Is There an Oxygen Pulse Threshold During Treadmill Running?

Abstract

It has been suggested there are two separate breakpoints in the oxygen pulse (O2 pulse = VO2/heart rate) versus workload relationship during incremental cycle ergometry, corresponding to the first and second turn points in the blood lactate response. It is still unclear if these O2 pulse breakpoints can be detected during treadmill running, and if detected, where these thresholds may be located relative to the gas exchange threshold (GET) and respiratory compensation point (RCP). PURPOSE: This study examined the relationship between O2 pulse and exercise intensity to determine if O2 pulse thresholds could be detected during treadmill running, and, if detected, to compare these O2 pulse thresholds to the GET and RCP. METHODS: Twelve, moderately trained runners (6 men and 6 women; age = 23 ± 3 years; height = 175 ± 8 cm; weight = 71 ± 12 kg) completed an incremental treadmill test to exhaustion for the measurement of gas exchange, ventilation, and heart rate parameters, as well as the determination of VO2 peak. The GET and RCP were determined from the breakpoint in the VCO2 versus VO2 and VE versus VCO2 relationships, respectively. The O2 pulse was plotted against VO2 for each subject and the relationship between these two variables was examined using polynomial regression models (linear and quadratic) at an alpha level of p ≤ 0.05. RESULTS: The mean (± SD) VO2 peak was 3.475 ± 0.959 L·min-1 (48.33 ± 7.30 mL·kg-1·min-1). The GET (2.289 ± 0.617 L·min-1) and RCP (3.029 ± 0.867 L·min-1) occurred at 67 ± 5% and 88 ± 4 % of VO2 peak, respectively. The O2 pulse versus VO2 relationship was best explained by a linear fit (r2 = 0.976 - 1.000) for 9 and a quadratic fit (R2 = 0.985 - 0.996) for 3 of the 12 subjects. Only 1 of the 3 subjects with a quadratic fit for the O2 pulse versus VO2 relationship displayed a response consistent with a plateau in the O2 pulse. CONCLUSIONS: The highly linear relationship between O2 pulse and VO2 for 75% of the subjects indicated that O2 pulse thresholds could not be detected during treadmill running using the O2 pulse versus VO2 relationship. These findings do not support the use of the O2 pulse as a non-invasive measure of fatigue thresholds.