Skip to main content
Fig. 2 | Skeletal Muscle

Fig. 2

From: Are mice good models for human neuromuscular disease? Comparing muscle excursions in walking between mice and humans

Fig. 2

The contraction dynamics and force-generating capacity of each muscle-tendon unit was represented by a Hill-type muscle model [35]. (a) The total muscle-tendon length (L MT) was a function of the geometric pose of the musculoskeletal models of mouse hindlimb and human lower limb. The muscle model computes muscle fiber length (L M), muscle pennation angle (α), tendon length (L T), muscle fiber force (F M), and tendon force (F T) based on L MT, muscle activation (a), and the force equilibrium constraints between F M and F T. (b) Tendon was modeled as a non-linear, passive series elastic element, whose mechanical property was defined by the tendon force-strain curve. In this curve, it was assumed that tendon strain (ε T) is 4.9% when muscle fiber developed maximum isometric force (\( {F}_{\mathrm{o}}^{\mathrm{M}} \)). Tendon strain was calculated from the muscle-specific tendon slack length (\( {L}_{\mathrm{s}}^{\mathrm{T}} \)). (c) Muscle fiber was modeled as an active contractile element (CE) in parallel with a passive elastic element (PE). The active force-length curve was scaled by muscle-specific optimal fiber length (\( {L}_{\mathrm{o}}^{\mathrm{M}} \)) and then used to compute active isometric fiber force based on L M and activation (a). The passive force-length curve was also scaled by \( {L}_{\mathrm{o}}^{\mathrm{M}} \) and then used to compute passive fiber force based on L M. (d) The active isometric fiber force was scaled based on fiber velocity (V M) normalized by maximum shortening velocity (\( {V}_{\mathrm{max}}^{\mathrm{M}} \)) of the muscle. Total muscle force was calculated as the sum of active and passive fiber force

Back to article page