Front Matter

Chapter 3 Musculoskeletal Structure and Physiology 53

However, this fiber type difference is of low
functional significance as the metabolic
capability of the differing type II fibers is not
dramatically different. In general, canine
skeletal muscle has high mitochondrial density
and oxidative capacity and is adapted to endur­
ance activities (Wakshlag et al., 2004).
Overall muscling and fiber type differences
have been observed between breeds of dogs;
these are exemplified by the observed
differences between Greyhounds and other
breeds. The Greyhound has approximately 15%

more muscle mass, and higher overall muscle‐

to‐bone ratios than other breeds (Gunn, 1978b).

Greyhounds also have unique fiber type

distributions, with approximately 75–100%

type II fibers in the semitendinosus while other

breeds typically have fewer than 50% type II

fibers (Gunn, 1978a). These differences explain

why Greyhounds are sprinters unlike the

majority of other breeds. Little work has

been  performed across breeds to examine the

energetics of muscle and how training affects

performance.

Z

Actin filament Myosin filament

Myosin pulls actin inward

Contracted

Relaxed

I

Z

I

H

A

Figure 3.7 Contraction of skeletal muscle occurs due to ATP‐dependent conformational changes of the globular
heads of myosin proteins that cause myosin to slide along adjacent actin filaments. Source: Used with permission
from Hand et al., 2010.