Modeling Skeletal Muscle Stress and Intramuscular Pressure: A Whole Muscle Active–Passive Approach

Abstract

Clinical treatments of skeletal muscle weakness are hindered by a lack of an approach to evaluate individual muscle force. Intramuscular pressure (IMP) has shown a correlation to muscle force in vivo, but patient to patient and muscle to muscle variability results in difficulty of utilizing IMP to estimate muscle force. The goal of this work was to develop a finite element model of whole skeletal muscle that can predict IMP under passive and active conditions to further investigate the mechanisms of IMP variability. A previously validated hypervisco-poroelastic constitutive approach was modified to incorporate muscle activation through an inhomogeneous geometry. Model parameters were optimized to fit model stress to experimental data, and the resulting model fluid pressurization data were utilized for validation. Model fitting was excellent (root-mean-square error or RMSE <1.5 kPa for passive and active conditions), and IMP predictive capability was strong for both passive (RMSE 3.5 mmHg) and active (RMSE 10 mmHg at in vivo lengths) conditions. Additionally, model fluid pressure was affected by length under isometric conditions, as increases in stretch yielded decreases in fluid pressurization following a contraction, resulting from counteracting Poisson effects. Model pressure also varied spatially, with the highest gradients located near aponeuroses. These findings may explain variability of in vivo IMP measurements in the clinic, and thus help reduce this variability in future studies. Further development of this model to include isotonic contractions and muscle weakness would greatly benefit this work.

Anisotropic and viscoelastic tensile mechanical properties of aponeurosis: Experimentation, modeling, and tissue microstructure

“…While determining material properties of aponeurosis can provide quantitative insight into muscle-tendon unit function, they are most useful in developing and employing computational models of the musculoskeletal system. Approaches to model muscle-tendon units range from classical Hill-type models (Ackland et al, 2012), more geometrically complex finite element simulations (Tsui et al, 2004;Wheatley et al, 2018), and larger scale simulations of whole human movement (Rajagopal et al, 2016).…”

Exploring the role of intratendinous pressure in the pathogenesis of tendon pathology: a narrative review and conceptual framework

“…Although a direct analysis of IDP has not yet been carried out, a positive correlation between fluid pressure and passive strain has already been demonstrated in nerves and muscles. [93][94][95][96] For example, intraneural pressure in the sciatic nerve increases from 8 mm Hg to 56 mm Hg during a straight leg raise. 95 Theoretical and experimental studies have also shown that fluid pressure increases strongly when hydraulic permeability of the ECM decreases, as this is associated with a higher resistance to fluid flow.…”

The effects of gravity and compression on interstitial fluid transport in the lower limb

“…Typically, the tissue is modeled as a saturated poroelastic material that is divided into solid and fluid subvolumes. At the local scale (about 1 cm) poroelastic methods have been employed in the contexts of solid tumors 27 – 33 , injection sites 34 – 39 , under indentation probes 40 – 42 , near the edge of a compression wraps and in normal tissues 43 – 47 . The local models often include capillary permeability and lymphatic clearance, but over such relatively short distances, gravity has little opportunity to build significant hydrostatic pressures.…”