 The aerobic fitness is important for mountain bikers, but riders should also be able to generate maximal and supramaximal efforts in some crucial phases of the competition. Although there is an increase interest in high-intensity aerobic training, to investigators knowledge, there are no studies examining the effects of interval INTV or intermittent training INTM in mountain bikers. The aim of this study was to compare the effects of INTV and INTM on aerobic fitness variables peak power output, Wmax, lactate threshold, and onset of blood lactate accumulation but more importantly on performance as measured using a controlled mountain bike race, i.e. simulation. The investigators hypothesized that INTV and INTM training were equally effective in improving Wmax, Lactate threshold and onset of blood lactate accumulation, but INTV was superior in enhancing performance in mountai bike race simulation.This hypothesis is due to studies that have shown higher gains in performance with long duration of aerobic high intensity interval training in comparison to the shorter training at a higher intensity. 