin isoform variations, can enhance the model's predictive capabilities and realism.

Given the importance of muscle impedance for motor control, how could the VEXAT model be integrated into computational neuroscience frameworks to study the neural control of movement

Integrating the VEXAT model into computational neuroscience frameworks for studying the neural control of movement offers valuable insights into how muscle impedance influences motor behavior. By linking the model with neural control algorithms, researchers can simulate realistic interactions between the central nervous system and musculoskeletal system during movement tasks. This integration can help investigate how neural signals modulate muscle activation, stiffness, and damping properties to achieve desired movements. Furthermore, coupling the VEXAT model with neural network models can elucidate how motor commands are translated into muscle forces and how sensory feedback influences motor control strategies. Overall, incorporating the VEXAT model into computational neuroscience frameworks enables a more comprehensive understanding of the complex interplay between neural circuits and musculoskeletal dynamics in motor control.