Risk of Injuries Associated With Sport Specialization and Intense Training Patterns in Young Athletes: A Longitudinal Clinical Case-Control Study
Jayanthi N, Kleithermes S, Dugas L, Pasulka J, Iqbal S, LaBella C · 2020
grade Cquasi-experimentindependentreplicatednumbers spot-checked
Sample
1,208 enrolled; 579 analyzed at 6 months
Population
Young athletes aged 7-18 presenting to sports-medicine or pediatric clinics; mean age 14.1 ± 2.3 y, 53% female
Design
Clinic-recruited longitudinal case-control, 6-month surveys over 3 years. Severe attrition: 579 of 1,208 enrolled (48%) completed baseline plus 6 months; 53% retained at 18 months, 11% at 36 months, so long-run estimates are near-uninterpretable. Sports-medicine clinic recruitment brings surveillance bias; exposures self-reported; specialization confounded with total hours and sport:free-play ratio.
Key findings
Specialization and injury, with the volume confound addressed. Odds ratios of 1.41 (1.06-1.87) and 1.46 (1.04-2.04) come from MULTIVARIABLE models already adjusting for weekly organized-sport hours (the overuse model also adjusts for total weekly physical activity and hours-exceeding-age). The training-volume markers were univariate only. CORRECTION: specialization risk SURVIVES adjustment for training volume — it is not simply a proxy for chronic load. Female sex carried a comparable OR (1.43).
Genetic confound
Not addressed. Heritable growth/maturation timing and connective-tissue phenotypes predict overuse injury; clinic recruitment further selects on injury-prone phenotypes.
Replication notes
Same direction as Bell 2018 and McGuine 2017. No study has randomized specialization, so the volume-vs-specialization confound is unresolved across every replication.
Effects
| Outcome | Metric | Value | Measure | Timing | Vs | Horizon | Class |
|---|---|---|---|---|---|---|---|
| All injuries, HIGH vs LOW specialization | odds ratio | OR 1.41 (95% CI 1.06-1.87) | mixed | retention (real injury outcome); field | none | under-1yr | health |
| Overuse injuries, HIGH vs LOW specialization | odds ratio | OR 1.46 (95% CI 1.04-2.04) | mixed | retention; field | none | under-1yr | health |
| Female sex (benchmark covariate in the same model) | odds ratio | OR 1.43 (1.09-1.83) all injuries; 1.43 (1.05-1.96) overuse — same size as specialization | standardized | retention; field | none | under-1yr | health |
| Training-load markers: weekly sports hours exceeding age in years; sport-to-free-play ratio >2:1 | univariate association with injury | both P<.001 — volume effects at least as strong as specialization | researcher-designed | retention; field | none | under-1yr | health |
| Companion Jayanthi 2015 clinical case-control | odds ratio | OR 1.27 (1.07-1.52) any injury; OR 1.36 (1.08-1.72) serious overuse | mixed | retention; field | none | unclear | health |
Cited by
- Early sport specialization, talent selection, and the relative age effectmixedconf: mediumgc: medium