Change point in VCO2 during incremental exercise test: a new method for assessment of human exercise tolerance

The main purpose of this study was to present a new method to determine the level of power output (PO) at which (V) over dot CO2 during incremental ex ercise test (IT) begins to rise non-linearly in relation to power output (P O) - the change point in (V) over dot CO2 (CP-(V) over dot CO2). Twenty-two healthy non-smoking men (mean +/- SD: age 22.0 +/- 0.9 years; body mass 74 .5 +/- 7.5 kg; height 181 +/- 7 cm; (V) over dot O-2max 3.753 +/- 0.335 l m in(-1)) performed an IT on a cycloergometer. The IT started at a PO of 30 W , followed by gradual increases of 30 W every 3 min. Antecubital venous blo od samples were taken at the end of each step and analysed for plasma lacta te concentration [La](pl), blood PO2, PCO2 [HCO3-](b) and [H+](b) In the de tection of the change-point (V) over dot CO2 (CP-(V) over dot CO2), a two-p hase model was assumed for the 'third-minute-data' of each step of the test . In the first phase, a linear relationship between (V) over dot CO2 and PO was assumed, whereas in the second, an additional increase in (V) over dot CO2 was allowed, above the values expected from the linear model. The PO a t which the first phase ends is called the change point in (V) over dot CO2 . The identification of the model consists of two steps: testing for the ex istence of the change point, and estimating its location. Both procedures a re based on suitably normalized recursive residuals (see Zoladz et al. 1998 a. Eur J Appl Physiol 78, 369-377). In the case of each of our subjects it was possible to detect the CP-(V) over dot CO2 and the CP-(V) over dot O-2 as described in our model. The PO at the CP-(V) over dot CO2 amounted to 13 4 +/- 42 W. The CP-(V) over dot O-2 was detected at 136 +/-: 32 W, whereas the PO at the LT amounted to 128 +/- 30 W and corresponded to 49 +/- 11, 49 +/- 8 and 47 +/- 8.6% (V) over dot O-2max,O- respectively, for the CP-(V) over dot CO2, CP-(V) over dot O-2 and the LT. The [La](pl) at the CP-(V) ov er dot CO2 (2.65 +/- 0.76 mmol L-1), at the CP-(V) over dot O-2 (2.53 +/- 0 .56 mmol L-1) and at the LT (2.25 +/- 0.49 mmol L-1) were already significa ntly higher (P < 0.01, Students t-test) than the value reached at rest (1.8 6 +/- 0.43 mmol L-1). Our study illustrates that the CP-(V) over dot CO2 an d the CP-(V) over dot O-2 occur at a very similar power output as the LT. W e therefore postulate that the CP-(V) over dot CO2 and the CP-(V) over dot O-2 be applied as an additional criterion to assess human exercise toleranc e.