The present research addresses a curious finding: how learning physical principles enhanced athletes' biking performance but not their conceptual understanding. The study involves a model-based triathlon training program, Biking with Particles, concerning aerodynamics of biking in groups (drafting). A conceptual framework highlights several forms of access to understanding the system (micro, macro, mathematical, experiential) and bidirectional transitions among these forms, anchored at the common and experienced level, the macro-level. Training was conducted separately with two groups, both 14-17 years old youth: an elite junior triathletes team (experts; 4 male, 3 female) and a local team (hobbyists; 6 male, 3 female). The goal was to explore whether agent-based models of bikers and air particles could be used to enhance athletes' understanding and performance, and whether this depends on expertise. The study lasted 3 days and included lectures, discussions, guided exploration of models, inventing new tactics, and biking in practice. Data included questionnaires, interviews, videotapes, and performance measures of heart-rate and biking duration. Athletes' designs were innovative and diverse, expressing well-known and new features in the sport. Local features were more dominant than global features. Their performance in bicycle drafting increased dramatically, with a gain of 20%, at both individual and group levels. The experts mainly reduced their times. Hobbyists mainly reduced their effort. Some conceptual change was evidenced for the complex systems components but not for drafting. Results are discussed in light of learning about complex systems and the balance between cognitive-verbal and motor learning within competitive sports.