It sounds completely backwards, the idea that you might actually increase health risks by postponing training and competition until a horse is four or older. It goes against the ages-old and widely held belief that you cause damage by initiating work before a horse’s skeleton matures. Yet research conducted from the 1980s through the present day has steadily been debunking the old theories, replacing supposition and circumstantial evidence with hard scientific fact.

In short, the newly understood reality is that done correctly, exercising and even competing a 2-year-old horse could be beneficial by strengthening the horse’s musculoskeletal system and decreasing his long-term risk of injury. We’ll look at the research supporting this theory (most of which relates to racehorses), discuss how the information might apply to other types of riding, and touch on the unknowns that still remain.

The Challenge of Remodeling

The underlying theme that carries through the research done on bone development and exercise is that bone–particularly the cannon bone–must remodel, or change, in order to develop the shape necessary to endure the rigors of racing. According to Rick Arthur, DVM, an American Association of Equine Practitioners (AAEP) past president and a private Southern California racetrack practitioner for 27 years, the cannon bone of a young horse which has not exercised is almost perfectly round (see page 38). But in order to withstand the stresses of racing, the cannon bone must become more elliptical in shape–thicker on the front and inside. The challenge, Arthur adds, is getting the bone to remodel from one shape to the other without tripping the remodeling process over into a clinical problem such as bucked shins or cortical stress fractures (fractures in the outer tubular layer of the bone; see page 37)