Exercise Intensity Thresholds: Identifying the Boundaries of Sustainable Performance

• Published in: Medicine and science in sports and exercise 2015-09, Vol.47 (9), p.1932-1940
• Main Authors: KEIR, DANIEL A, FONTANA, FEDERICO Y, ROBERTSON, TAYLOR C, MURIAS, JUAN M, PATERSON, DONALD H, KOWALCHUK, JOHN M, POGLIAGHI, SILVIA
• Format: Article
• Language: English
• Subjects: Adult; Anaerobic Threshold - physiology; Exercise - physiology; Exercise Test; Hemoglobins - metabolism; Humans; Lactic Acid - blood; Male; Physical Endurance - physiology; Respiratory Mechanics; Young Adult
• ISSN: 0195-9131; 1530-0315
• DOI: 10.1249/MSS.0000000000000613

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. PURPOSEWe tested the hypothesis that CP, RCP, MLSS, and [HHb]BP occur at the same metabolic intensity by examining the pulmonary oxygen uptake (V˙)O2p and power output (PO) associated with each “threshold.” METHODSTwelve healthy men (mean ± SD age, 27 ± 3 yr) performed the following tests on a cycle ergometeri) 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˙O2p and PO at RCP and [HHb]BP were determined. During each trial, breath-by-breath V˙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. RESULTSThere were no differences (P > 0.05) among the V˙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·min); 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). CONCLUSIONSAlthough the standard methods for determination of CP, RCP, MLSS, and [HHb]BP are different, these indices occur at the same V˙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.