To identify predictors of developing a stress fracture among
adolescent girls during a 7-year period. Prospective cohort
study. Adolescent girls living throughout the United States. A
total of 6831 girls aged 9 to 15 years at baseline in the
Growing Up Today Study, an ongoing prospective cohort study.
Exposures were assessed by self-report questionnaires completed
by adolescent girls in 1996, 1997, 1998, 1999, 2000, 2001, and
2003. The adolescent girls' history of stress fracture,
including age when fracture occurred and site, were reported by
their mothers, who are registered nurses, in 2004. Cox
proportional hazards models were used in the analysis. Main
Outcome Measure Incident stress fracture that occurred between
1997 and 2004. During 7 years of follow-up, 267 girls (3.9%)
developed a stress fracture. Independent of age, age at
menarche, family history of fracture, and hours per week of low-
and moderate-impact activity, hours per week of running (hazard
ratio = 1.13; 95% confidence interval, 1.04-1.23),