Bone is constantly being “remodeled,” or removed and replaced by new bone. This process makes the bone more porous, making it more fragile before it regains its strength.

Researchers know that maintaining bone strength while allowing the bone to continue remodeling is challenging because bone’s natural response to daily training is to lower its remodeling rate. It’s all part of the dynamic conditioning process. But the key, one group of Australian scientists said, is providing periods of lower intensity exercise or rest to “give them the chance” to remodel.

Up to 80% of Thoroughbred racehorses have clear evidence of fatigue injuries—small cracks and lesions in the bones due to overloading during training—in the subchondral bone of the distal metacarpus (lower end of the cannon bone), said Chris Whitton, BVSc, PhD, FACVSc, associate professor at the University of Melbourne. Subchondral bone is found below the cartilage and supports the cartilage of the joint surface. So for Whitton and his team, maximizing bone repair in that area in Thoroughbreds is critical.

In his recent study, Whitton and fellow researchers examined cannon bones from 48 Thoroughbred racehorses that had died or been euthanized due to unspecified causes. Some of the horses had been in periods of intense training for at least four weeks at the time of death, while others had been resting with no forced exercise. The scientists compared the physical aspects of the subchondral bone in these horses, looking for injuries, porosity (how porous the bone is), and signs of remodeling