[1] York Univ, Dept Kinesiol & Hlth Sci, N York, ON M3J 1P3, Canada
[2] Michigan State Univ, Inst Study Youth Sports, E Lansing, MI 48824 USA
[3] Washington Univ, Sch Med, Dept Psychiat, Div Biostat, St Louis, MO 63110 USA
[4] Washington Univ, Sch Med, Dept Genet, St Louis, MO 63110 USA
[5] Univ Laval, Div Kinesiol, Dept Prevent Med, Ste Foy, PQ G1K 7P4, Canada
[6] Louisiana State Univ, Pennington Med Res Ctr, Baton Rouge, LA 70803 USA