Fig 1.
Hill-type muscle model and associated muscle properties.
The muscle model [28, 29] for which the parameters are determined in this study consists of a contractile component (CC), a serial elastic component (SEC) and a parallel elastic component (PEC). Muscle components and associated muscle properties (force-velocity relation, force-length relation, activation-time relation, force-elongation relation of SEC and PEC) are marked with the same background color. Corresponding model parameters are explained in section 2.3.
Fig 2.
Schematic of the rabbit calf muscles.
(A) Medial view of the left pelvic limb and the calf muscles whose dynamic muscle properties and architecture have been determined (GAS, PLA, SOL). The grey dashed line marks the transversal cross-section of the limb shown in (B). For the grey muscles (FDL, EDL, and TA), only dynamic muscle properties were determined (see Supporting Information, S1 Text). White muscles (**peronaei muscles, * M. extensor hallucis longus) were not examined. The axes are shown for orientation.
Table 1.
Specifications of observed muscles.
Fig 3.
Muscle properties of GAS, PLA, and SOL.
The black curves indicate mean values, whereas the grey areas depict the standard deviations. First row: force–length (fl) relation. Fim is the maximum isometric muscle force, lCC and lCCopt are the length and the optimal length of the contractile component, respectively. To avoid muscle damage, the muscles were lengthened until passive forces reached about 0.2 Fim (marked with a white circle). Second row: force–velocity (fv) relation. vCCmax is the maximal shortening velocity of the contractile component. Third row: Force–strain relation of the series elastic component (SEC). ΔlSEC and lSEC0 are the length change and the slack length of the series elastic component, respectively. Last row: Force–strain relation of the parallel elastic component (PEC). ΔlPEC and lPEC0 are the length change and the slack length of the parallel elastic component, respectively.
Table 2.
Muscle parameters of GAS, PLA, and SOL.
Fig 4.
Force enhancement (FE) and force depression (FD) experiments.
Typical experiments are shown for one GAS (m = 14.8 g), SOL (m = 3.3 g), and PLA (m = 7.5 g), respectively. Exemplary isokinetic ramps are depicted for GAS in the top row; numbers without units indicate velocity in mean fascicle lengths per second. FE (difference between black triangles) and FD (difference between white triangles) are the force difference between ramp experiment (black) and isometric reference contraction (grey) determined 500ms (GAS, PLA) and 1300ms (SOL) after the end of the ramp, shown exemplarily for the slowest (0.35 lfm/s) ramp.
Fig 5.
Muscle architectures of GAS, PLA, and SOL of R1 left pelvic limb.
Muscle fascicles of GAS medialis and lateralis are shown in light red and yellow, respectively. The proximodistal axis corresponds to the mean force axis of the calf muscles, running from mean muscle origin at the humerus to the insertion at the calcaneus. The corresponding 3D data of the muscle fascicles are provided in the Supporting Information (S2–S4 Datasets).
Table 3.
Muscle architecture of GAS, PLA, and SOL.