Time to Exhaustion at the Respiratory Compensation Point in Recreational Cyclists

The time to exhaustion (t(lim)) at the respiratory compensation point (RCP) and whether a physiological steady state is observed at this workload remains unknown. Thus, this study analyzed t(lim) at the power output eliciting the RCP (t(lim) at RCP), the oxygen uptake (VO(2)) response to this effort, and the influence of endurance fitness. Sixty male recreational cyclists (peak oxygen uptake [VO(2peak)] 40–60 mL∙kg∙min(−1)) performed an incremental test to determine the RCP, VO(2peak), and maximal aerobic power (MAP). They also performed constant-load tests to determine the t(lim) at RCP and t(lim) at MAP. Participants were divided based on their VO(2peak) into a low-performance group (LP, n = 30) and a high-performance group (HP, n = 30). The t(lim) at RCP averaged 20 min 32 s ± 5 min 42 s, with a high between-subject variability (coefficient of variation 28%) but with no differences between groups (p = 0.788, effect size = 0.06). No consistent relationships were found between the t(lim) at RCP and the different fitness markers analyzed (RCP, power output (PO) at RCP, VO(2peak), MAP, or t(lim) at MAP; all p > 0.05). VO(2) remained steady overall during the t(lim) test, although a VO(2) slow component (i.e., an increase in VO(2) >200 mL·min(−1) from the third min to the end of the tests) was present in 33% and 40% of the participants in HP and LP, respectively. In summary, the PO at RCP could be maintained for about 20 min. However, there was a high between-subject variability in both the t(lim) and in the VO(2) response to this effort that seemed to be independent of fitness level, which raises concerns on the suitability of this test for fitness assessment.