Study aim: The aim of this study was to analyze the effectiveness of polarized (Pol) and threshold (TR) training in youth triathletes (15–18 years). Material and methods: Female youth triathlete subjects taking part in systematic training (n = 42, n(Pol) = 21; n(TR) = 21; at the beginning age(Pol) = 14.63±1.25 years; age(TR) = 14.61 ± 0.89 years) were studied. In this 3-year-long research, anthropometric characteristics and performance were measured, using a spiroergometric, maximal exercise test. Run time spent on a treadmill and physiological data were analyzed. Results: There were no significant differences in anthropometric variables during the study period, but a difference was observed between the two groups in heart rate at the third year. Relative oxygen uptake (rVO2), ventilation (VE) and performance (Time) increased significantly (p < 0.05) in the Pol group, suggesting that this method can also be successful in youth training. Conclusions: Our study results support other research findings demonstrating the effectiveness of polarized training. Further expansion of our sample is necessary to provide guidance for youth triathlon training.