Functional specialisation of the pelvic limb of the hare (Lepus europeus)

Abstract

We provide quantitative anatomical data on the muscle-tendon architecture of the hare pelvic limb (specifically muscle mass, fascicle length, pennation angle, tendon mass and length). In addition, moment arms of major pelvic limb muscles were measured. Maximum isometric force and power of muscles, the moment of force about a joint, and tendon stress and strain were estimated. Data are compared with published data for other cursorial mammals such as the horse and dog, and a non-specialised Lagamorph, the rabbit. The pelvic limb of the hare was found to contain substantial amounts of hip extensor and adductor/abductor muscle volume, which is likely to be required for power production and stability during rapid turning. A proximal to distal reduction in muscle volume and fascicle length was also observed, as is the case in other cursorial quadrupeds, along with a reduction in distal limb mass via the replacement of muscle volume by long distal limb tendons, capable of storing large amounts of elastic energy. The majority of hare pelvic limb muscle moment arms varied with joint position, giving the hare the capacity to vary muscle function with limb posture and presumably different locomotor activities.

Fig. 1

Schematic line drawing showing superficial and underlying musculature of the lateral aspect of the hare pelvic limb.

Fig. 2

Functional distribution of muscle mass within the pelvic limb for hares (pale blue bars), rabbits (dark) and horses (white). Rabbit data are from Lieber & Blevins (1989). Note that gluteal, psoas, IL and SRT muscles are missing from this study; see text. Horse data are from Payne et al. (2005). Hare data are means ± SD (n = 8).

Fig. 3

Architectural index (AI) for hare pelvic limb muscles. Abbreviations are given in Table 1. Values are means ± SD (n = 8).

Fig. 4

Mean moment arms (scaled to femur or tibia length, see Methods described in text; mean femur length 115 mm, mean tibia length 137 mm). Lengths for individual hares are given in Table 4 for selected pelvic limb muscles across the full range of physiologically relevant joint positions. (a) Superficial muscles acting at the hip joint; (b) deep muscles acting at the hip joint; (c) muscles acting at the knee joint; (d) muscles acting at the ankle joint.

Fig. 5

Semitendinosis muscle (indicated by arrow) within bisected adductor muscle belly. Values on scale are in cm.

Fig. 6

Estimated muscle F_max against fascicle length for hare pelvic limb muscles. Values are means (n = 8). Solid points represent distal limb muscles, whilst proximal muscles are represented by open circles. Abbreviations are given in Table 1.

Fig. 7

Ratio of tendon elongation (estimated length change elicited at muscle maximum isometric force) to muscle fascicle length (TLC:MFL) for selected pelvic limb tendons in the hare. Data are means ± SD (n = 8).