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Bone stress injuries occur in distance runners when bone is unable to adapt at a rate that meets the demands of the load being applied. The most common cause of bone stress injuries is training error related to intensity and/or volume. This includes sudden increases in training load, or cumulative load when adequate rest periods are not implemented to allow for adaptation. When a bone remodels effectively, bone cells called osteoclasts remove damaged regions so that bone-forming osteoblasts can lay down new bone. A bout of loading (running) leads to microdamage so that the bone can adapt and become stronger. But, repetitive loads that surpass the body’s ability to recover can lead to weakened bones that are at greater risk for injury. Distance running is not the most advantageous form of bone loading because of its repetitive nature. After just a few minutes of running, bone cells lose mechanosensitivity, meaning they stop responding or taking the stimulus as a sign to remodel. So although running, and other high impact activities, are vital for stimulating bone growth and adaptation, the cumulative stress of distance running does not always serve to strengthen bones. It has been shown that BSIs begin appearing ~3-4 weeks following a major shift in load³. This is why taking a “down” week every 3-4 weeks may be favorable to allow for mechanoadaptation. Osteoclast activation and resorption takes ~4 weeks, and replacement with new bone can take up to 3 months (1 year for full mineralization). Bone adaptation takes time. In a single day, bone mechanosensitivity is typically restored 4-8 hours after a loading bout. Therefore, running twice per day or adding strength training to one’s routine is most beneficial when implementing adequate rest in between loading bouts. This may look like a morning and evening session in one day for optimal bone loading benefits. Bones become resistant to stress with variant loading. This includes periodization of training, and varying the type of loads including resistance training and plyometrics. Pathophysiology and management BSI are diagnosed on a spectrum ranging from inflammation along the surface of the bone, to high grade injury that shows a true fracture line impacting the cortical part of the bone. It is important to diagnose the severity of the injury through imaging in order to create an appropriate treatment plan including safe return-to-running. Currently, MRI is the best imaging modality to diagnose and guide management of BSI. Treatment includes a rest period from running and sometimes a period of non-weight bearing or partial weight bearing depending on the injury location, severity, and other individual health factors. Concurrently your physical therapist will help develop a plan to identify causative factors, assess biomechanics, strengthen and/or improve coordination of relevant muscles, gradually introduce bone loading exercise, and ultimately return to full running training and competition using an individualized return to run program suited to your needs and goals. Physical therapists can guide you in the diagnosis and treatment of bone stress injuries, along with a team that may include orthopedists, dieticians, and endocrinologist to ensure the most efficient healing process along with taking preventative measures for potential re-injury. It is important to understand how bone stress injuries result, so that athletes can avoid sudden increases in training, allow for relative rest periods throughout a training cycle, and recognize early signs of a BSI.) Sources
