STRENGTH TRAINING AS A PREDICTOR OF EXERCISE-RELATED LOWER EXTREMITY STRESS FRACTURE IN YOUNG MALES 1336

Abstract

The purpose of this prospective cohort study was to determine the association between prior strength training, aerobic fitness, and the occurrence of lower extremity (LE) stress fractures (SF) in young males undergoing a rigorous physical training program. Subjects were male U.S. Marine Corps (USMC) recruits (n=2214) ages 17-34 years, who reported to boot camp during a seven week enrollment period. Prior strength training and aerobic fitness were assessed by a questionnaire. An objective measure of aerobic fitness was also assessed, utilizing a standardized USMC 1.5 mile run test administered before the onset of boot camp training. Subjects were then followed through the 11 weeks of boot camp training for SF outcome. SF was determined by a medical record review at the completion of training and SF was defined by clinical presentation and confirmed by radiograph and/or scintigram. Forty-nine subjects (2.2%), developed a total of 56 SFs. Recruits who had performed LE weight training ≥ 4 times per week had a significantly higher incidence (5.3%) of SF (RR = 2.54, 95% CI 1.25, 5.16) when compared to those who had performed ≤ 4 times per week (2.1%). Recruits entering training with low levels of aerobic fitness (n=503) experienced 17 (3.4%) SF and those who had fair or better entry level aerobic fitness (n=1583) experienced 32 (2%) SF. Recruits whose aerobic fitness was poor and who had performed LE weight training ≥ 4 times per week were at greater risk of developing SF (17.4%) than those who performed less or no LE strength training(3.3% SF) [RR = 6.84, 95% CI 2.39, 19.57]. Our data suggest that high volumes of regular LE strength training, in the absence of aerobic training, may increase the risk of SF occurrence in young males undergoing a rigorous physical training program.