Objectives: The current study provided a longitudinal evaluation of the anthropometric and fitness characteristics in junior rugby league players across three annual-age categories (i.e., under 13s, 14s and 15s) considering playing position and selection level.
Design: Longitudinal design.
Methods: Eighty-one junior rugby league players selected to a talent development programme were tracked over a two year period. Anthropometric (height, sitting height, body mass and sum of four skinfolds) and fitness (lower and upper body power, speed, change of direction speed and maximal aerobic power) characteristics were measured on three occasions (i.e., under 13s, 14s and 15s). Repeated measures multivariate analysis of variance (MANOVA) and multivariate analysis of covariance (MANCOVA; controlling chronological and maturational age) analysed changes across annual-age categories in relation to playing position and selection level.
Results: Findings identified significant improvements in anthropometric and fitness characteristics across annual-age categories (p < 0.001). MANOVA and MANCOVA analysis identified significant overall effects for playing position (p < 0.001) and selection level (p < 0.05) throughout the two year period. Interactions between playing position and time were identified for height, vertical jump and estimated VO^sub 2max^ (p < 0.05). Selection level by time interactions were identified for 20 m, 30 m and 60 m sprint (p < 0.05). Conclusions: This study demonstrates the improvement of anthropometric and fitness characteristics within junior representative rugby league players. Interactive effects for playing position and selection level by time highlight the variation in the development of characteristics that occur during adolescence. Tracking the progression of characteristics longitudinally during adolescence, instead of at one-off time points, may assist selection and/or performance assessments within rugby league and other youth sport contexts.