Dr. Ernst B. Zwick is a board certified orthopedic surgeon specialized in pediatric orthopedics. Interested in aspects of growth, maturation and development he put the focus of his work on developing implementation plans for Long-Term-Player-Development (LTPD) concepts. His team developed a method to estimate the biological age of children and teenagers, which allows to individualize LTPD concepts. The individualization in coaching and training is essential to maximize fun and to prevent drop out and burn out in youth sports.