Moesch et al. (2011) conducted a survey in 148 elite, and 95 near-elite Danish athletes. At the time, the athletes were 24.5 years old, on average, and had specialized in either: track and field, weightlifting, cycling, rowing, swimming, or skiing. The elite athletes specialized in their respective sports ~3.5 later than their near-elite counterparts. Additionally, the elite athletes accrued significantly less sport-specific practice hours during adolescence (before the age of 18), compared with their near-elite counterparts.
For more details about this study, you can read the paper here.
For a review of the relationship between early sport specialization and long-term athletic success, you can read my review of the research here.
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