Pretraining And Menstrual Factors Associated With Stress Fracture In Recruits

Abstract

Stress fractures account for substantial morbidity, especially for young women undergoing U.S. Marine Corps basic training. PURPOSE To examine pretraining characteristics that may identify women at increased risk of stress fractures during boot camp. METHODS We prospectively followed 813 women undergoing basic training at the Marine Corps Recruit Depot (MCRD), Parris Island, in 1999. Data collected included performance on a timed run, anthropomorphic measurements, and a baseline questionnaire highlighting exercise and health habits. The women were followed throughout the 13 weeks of boot camp for occurrence of stress fractures. Stress fracture was confirmed by clinical diagnosis, positive radiograph, and/or bone scan. RESULTS Fifty-six (6.9%) had 66 confirmed lower extremity stress fractures, with the most common sites being the tibia (57.6%), pelvis (13.6%), and femur (12.1%). Logistic regression models revealed that low physical fitness (a slower time on the initial run test)(OR=3.32; 95% CI, 1.4–8.1), secondary amenorrhea (6 or more consecutive months without menses during the past year) (OR=3.83; 95% CI, 1.4–10.3], and delayed age of menarche (13 years or older) (OR=2.13; 95% CI, 1.1–4.0) were significantly associated with the occurrence of stress fractures during boot camp. Recruits who participated in lower body weight training 2 or more times/weekly consistently for 7 or months/year were less likely to incur a stress fracture (1.5%) than recruits who performed lower body weight training 0–6 months/year (7.9%; p<0.036). CONCLUSIONS Consistent with previous studies, we found that low aerobic fitness is a modifiable risk factor to reduce training-related stress fracture. In addition, we also found lower body weight training to be another modifiable factor to decrease stress fracture during training. These findings suggest that stress fractures may be minimized if women entering MCRD training actively participate in pretraining activities designed to improve aerobic fitness and increase lower body strength. Furthermore, women reporting secondary amenorrhea during the previous year or delayed menarche may need additional observation during training. This work was supported by the Naval Health Research Center under Work Unit No. 60213.