Skeletal muscle architecture of the rabbit hindlimb: Functional implications of muscle design

TLDR

The study measured the muscle‑fiber architecture of 29 hindlimb muscles in six rabbits to describe the muscular properties of this cursorial animal. Muscles were classified into hamstrings, quadriceps, dorsiflexors, or plantarflexors to compare architectural properties across groups. Hamstrings and quadriceps, as well as dorsiflexors and plantarflexors, showed significant architectural differences—quadriceps had large pennation angles and low length/mass ratios for force production, while hamstrings had small pennation angles for large excursions, with similar distinctions observed between plantarflexors and dorsiflexors.

Abstract

Abstract The muscle‐fiber architecture of 29 muscles from six rabbits ( Oryctolagus cuniculus ) was measured in order to describe the muscular properties of this cursorial animal, which possesses several specific skeletal adaptations. Several muscles were placed into one of four functional groups: hamstrings, quadriceps, dorsiflexors, or plantarflexors, for statistical comparison of properties between groups. Antagonistic groups (i.e., hamstrings vs. quadriceps or dorsiflexors vs. plantarflexors) demonstrated significant differences in fiber length, fiber length/muscle length ratio, muscle mass, pinnation angle, and number of sarcomeres in series ( P <.02). Discriminant analysis permitted characterization of the “typical” muscle belonging to one of the four groups. The quadriceps were characterized by their large pinnation angles and low fiber length mass ratios, suggesting a design for force production. Conversely, the hamstrings, with small pinnation angles, appeared to be designed to permit large excursions. Similar differences were observed between plantarflexors and dorsiflexors, which have architectural features that suit them for force production and excursion respectively. Although these differences were not absolute, they represented clear morphological distinctions that have functional consequences.