Energy system contributions during incremental exercise test

Abstract

The main purpose of this study was to determine the relative contributions of the aerobic and glycolytic systems during an incremental exercise test (IET). Ten male recreational long-distance runners performed an IET consisting of three-minute incremental stages on a treadmill. The fractions of the contributions of the aerobic and glycolytic systems were calculated for each stage based on the oxygen uptake and the oxygen energy equivalents derived by blood lactate accumulation, respectively. Total metabolic demand (WTOTAL) was considered as the sum of these two energy systems. The aerobic (WAER) and glycolytic (WGLYCOL) system contributions were expressed as a percentage of the WTOTAL. The results indicated that WAER (86-95%) was significantly higher than WGLYCOL (5-14%) throughout the IET (p < 0.05). In addition, there was no evidence of the sudden increase in WGLYCOL that has been previously reported to support to the "anaerobic threshold" concept. These data suggest that the aerobic metabolism is predominant throughout the IET and that energy system contributions undergo a slow transition from low to high intensity. Key PointsThe aerobic metabolism contribution is the predominant throughout the maximal incremental test.The speed corresponding to the aerobic threshold can be considered the point in which aerobic metabolism reaches its maximal contribution.Glycolytic metabolism did not contribute largely to the energy expenditure at intensities above the anaerobic threshold.

Keywords: Oxygen uptake; aerobic threshold; anaerobic threshold; blood lactate; energy metabolism contribution; onset of blood lactate accumulation.

Figure 1.

Energy system contributions during incremental exercise test expressed as a percentage of the total metabolic demand. Aerobic threshold was determined at the speed correspondent to 2 mmol·l⁻¹ of blood lactate accumulation. Anaerobic threshold was determined at the speed correspondent to 3.5 mmol·l⁻¹ of blood lactate accumulation. Values are given as mean ± SD (n = 10). * Different from glycolytic contribution (p < 0.05).