An equine athlete uses the pelvis and sacroiliac (SI) joint in many different fashions: A rope horse uses the pelvis to rapidly accelerate and decelerate, a Standardbred races at high speed at a constrained gait, and a dressage horse exercises with repetitive and isometric control of his haunches. Furthermore, a vaulting horse is constrained to a circle, but he must provide stability of his back, a jumping horse requires large propulsive forces to use his rear legs to launch over a jump, and a Thoroughbred racehorse at a high-speed run experiences lots of forces through his pelvis, while a cutting horse needs agility and fine-tuned proprioceptive control and balance during rapid hind limb movements. At the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif., Kevin Haussler, DVM, DC, PhD, an assistant professor at Colorado State University, discussed the relationship between motions at the SI joint to deformation of the pelvis in the exercising horse.