Relationships between physical fitness and early standing-start kinematic characteristics in adolescent male track cyclists

The early standing-start phase is important for sprint track cycling, yet continuous standing-start kinematics and their relationships with physical fitness remain unclear in adolescent athletes. This study characterized standing-start kinematics, assessed their reliability, and examined their associations with physical fitness in 11 adolescent male track cyclists. Participants completed standing long jump, back squat 1RM, and 30-s cycling sprint tests, followed by three standing-start trials. Continuous trunk and lower-limb kinematics from movement initiation through the first 180° of crank rotation were obtained using markerless motion analysis. The three-trial mean showed high reliability across the six kinematic variables (ICC(A,3) = 0.810–0.965). Relative mean power showed the strongest association with knee range of motion (ρ = 0.700, raw p = 0.0165), but none of the 24 associations remained significant after BH-FDR correction. These findings support repeated-trial assessment for reliable characterization of standing-start kinematics and provide preliminary evidence for further investigation of fitness–kinematic relationships in adolescent track cyclists.