With the recent Athens Olympics as our inspiration, we might all be pondering what it takes to go “faster, higher, and stronger.” Whether you’re a human, a hamster, or a horse, the answer, at least in part, is muscle fibers–each of which holds within it a certain potential for athletic performance.

When muscle fibers work together, they can provide the impetus for explosive forward or upward motion, steady exertion over long periods, or more commonly some combination of all of these types of movement. As we unlock the secrets of muscle structure, we begin to see how different types of fibers function, how much a horse’s performance might be predetermined by the distribution of muscle fibers he’s born with, and even how we might be able to influence the proportions of various muscle fibers, and their efficiency, through training.

Muscle Fiber Basics

According to Ray Geor, BVSc, PhD, Dipl. ACVIM, an associate professor in the Biomedical Sciences Department at the Ontario Veterinary College in the University of Guelph, 90% of a skeletal muscle is made up of muscle fibers (sometimes called myofibrils). These are elongated cells with tapered ends that are bundled parallel to each other. The rest of the muscle composition is largely nerves and capillaries, which keep the cells supplied with nutrients