Objectives: To examine 1) the contribution of physiological performance variables to Olympic-distance (OD) triathlon performance, and 2) the links between an 8-wk intensified training plus competition preceding the main OD triathlon race and the changes in the physiological status in triathletes. Study Design: An observational longitudinal study. Methods: Endurance performance variables during maximal incremental running and cycling tests, and average velocity during an all-out 400-m swimming performance test (V400) were assessed before (T1) and after (T2) the intensified training in 7 recreational-level triathletes. Results: Overall main OD triathlon time was extremely largely (r 5
0.94; P 5 0.01) correlated with peak running velocity (PRV). Best correlation magnitude between exercise modes? partial race times and the corresponding specific physiological criterion tests was observed for swimming (r 5= -0.97; P < 0.001). Improvement in V400 (2.9%), PRV (1.5%) and submaximal running blood lactate concentration (17%) was observed along the training period, whereas no changes were observed in the cycling endurance performance variables. Higher volume of training plus competition at high intensity zones during cycling, running and swimming were associated with lower improvements or declines in their corresponding exercise mode-specific criterion performance variables (r 5 0.81-0.90; P 5 0.005-0.037). Conclusion: Results indicate that: 1) PRV is highly associated with overall OD triathlon performance, and 2) spending much time at high relative intensities during swimming, cycling or running may lead, in a dose-response manner, to lower improvements or decreases on those exercise-specific physiological performance variables. This may favor the emergence of overreaching or diminished performance.  Kulcsszavak: aerobic training, exercise testing, physical fitness, training load monitoring, exercise prescription, endurance performance prediction