Bone was once considered an inert material with its structure defined by genetics. But it turns out there’s a lot more at work, explained Larry Bramlage, DVM, MS, Dipl. ACVS: “Selective breeding dictates the initial skeleton, but adaptive training in response to exercise modifies it further.” He and other racehorse surgeons are striving to better understand the balance between tolerable and excessive damage—the adaptive kind that occurs naturally and the type that sidelines animals or ends their careers.
During his presentation at the 2013 American Association of Equine Practitioners’ Convention, held Dec. 7-11 in Nashville, Tenn., Bramlage, of Rood & Riddle Equine Hospital, in Lexington, Ky., explained that bone is the only tissue capable of entirely reconstituting itself. With this capacity to change, he noted, there are several ways long bones strengthen themselves in response to training, including modeling and remodeling. Modeling is the process in which bone adds to itself, both inside and out, while remodeling is how existing bone tissue alters itself.
Bramlage started by describing the dynamic nature of bone activity on a cellular level. Two types of bone cells are involved in bone modeling and remodeling: osteoblasts and osteoclasts. Osteoblasts become trapped in the bone and become osteocytes, which are key to sensing biomechanical loads on the skeleton during exercise and directing bone tissue response accordingly. As they detect mechanical loads, they prompt additions to (formation) or reductions in (dissolution) bone mass, to achieve correct bone density for current athletic demands. Osteoclasts then tunnel through and cut canals into the bone, with osteoblasts following to make new bone.