Functional anatomy and muscle moment arms of the pelvic limb of an elite sprinting athlete: the racing greyhound (Canis familiaris)

Abstract

We provide quantitative anatomical data on the muscle-tendon architecture and geometry of the pelvic limb of an elite sprint athlete, the racing greyhound. Specifically, muscle masses, muscle lengths, fascicle lengths, pennation angles and muscle moment arms were measured. Maximum isometric force and power of muscles, the maximum muscle torque at joints and tendon stress and strain were estimated. We compare data with that published for a generalized breed of canid, and other cursorial mammals such as the horse and hare. The pelvic limb of the racing greyhound had a relatively large volume of hip extensor muscle, which is likely to be required for power production. Per unit body mass, some pelvic limb muscles were relatively larger than those in less specialized canines, and many hip extensor muscles had longer fascicle lengths. It was estimated that substantial extensor moments could be created about the tarsus and hip of the greyhound allowing high power output and potential for rapid acceleration. The racing greyhound hence possesses substantial specializations for enhanced sprint performance.

Fig. 1

Photograph depicting the experimental set-up for obtaining muscle moment arms. See text for full method.

Fig. 2

(A) Superficial musculature of the greyhound pelvic limb. (B) Proximal musculature of the greyhound pelvic limb (M. biceps femoris removed). (C) Deep musculature of the proximal pelvic limb and distal limb musculature of the racing greyhound. Ms. biceps femoris, tensor fascia lata, sartorius, vastus lateralis, gluteus superficialis, gluteus medius and gluteus profundus have been removed.

Fig. 3

Muscle mass of individual pelvic limb muscles scaled to total body mass. Pale bars represent racing greyhound data from this study (mean ± SD), whilst dark bars show data from Shahar & Milgrim (2001) for a mixed-breed dog.

Fig. 4

Moment arm curves for individual pelvic limb muscles at (A) the hip, (B) the stifle and (C) the tarsus joints. Moment arms are scaled to limb segment lengths, as described in the text. Segment lengths can be found in Table 4.3. Positive values for moment arms indicate muscles that act to flex a joint, whereas negative values indicate joint extensors. Arrows indicate the functional range of joint motion during stance in galloping greyhounds (Williams, unpublished data).

Fig. 6

(A) Schematic representation of the effect of increased muscle volume and Architectural Index on muscle power output. The star represents the position of the hypothetical muscle on the plot. Arrows show how the position of the star is likely to move towards that of powerful muscles (pale blue region) with increased muscle volume and Architectural Index. (B) F_max against fascicle length for individual racing greyhound pelvic limb muscles.

Fig. 5

Architectural Index (calculated as described in the text) for individual pelvic limb muscles of greyhounds (pale bars) and a mixed-breed dog (dark bars; Shahar & Milgrim, 2001).

Fig. 7

Tendon length change: Muscle fascicle length (TLC : MFL) ratio for selected pelvic limb muscle tendon units. Tendon length change is based on that at F_max.

Fig. 9

Muscle moment arm length versus muscle fascicle length. This ratio gives information regarding the individual roles of muscles during movement. Abbreviations are given in Table 1. Blue symbols show muscles crossing the hip joint, green crossing the stifle, and red crossing the tarsus.

Fig. 8

Total maximum isometric joint torque for flexor (pale) and extensor (dark) muscle groups at each joint within the racing greyhound pelvic limb.