Resumen de Exercise Intensity Thresholds: Identifying the Boundaries of Sustainable Performance.
Daniel A Keir, Silvia Pogliaghi, Federico Fontana, John m. Kowalchuk, Taylor C. Robertson, Donald H. Paterson, Juan M. Murias
AB Critical power (CP), respiratory compensation point (RCP), maximal lactate steady state (MLSS), and deoxyhemoglobin breakpoint ([HHb]BP) are alternative functional indices that are thought to demarcate the highest exercise intensity that can be tolerated for long durations. Purpose: We tested the hypothesis that CP, RCP, MLSS, and [HHb]BP occur at the same metabolic intensity by examining the pulmonary oxygen uptake (V[spacing dot above])O2p and power output (PO) associated with each "threshold." Methods: Twelve healthy men (mean +/- SD age, 27 +/- 3 yr) performed the following tests on a cycle ergometer: i) four to five exhaustive tests for determination of CP, ii) two to three 30-min constant-power trials for MLSS determination, and iii) a ramp incremental exercise test from which the V[spacing dot above]O2p and PO at RCP and [HHb]BP were determined. During each trial, breath-by-breath V[spacing dot above]O2p and ventilatory variables were measured with a metabolic cart and flowmeter turbine; near-infrared spectroscopy-derived [HHb] was monitored using a frequency domain multidistance system, and arterialized capillary blood lactate was sampled at regular intervals. Results: There were no differences (P > 0.05) among the V[spacing dot above]O2p values associated with CP, RCP, MLSS, and [HHb]BP (CP, 3.29 +/- 0.48; RCP, 3.34 +/- 0.45; MLSS, 3.27 +/- 0.44; [HHb]BP, 3.41 +/- 0.46 L[middle dot]min-1); however, the PO associated with RCP (262 +/- 48 W) and [HHb]BP (273 +/- 41 W) were greater (P < 0.05) than both CP (226 +/- 45 W) and MLSS (223 +/- 39 W), which, themselves, were not different (P > 0.05). Conclusions: Although the standard methods for determination of CP, RCP, MLSS, and [HHb]BP are different, these indices occur at the same V[spacing dot above]O2p, suggesting that i) they may manifest as a result of similar physiological phenomenon and ii) each provides a valid delineation between tolerable and intolerable constant-power exercise
