Circulation especially in the horses legs is aided by movement. Massage is helpfully in many different types of injury rehabilitation's, not just muscular. Once your horse has been stalled with a muscle or tendon injury, the waiting begins. The increased compensation shows up through out the horses body but primarily in the diagonal shoulder, i.e. left shoulder. Blood is the life stream literally for the healing process.
Massage provides the manual kneading that helps maintain an adequate blood flow.
Once the acute stage, the first 72 hours typically, has passed, gentle massage above and below the injury site once again can increase and maintain healing circulation in your stalled horse. Work done on an injured horse that is on Bute or any other pain medication isn't recommended. MUST first be cleared by your Veterinarian. Finally, when a body part hurts, we tend not to move it, not moving it decreases the pain but also decreases the blood flow and makes the area stiff. Stiffness can lead to more pain and the cycle of pain begins.