The purpose of this study was to determine the relationship between the isocapnic buffer (β_isocapnic) and hypocapnic hyperventilation (HHV) phases as well as performance in a short (20-min) and long (90-min) time trial (TT) in trained athletes. In addition, gross (GE, %) and delta (ΔE, %) efficiency were calculated and the relationship between these variables and the average power output (W) in each TT was determined. Thirteen male endurance athletes (Mean ± SD age 31 ± 6 yrs; body mass 75.6 ± 6.3 kg; height 185 ± 6 cm) completed a continuous incremental test to exhaustion for determination of the β_isocapnicand HHV phases. A second submaximal test was used to determine GE and ΔE. The average power output (W) was measured in a 20-min and 90-min cycling TT. The β_isocapnicphase (W) was significantly correlated to the average power output (W) in the 20-min TT (r = 0.58; p < 0.05), but not in the 90-min TT (r = 0.28). The HHV phase (W) was not significantly correlated to the average power output in the 20-min or 90-min TT. No significant correlation was found for GE or for ΔE and performance in the TT. The data from this study shows that β_isocapnictogether with HHV is not likely to be a useful indicator of cycle TT performance of 20- to 90-min duration. Furthermore, GE and ΔE determined from a submaximal incremental stepwise test are not related to cycling TT performance of different duration. Key words: incremental, correlation, metabolism, athletes, fatigue