Background: Sports specialization has become increasingly common among youth.
Purpose/hypothesis: To investigate the relative importance of specialization vs volume of activity in increasing risk of injury. Hypotheses were that specialization increases the risk of injury and that risk varies by sport.
Study design: Cohort study; Level of evidence, 2.
Methods: A prospective analysis was conducted with data collected from 10,138 youth in the Growing Up Today Study-a prospective cohort study of youth throughout the United States-and their mothers. Activity was assessed via questionnaires in 1997, 1998, 1999, and 2001. Sports specialization was defined as engaging in a single sport in the fall, winter, and spring. Injury history was provided by participants' mothers via questionnaire in 2004. The outcome was incident stress fracture, tendinitis, chondromalacia patella, anterior cruciate ligament tear, or osteochondritis dissecans or osteochondral defect.
Results: Females who engaged in sports specialization were at increased risk of injury (hazard ratio [HR], 1.31; 95% CI, 1.07-1.61), but risk varied by sport. Sports specialization was associated with greater volume of physical activity in both sexes (P < .0001). Total hours per week of vigorous activity was predictive of developing injury, regardless of what other variables were included in the statistical model (males: HR, 1.04; 95% CI, 1.02-1.06; females: HR, 1.06; 95% CI, 1.05-1.08). Among females, even those engaging in 3 to 3.9 hours per week less than their age were at a significantly increased risk of injury (HR, 1.93; 95% CI, 1.34-2.77). In males, there was no clear pattern of risk.
Conclusion: Sports specialization is associated with a greater volume of vigorous sports activity and increased risk of injury. Parents, coaches, and medical providers need to be made aware of the volume threshold above which physical activity is excessive.
Keywords: adolescents; epidemiology; prospective cohort study; sex-based differences.