Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Thursday Speaker Abstracts

AN EXPERIMENTAL APPROACH TO MANIPULATE THE MULTI-SCALE COMPONENTS OF WHOLE-BODY MOVEMENT THAT INFLUENCE SINGLE MUSCLE FIBER WORK AND POWER OUTPUT David C Lin 1,2 ; Bertrand C.W. Tanner 1,2 ; 1 Washington State University, Integrative Physiology and Neuroscience, Pullman, WA, USA 2 Washington State University, Voiland School of Chemical Engineering and Bioengineering, Pullman, WA, USA Locomotion includes coupling between muscles, tendons, bones, and joints, which intrinsically form a multi-scale mechanical feedback system. Namely, the forces and length changes that occur in a muscle fiber are influenced by muscle architecture, mechanical characteristics of the attached tendon, musculoskeletal geometry, and inertias of the limbs and body. To probe how muscle performance is affected by these elements, it is necessary to manipulate the properties of these elements to better understand system coupling. While this manipulation is possible in computational models, experimentally manipulating these elements is difficult, especially as the scale becomes larger and the system contains more elements. To address this challenge, we have developed a virtual mechanical load environment for single skeletal muscle fibers based on the concept of mechanical impedance and implemented by force-feedback. Within this environment, we can manipulate crossbridge mechanisms via solution-based methods, as well as muscle architecture, tendon, and inertial properties. These manipulations can be either parametric (e.g., increasing tendon compliance) or introduce nonlinear behavior (e.g., including the “toe” region of tendon). Our initial study addressed how tendon compliance influences muscle power and work output as a fiber is activated from rest (relaxed conditions). We tested compliance values spanning a 50-fold change, while activating chemically-skinned fibers from a rat medial gastrocnemius. Power output from the fiber increased nonlinearly with increases in tendon compliance. Interestingly, there was not a large change in muscle force throughout the movement for the different compliances, implying force-velocity effects were not prominent, potentially due to the activation-driven force increase from rest. Future studies will examine how the toe region of tendon and rotation of fibers within a whole muscle (i.e., changes in pennation angle) influence muscle power generation.

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