Abstract
Introduction: The maximal steady state (SS) blood lactate concentration [La-] and oxygen consumption (VO2) during exercise is identifiable by the second threshold from a graded exercise test (GXT). Consequently, these variables rise to peak values during exercise in excess of the maximal SS. Review articles describe the respiratory compensation point (RCP) as a second threshold determinant, but recent research has found the RCP to occur at an intensity that is greater than the maximal SS. Purpose: To determine if exercise to fatigue at RCP in a group of trained athletes represents the maximal [La-] and VO2 SS. Methods: Sixteen cyclists completed a GXT and a sub-maximal test on the same day to identify the power [in watts (W)] at the RCP VO2 from the GXT (GXT-VO2RCP). Two single-blind constant load exercise (CLE) trials were conducted on subsequent days at the RCP W or RCP W plus 10% (RCP+). Expired air was collected continuously and recorded as 1-min averages. Lactate SS was defined as < 1 mMol/L increase from 10-min to 25-min during CLE. Analysis between GXT and CLE variables used one-way ANOVA and analysis over absolute and relative time intervals [% time to fatigue (TTF)] used two-way ANOVA, with an α-level of .05. Results: The GXT-VO2RCP [3.86 (0.75) L/min] was 93% of GXT-VO2peak [4.17 (0.79) L/min]. During the RCP trial, peak VO2 was not different from GXT-VO2RCP, p = .16, and was highly correlated, r = .98, p < .05. The RCP trial peak VO2 was less than GXT-VO2peak, p < .001, whereas the RCP+ trial peak VO2 was not different from GXT-VO2peak, p = .10. Additionally, the RCP trial VO2 at 60% TTF [3.83 (0.76) L/min] and 80% TTF [3.85 (0.81) L/min] were not different from 100% TTF [3.85 (0.80) L/min], p = .98. The 4-minute post-exercise lactate ([La-]post) from the RCP trial [5.36 (2.64) mMol/L] was less than RCP+ [La-]post [7.75 (2.81) mMol/L], p < .001, but the RCP+ [La-]post was not different from GXT [La-]post [8.68 (3.21) mMol/L], p = .26, n = 15. Only five participants exercised for more than 25 minutes at RCP, with a 10-min [La-] of 4.16 (1.8) mMol/L, and a 25-min [La-] of 5.80 (2.9) mMol/L. Conclusion: The results of this study revealed a VO2 SS during RCP from 60% to 100% TTF; and exercise at RCP+ gave a VO2 that was not different from GXT-VO2peak. In support of recent research, the RCP appears to occur at an intensity that is greater than the maximal [La-] SS. Exercise performed to fatigue at the RCP represents the maximal VO2 SS without a corresponding [La-] SS.