This is an excerpt from Run Healthy by Emmi Aguillard,Jonathan Cane & Allison L. Goldstein.
The composition of tendons and ligaments is what makes injury to them so frustrating. As mentioned earlier, adequate blood flow is how the body heals and repairs damaged tissues, so a part of the body that has less vascularization (blood flow) will take longer to heal. Because tendons and ligaments have a lesser supply of blood vessels and vascularization than muscles do, healing and rehabilitating tendon or ligament injuries takes longer.
When injury or damage to a tendon or ligament occurs, the parallel collagen fibers tear, and scar tissue forms. As the body repairs these fibers, due to the scar tissue, they are no longer aligned in the strong, resilient, parallel form they once were. Consequently, appropriate rehabilitation requires specific exercises to promote blood flow and realign the fibers to rebuild resilience and prevent reinjury.
Knowing the correct way to rehabilitate a tendon or ligament injury is critical. You may have been frustrated when, after taking two weeks off from running due to Achilles pain, your pain came right back. Or maybe you have experienced tendinitis that seemed to feel better after you ran. The reason these things can happen is that, somewhat counterintuitively (especially if you’ve had muscle or bone injuries in the past that required complete rest), incorporating exercises, modalities, and strategies that increase blood flow to the damaged region is the most effective way to help the body heal. An immobilized tendon or ligament will not receive adequate blood flow to heal; therefore, rest alone is rarely the answer for this type of injury. In order to facilitate healing in a tendon or ligament, exercises that promote increased blood flow to the region while loading the tissue submaximally (i.e., with less force than what caused the injury but with enough force to help the tissue to heal) is critical. This is also why these injuries can be so tough to overcome; the injured tendon or ligament requires enough stress to stimulate healing, but too much can cause an increase in inflammation, which is counterproductive. This line is very fine. We are going to get more specific in upcoming chapters about how to do this for a few of the most common running injuries, but these same principles apply to the entire body.