Background: Durability, defined as the ability to sustain performance following efforts above critical power (CP), is a critical determinant of elite cycling performance, yet its role in junior cyclists remains underexplored despite its relevance for talent identification. Objective: This study aimed to compare physiological profiles and high-intensity durability between an international-level group (ILG) and a national-level group (NLG) of junior cyclists, establishing normative values for talent detection. Methods: Forty-six male junior cyclists (ILG, n = 20; NLG, n = 26) were evaluated over a full season. CP, maximal aerobic power, and power-output decay (percentage of decay) after energy expenditures above CP (25-200 kJ) were measured using field-derived data across 6 durations (5 s to 30 min). Independent t tests and linear mixed models assessed group differences (P < .05). Results: ILG demonstrated higher CP (383 vs 341 W, P = .003), maximal aerobic power (ILG 434 [54] W vs NLG 391 [44] W, P = .004), and minutes above CP (137 vs 113 min, P = .022) than NLG. NLG exhibited lower percentage of decay at 1 minute (-4.37%, P = .016), suggesting greater durability in short efforts. However, ILG showed lower percentage of decay at 5 to 30 minutes (eg, 1.7% at 5 min, P = .001), reflecting endurance capacity. Interindividual variability in percentage of decay (36%) underscored diverse fatigue responses among cyclists. Conclusion: ILG`s aerobic advantage and durability in prolonged efforts, contrasted with NLG`s resilience in short efforts, highlight durability after work above CP as a talent marker. Normative percentage-of-decay values provide benchmarks for junior talent identification.
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