Time to Exhaustion at Traditional Physiological Indicators in Runners: Between-Subject and Between-Day Variability

BACKGROUND: The maximum oxygen uptake (V˙O2max), respiratory compensation point (RCP), and maximal lactate steady state (MLSS) are indicators used to assess athletes' performance. There is scarce information available on the tolerable duration of exercise (time to exhaustion [TTE]) while running at these physiological indicators. We aimed to analyze the TTE when running at these indicators, as well as to determine their between-subject variability and within-subject reliability. METHODS: Thirteen male athletes volunteered to participate (V˙O2max=60.2[4.2] mL·kg-1·min-1). Participants V˙O2max, RCP, and MLSS were assessed through treadmill testing, and they performed 2 TTE tests on different occasions at the speed corresponding to each indicator, during which blood lactate, heart rate, and perceptual responses were measured. RESULTS: TTEs were 03:38 (00:40), 10:58 (02:59), and 56:42 (13:02) mm:ss at the V˙O2max, RCP, and MLSS, respectively. A moderate between-subject variability was observed (coefficient of variation = 18.3%, 27.3%, and 23.0% for V˙O2max, RCP, and MLSS), but no significant associations were found between TTEs and other fitness indicators, such as the speed at which these intensities occurred, nor between TTEs and V˙O2max (all r < .1; P > 0.2). A high within-subject (ie, between-day) reliability was observed for the TTE at all indicators (coefficient of variation of 4.4%, 4.8%, and 6.4% for V˙O2max, RCP, and MLSS, respectively, and intraclass correlation coefficient of .94 and .97, and .90, respectively). CONCLUSIONS: Given their high within-subject reliability and their independence from other traditional physiological indicators of performance, TTE tests could be used for performance monitoring and for training prescription purposes.