Among the over 20 million regular runners in the United States, 65% report running injuries each year. This study investigated the factors associated with overuse injuries.

This prospective, longitudinal trial, The Runners and Injury Longitudinal Study (TRAILS), involved 300, injury free runners, 18 to 60 years of age. All reported running a minimum of five miles per week and were free of injury for the prior six months. Questionnaires were administered at baseline and at six and 12 months′ follow-up. The patients were contacted every two weeks for a period of two years to inquire about injuries. Overuse injuries were graded as "maintaining full activity despite symptoms" (grade I), "reducing weekly mileage" (grade II) or "interrupted all training for at least two weeks" (grade III)．

Of the 290 participants, 66% sustained at least one overuse running injury, including 73% of the women and 62% of the men. Most of the initial injuries occurred during the first year, with approximately half characterized as grade I. A univariate analysis revealed that factors at baseline which were significantly associated with an increased chance of injury were lower mental health-related quality of life, more negative emotions endorsed on the Positive and Negative Affect Scale, female gender and greater knee stiffness. A multivariable analysis found only knee stiffness to be predictive of injury (odds ratio 1.18)．

This prospective study of adult runners found that overuse injuries are greater among women and among those with greater knee stiffness.