Predictors of stress fracture susceptibility in young female recruits.

BACKGROUND Stress fractures account for substantial morbidity for young women undergoing U.S. Marine Corps basic training. HYPOTHESIS Certain pretraining characteristics identify women at increased risk of stress fractures during boot camp. STUDY DESIGN Cohort study; Level of evidence, 2. METHODS Data collected included baseline performance on a timed run (a measure of aerobic fitness), anthropometric measurements, and a baseline questionnaire highlighting exercise and menstrual status among 2962 women undergoing basic training at the Marine Corps Recruit Depot, Parris Island, in 1995 and 1996. RESULTS One hundred fifty-two recruits (5.1%) had 181 confirmed lower extremity stress fractures, with the most common sites being the tibia (25%), metatarsals (22%), pelvis (22%), and femur (20%). Logistic regression models revealed that having low aerobic fitness (a slower time on the timed run) and no menses during the past year were significantly associated with the occurrence of any stress fracture and with pelvic or femoral stress fracture during boot camp. CONCLUSION These findings suggest that stress fractures may be reduced if women entering Marine Corps Recruit Depot training participated in pretraining activities designed to improve aerobic fitness. Furthermore, women reporting no menses during the previous year may need additional observation during training. CLINICAL RELEVANCE Consistent with previous studies, we found that low aerobic fitness was the only modifiable risk factor associated with stress fractures during boot camp.