Oxygen uptake does not increase linearly at high power outputs during incremental exercise test in humans

Abstract

A group of 12 healthy non-smoking men [mean age 22.3 (SD 1.1) years], performed an incremental exercise test. The test started at 30 W, followed by increases in power output (P) of 30 W every 3 min, until exhaustion. Blood samples were taken from an antecubital vein for determination of plasma concentration lactate [La-]pl and acid-base balance variables. Below the lactate threshold (LT) defined in this study as the highest P above which a sustained increase in [La-]pl was observed (at least 0.5 mmol x l[-1] within 3 min), the pulmonary oxygen uptake (VO2) measured breath-by-breath, showed a linear relationship with P. However, at P above LT [in this study 135 (SD 30) W] there was an additional accumulating increase in VO2 above that expected from the increase in P alone. The magnitude of this effect was illustrated by the difference in the final P observed at maximal oxygen uptake (VO2max) during the incremental exercise test (Pmax,obs at VO2max) and the expected power output at VO2max(Pmax,exp at VO2max) predicted from the linear VO2-P relationship derived from the data collected below LT. The Pmax,obs at VO2max amounting to 270 (SD 19) W was 65.1 (SD 35) W (19%) lower (P < 0.01) than the Pmax,exp at VO2max. The mean value of VO2max reached at Pmax,obs amounted to 3555 (SD 226) ml x min(-1) which was 572 (SD 269) ml x min(-1) higher (P < 0.01) than the VO2 expected at this P, calculated from the linear relationship between VO2 and P derived from the data collected below LT. This fall in locomotory efficiency expressed by the additional increase in VO2, amounting to 572 (SD 269) ml O2 x min(-1), was accompanied by a significant increase in [La-]pl amounting to 7.04 (SD 2.2) mmol x l(-1), a significant increase in blood hydrogen ion concentration ([H+]b) to 7.4 (SD 3) nmol x l(-1) and a significant fall in blood bicarbonate concentration to 5.78 (SD 1.7) mmol x l(-1), in relation to the values measured at the P of the LT. We also correlated the individual values of the additional VO2 with the increases (delta) in variables [La-]pl and delta[H+]b. The delta values for [La-]pl and delta[H+]b were expressed as the differences between values reached at the Pmax,obs at VO2max and the values at LT. No significant correlations between the additional VO2 and delta[La-]pl on [H+]b were found. In conclusion, when performing an incremental exercise test, exceeding P corresponding to LT was accompanied by a significant additional increase in VO2 above that expected from the linear relationship between VO2 and P occurring at lower P. However, the magnitude of the additional increase in VO2 did not correlate with the magnitude of the increases in [La-]pl and [H+]b reached in the final stages of the incremental test.

Relationship between work rate and oxygen uptake in mitochondrial myopathy during ramp-incremental exercise

“…In the present study, we confirm previous observations that S 2 is steeper than S 1 in normal subjects, probably reflecting the contribution of the O 2 slow component (2,3,5,29). This pattern, however, contrasted with that found in patients with MM who showed a consistently lower S 2 /S 1 ratio at the same pedaling rate compared to normal subjects.…”

“…As mentioned, the Δ O 2 /ΔWR relationship (mL·min -1 ·W -1 ) was calculated to obtain an index of the overall gain of the O 2 response, i.e., in disease states, reduced values would indicate a greater reliance on anaerobic sources of ATP regeneration (1,2). Considering that the GET could distort the linearity of the response (due to an even greater reliance on anaerobic metabolism) (3,5), the Δ O 2 /ΔWR slope was determined using linear regression analysis over three segments: S 1 , from the start of O 2 increase during exercise to the GET; S 2 , from the GET to either peak O 2 or where O 2 began to level off, and S T , over the range of S 1 + S 2 .…”

“…Published April 11, 2011. The rate (Δ) of change in oxygen consumption ( O 2 ) relative to power output (work rate, WR) during rampincremental exercise depends on the ability of the cardiocirculatory system to deliver, and the muscle capacity to extract, O 2 from arterial (capillary) blood (1,2). The Δ O 2 / ΔWR relationship is influenced by the gas exchange threshold (GET) with most investigators describing a bi-linear response, i.e., a sub-GET S 1 slope flatter than a supra-GET S 2 slope (3)(4)(5). The analysis of the total Δ O 2 /ΔWR slope (S T ) and its components can provide useful information about the adequacy of the aerobic responses to exercise in health and disease.…”

Curvilinear VO2:Power Output Relationship in a Ramp Test in Professional Cyclists: Possible Association with Blood Hemoglobin Concentration.

“…For instance, VO 2 max values obtained from gradual protocols can be significantly higher (9-17%) than the expected VO 2 at the final workload predicted from the previous linear relationship between VO 2 and workload below the LT [4,6,7].Although some reports have studied the etiology of this nonlinear increase in the VO 2 :power output relationship during incremental exercise (also termed "excess" VO 2 ) [1][2][3][4][5][6][7], some controversy exists and more research is needed. Jones et al…”

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Previous research with healthy, not highly trained humans has shown that the VO 2 :workload relationship shows a nonlinear increase after the lactate threshold (LT) is exceeded during incremental exercise tests [1][2][3][4][5][6][7]. For instance, VO 2 max values obtained from gradual protocols can be significantly higher (9-17%) than the expected VO 2 at the final workload predicted from the previous linear relationship between VO 2 and workload below the LT [4,6,7].

Although some reports have studied the etiology of this nonlinear increase in the VO 2 :power output relationship during incremental exercise (also termed "excess" VO 2 ) [1][2][3][4][5][6][7], some controversy exists and more research is needed.

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