Three-Dimensional Muscle Architecture and Comprehensive Dynamic Properties of Rabbit Gastrocnemius, Plantaris and Soleus: Input for Simulation Studies

Abstract

The vastly increasing number of neuro-muscular simulation studies (with increasing numbers of muscles used per simulation) is in sharp contrast to a narrow database of necessary muscle parameters. Simulation results depend heavily on rough parameter estimates often obtained by scaling of one muscle parameter set. However, in vivo muscles differ in their individual properties and architecture. Here we provide a comprehensive dataset of dynamic (n = 6 per muscle) and geometric (three-dimensional architecture, n = 3 per muscle) muscle properties of the rabbit calf muscles gastrocnemius, plantaris, and soleus. For completeness we provide the dynamic muscle properties for further important shank muscles (flexor digitorum longus, extensor digitorum longus, and tibialis anterior; n = 1 per muscle). Maximum shortening velocity (normalized to optimal fiber length) of the gastrocnemius is about twice that of soleus, while plantaris showed an intermediate value. The force-velocity relation is similar for gastrocnemius and plantaris but is much more bent for the soleus. Although the muscles vary greatly in their three-dimensional architecture their mean pennation angle and normalized force-length relationships are almost similar. Forces of the muscles were enhanced in the isometric phase following stretching and were depressed following shortening compared to the corresponding isometric forces. While the enhancement was independent of the ramp velocity, the depression was inversely related to the ramp velocity. The lowest effect strength for soleus supports the idea that these effects adapt to muscle function. The careful acquisition of typical dynamical parameters (e.g. force-length and force-velocity relations, force elongation relations of passive components), enhancement and depression effects, and 3D muscle architecture of calf muscles provides valuable comprehensive datasets for e.g. simulations with neuro-muscular models, development of more realistic muscle models, or simulation of muscle packages.

The active force–length relationship is invisible during extensive eccentric contractions in skinned skeletal muscle fibres

“…Many studies have reported a linear rise in tension for moderate muscle lengthening that is independent of contraction speed for whole muscles [22][23][24], across muscle fibre bundles [25,26], down to intact single fibres [18]. These findings agree with the idea of a passive, spring-like contribution of, for example, titin to total muscle force.…”

Intermuscular pressure between synergistic muscles correlates with muscle force

“…By this filter selection, the signal noise was effectively reduced without changing the characteristics of the trajectories. In accordance with previous findings, we assumed the ascending limb of the force-length relationship to be linear (Blix, 1894;Gordon et al, 1966;Siebert et al, 2015). Therefore, least-squares linear regressions were used to determine the relationships between muscle length, isometric force, and intermuscular pressure in the ascending limb.…”

“…The study was conducted on the basis of well-established methods and procedures to determine muscle properties and deformations that have already been described in detail (Böl et al, 2013(Böl et al, , 2015Siebert et al, 2015).…”

“…This length was defined as zero muscle l opt , muscle length at F im ; l reg and l max are the maximum muscle length for regression analyses and muscle length at the maximum intermuscular pressure, respectively; F im , maximum isometric force. Maximum muscle stress was calculated using muscle mass, optimal fibre length and muscle density of 1.056 g cm −3 (Mendez and Keys, 1960;Siebert et al, 2015).…”

“…1B) of the TA and the absence of overlying muscles and, thus, transversal compression. Moreover, the lower pennation angles of TA (approximately 3 deg; Lieber and Blevins, 1989) compared with that of the calf muscles (approximately 15 deg; Siebert et al, 2015) result in lower transversal forces, which might contribute to lower IaMP.…”