What is a bone stress injury (BSI) and how do I know I have one? How long will it take to get me back to running? As a physical therapist who treats a lot of runners and as a lifelong runner myself, I have always had a passion for keeping runners running. The act of running can make someone’s day tick along better, can help with consistent sleep, calm the nerves and can even make a runner more fun to be around. It can be social or an act of solitude. It can be alarming for a runner when they start to experience a nagging pain that doesn’t warm up or even worsens as they run. Pain that doesn’t dissipate with a warm-up routine or is vague at first but then becomes localized or intensifies through the run can be a sign of a bone stress injury or BSI. BSI is a general term indicating mechanical load is exceeding the bone’s structural ability to withstand the load. However, BSIs occur on a continuum. One end of that continuum is a stress reaction, the other end can be stress fracture or even a full fracture of the bone. The runner recognizes this as pain that isn’t normally present. BSIs can occur for many reasons whether due to biomechanics or from a nutritional standpoint or a combination of both. As high-school and college cross-country runners prepare now for this upcoming season, they should be aware of the common causes and ways to prevent bone stress injuries.