a vibratory summation point. Stress fractures commonly occur in sedentary people who suddenly undertake a burst of exercise (whose bones are not used to the task). They may also occur in athletes completing high volume, high impact training, such as running or jumping sports. Stress fractures are also commonly reported in soldiers who march long distances. Muscle fatigue can also play a role in the occurrence of stress fractures. In a runner, each stride normally exerts large forces at various points in the legs. Each shock—a rapid acceleration and energy transfer—must be absorbed. Muscles and bones serve as shock absorbers. However, the muscles, usually those in the lower leg, become fatigued after running a long distance and lose their ability to absorb shock. As the bones now experience larger stresses, this increases the risk of fracture. Previous stress fractures have been identified as a risk factor. Along with history of stress fractures, a narrow tibial shaft, high degree of hip external rotation, osteopenia, osteoporosis, and pes cavus are common predisposing factors for stress fractures Common causes in sport that result in stress fractures include Over training Going back to competition too soon after an injury or illness Going from one event to another without proper training for the second event Starting initial training too quickly Changing habits or the environment like training surface or shoes Diagnosis X-rays usually do not show evidence of new stress fractures, but can be used approximately three weeks after onset of pain when the bone begins to remodel. A CT scan, MRI, or 3-phase bone scan may be more effective for early diagnosis. MRI appears to be the most accurate diagnostic test. Tuning forks have been advocated as an inexpensive alternative for identifying the presence of stress fractures. The clinician places a vibrating tuning fork along the shaft of the suspected bone. If a stress fracture is present, the vibration would cause pain. This test has a low positive likelihood ratio and a high negative likelihood ratio meaning it should not be used as the only diagnostic method. Prevention Altering the biomechanics of training and training schedules may reduce the prevalence of stress fractures. Orthotic insoles have been found to decrease the rate of stress fractures in military recruits, but it is unclear whether this can be extrapolated to the general population or athletes. On the other hand, some athletes have argued that cushioning in