Equine Muscle Types Match Breeds’ Usual Work

All horses have muscle tissue made up of both slow-twitch and fast-twitch fibers. Slow-twitch fibers are used for slower work such as easy trail riding and some phases of endurance racing, and fast-twitch fibers are activated for sprint races and speed work such as barrel racing. While every horse has fibers of both types, it is not surprising that different breeds have characteristic ratios that allow them to excel at particular types of performance.

Selective breeding over many centuries has produced horse breeds that are well-equipped for the performance they are usually asked to do. Thus, today’s Thoroughbreds have an average of 80 to 90% fast-twitch muscle fibers, while Arabian and Standardbred horses are close to this level with about 75% fast-twitch fibers. In contrast, horses of draft breeding have a much lower percentage of these fibers and are better suited to periods of slower work.