Thoroughbreds: Natural Born Runners

As Secretariat approached the turn for home in the 1973 Belmont Stakes, picking up speed and literally leaving his rivals in the dust, race announcer Chic Anderson uttered one of the most memorable and marvelously accurate lines in sports history: “He is moving like a tremendous machine!”

And indeed, he was. Here was a perfectly built, finely tuned racehorse, with all components working in mechanical harmony. The result is as dominant a performance as you will ever see.

We all know thoroughbreds are specially bred for speed and stamina, but what exactly makes them biologically unique? What's under the hood?

Let’s explore five key running speed components that give thoroughbreds the ability to “convert air into blazing speed.” 

1. Fast and slow twitch muscles. Horses have two general types of muscle fibers: type 1, or slow-twitch, and type 2, fast-twitch. Most thoroughbreds have a much higher percentage of fast-twitch fibers, which provide the raw power and speed needed to propel them forward at high speeds. However, horses bred and conditioned to run longer distances have a good balance of each, giving them better MPG than, say, a Quarter Horse or barrel racer. 

2. Spleen. When the going gets tough, the spleen kicks in. A thoroughbred's spleen can churn out as much as an additional 12 liters of blood during exercise. More blood means more oxygen to fuel the action.

3. Big Hearts. Simply put: the bigger the heart, the more blood that gets pumped to the muscles. It’s not uncommon for some thoroughbreds to have a heart twice as big as the average equine. It’s referred to as the “large heart gene”, and is carried via the x-chromosome. Secretariat famously possessed the gene, and his heart is estimated to have weighed over 20 pounds.

4. Latherin. Ah, the scent of a horse. As flight animals, horses must sweat in order to dissipate heat when exercising, much like humans. Unlike humans, equine sweat is a protein-based, detergent-like fluid that facilitates the cooling process. It is also produced by salivary glands, giving off that welcoming “foaming at the mouth” vibe.

5. Respiratory Tract. Air intake fuels this whole process. The upper respiratory tract is one of the first things you evaluate when considering a thoroughbred’s potential (or any sport horse, for that matter), and is constantly monitored throughout a career. If a racehorse has a narrow tract or is prone to inflammation, they won’t be able to take in enough air to adequately power the engine.