Effect of Computational Method on Accumulated O2 Deficit

Figures

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  Figure 1. (Left) relationship between power and O2 demand for a typical subject (no. 8). O2 uptake was measured at 8–10 min of exercise at nine different constant powers between 88 and 265 W (filled symbols), and a linear regression was calculated based on those data. The highest value (filled diamond) was used in methods M5–M8 (see Figure 2 below). If in addition four measurements at lower powers are included (open symbols), a different relationship with a higher value of the intercept and a lower slope is obtained (dashed line, called method 4). (Right) calculations of the accumulated O2 deficit. O2 uptake was measured during 1 min exercise to exhaustion (here taken from a previous study), giving the accumulated O2 uptake (light dotted area). The accumulated O2 demand is taken as the O2 demand times the duration, reflecting the total energy release in units of oxygen. The accumulated O2 deficit (dark gray area + hatched area at the top) is taken as the accumulated O2 demand minus the accumulated O2 uptake. If the O2 demand is estimated to be lower (here by method 4), the estimated accumulated O2 deficit becomes lower (hatched area at the top not included).

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  Figure 2. Relationship between power and O2 demand for a typical subject (no. 9), and the effects of extrapolations to high powers. (Left) relationships established by methods 1 and 3 (M1 and M3). The relationship of M2 is very close to that of M1, and it is therefore not included. The relationship of the reference method (M0) is shown by the dotted line. A corresponding relationship for M4 is shown in Figure 1. (Right) relationships established by methods 5–8 (M5–M8) using fixed intercepts and one measurement at around 90% of the maximal O2 uptake (point). The line of M5 is very close to that of M0, which is therefore not included.

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  Figure 3. O2 uptake as a function of pedaling frequency. (Left) loadless pedaling of n = 8–11 subjects. (Right) y-intercept of linear regressions of steady-state O2 uptake on power. The data for the latter curve are taken from this study (0.5, 0.75 and 1.5 Hz; n = 8, 10, and 12, respectively, filled symbols) and from Medbø and Tabata (1989) and Medbø et al. (1999; open symbols).

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  Figure 4. Residual plots of the accumulated O2 deficit calculated for four examined test methods (M1–M4) vs. the reference method (M0). The residuals have been taken as the value of the test method less that of the reference method. The data are simulated for exercise to exhaustion within 10 s (250% of max. O2 uptake, ▴), 30 s (200% of max. O2 uptake, ♦), 1 min (150% of max. O2 uptake, ◯), 2 min (120% of max. O2 uptake, ■), and 3.6 min (100% of max. O2 uptake, ∙) as explained in the methods. The dashed line is the zero line, indicating no difference. Note that the y-axes are not scaled equally.

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  Figure 5. Residual plot of the accumulated O2 deficit calculated for four examined test methods (M5–M8) vs. the reference method (M0). The residuals have been taken as the value of the test method less that of the reference method. The data are simulated for exercise to exhaustion within 10 s (250% of max. O2 uptake, ▴), 30 s (200% of max. O2 uptake, ♦), 1 min (150% of max. O2 uptake, ◯), 2 min (120% of max. O2 uptake, ■), and 3.6 min (100% of max. O2 uptake, ∙) as explained in the methods. The dashed line is the zero line, indicating no difference. Note that the y-axes are not scaled equally.