This study investigated whether field-based intermittent tests performed under fatigued conditions better predict Olympic cross-country mountain biking (XCO-MTB) performance, whether prior prolonged exercise reduces power output during these tests, and whether the ability to maintain power output during intermittent tests under fatigue distinguishes competitive level in mountain bikers. Twenty-five male XCO-MTB athletes were tested under "fresh" and fatigued conditions in randomized order, separated by 72 h. Within each condition, participants performed three field-based intermittent tests with work: recovery formats of 30 s:15 s (30/15), 10 s:20 s (10/20), and 3 min:2 min (3/2), in randomized order and separated by 24 h. In the fatigued condition, each intermittent test was immediately preceded by a 140-min fatigue protocol that included repeated efforts at 105%-110% of critical power. Participants were classified as high-performance (HP) or low-performance (LP) based on XCO-MTB individual time-trial (ITT) performance, assessed 72 h after the last test session. All intermittent tests showed large to nearly perfect correlations with XCO-MTB ITT performance (n = 24; r = -0.53 to -0.95; p = 0.007 to p < 0.001), with stronger associations under fatigued conditions. The fatigued 10/20 test expressed relative to body mass was the strongest predictor, explaining 89% of performance variance. Power output decreased across all three tests after the fatigue protocol (n = 25; all p < 0.001), with greater declines in the LP group (˜15%-20%) than in the HP group (˜6%-10%; p = 0.008 to p < 0.001). In conclusion, these findings suggest that the ability to sustain power output during repeated intermittent efforts under fatigue is relevant to XCO-MTB ITT performance and competitive level.
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