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.