Functional specialisation of pelvic limb anatomy in horses
As supplementation to: The role of thoracic limb muscles in equine locomotion, this study provides equal information on the anatomy and biomechanics of the major muscle and tendon units of the pelvic limb. In contrast to thoracic limb muscles, proximal pelvic limb muscle were larger and had shorter fascicles. The anatomy of the distal limb was similar in all limbs. However the distal hind limb revealed to have an additional muscle: the flexor digitorum lateralis (laterally to the deep digital flexor). The shape is alike superficial digital flexors of the fore- and hindlimb, suggesting equal function.
The mono-articular hip extensor gluteus medius and the bi-articular vertebral head of biceps femoris were by far the largest muscles. They form a group of muscles together with semimembranosus, semitendinosus and the adductors, featured by large volumes and long fascicles. Typical qualities for muscles specialized for doing work and generating high power. Acceleratory impulses are greatest in the pelvic limb, thus relatively powerful hip extensors might expected.
The limb protractors: psoas major, psoas minor, iliacus and rectus femoris were not large and therefore are not capable of generating either large forces or powerful contractions. Protraction starts at the end of stance by active shortening of the hip flexor muscles but maintained through swing via passive recoil of elastic structures. This system is likely enough for limb protraction, because the protracting limb need only overcome: air resistance, its own weight and inertia.
If you would like to know more about the specific muscle and tendon properties of the pelvic limb, read the full article: Full-text
R. Payne et al., Equine pelvic limb anatomy, Anat. (2005) 206, pp 557–574. All rights reserved to: Anatomical Society of Great Britain and Ireland 2005. Click here for the Pubmed summary