Stress fracture, also known as a hairline fracture, is a fatigue-induced fracture of the bone caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated trauma from repeated submaximal loading, such as running or jumping. Because of this mechanism, stress fractures are common overuse injuries in athletes. Stress fractures can be described as a very small sliver or crack in the bone. Stress fractures most frequently occur in weight-bearing bones, such as the tibia (bone of the lower leg), metatarsals, and navicular bones (bones of the foot). Less common are fractures to the femur, pelvis, and sacrum.

One method of avoiding stress fractures is to add more stress to the bones. Though this may seem counter-intuitive (because stress fractures are caused by too much stress on the bone), moderate stress applied to the bone in a controlled manner can strengthen the bone and make it less susceptible to a stress fracture. An easy way to do this is to follow the runner’s rule of increasing distance by no more than 10 percent per week. This allows the bones to adapt to the added stress so they are able to withstand greater stress in the future. Strengthening exercises also help build muscle strength in the legs and will help to prevent them from becoming fatigued too quickly, allowing them to absorb the strain of running for longer periods of time. Key muscles that need strengthening with lower leg stress fractures are the calves and the shin muscles.

Runners often suffer from overuse injuries or repetitive stress injuries. These include stress fractures, stress reactions, tendinitis, meniscal tears, ITB Friction syndrome, and exacerbation of pre-existing arthritis. Stress fractures, if not diagnosed and treated, can develop into complete fractures. Depending on a variety of factors (including weight, running surface and shoe durability), runners should replace their shoes every 300-700 miles to allow adequate mid-sole cushioning. A change in running surfaces can also help prevent stress fractures. However, it is also argued that cushioning in shoes actually causes more stress by reducing the body’s natural shock-absorbing action, increasing the frequency of running injuries. Muscle strength training is usually used to help dissipate the forces transmitted to the bones. During exercise that applies more stress to the bones, it may help to increase calcium and vitamin D intake, depending on the individual. Also, it is important to monitor diet, because nutrition plays a vital role in bone development.