The algorithm used for the calculation of gas exchange affects the estimation of O₂ uptake kinetics at the onset of moderate‐intensity exercise

Figures

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  FIGURE 1. Example of gas exchange data obtained from one volunteer during an experimental session. The experimental protocol included: (a) an initial 5‐min pedalling period at 10 W (10W‐P), (b) two bouts of moderate intensity exercise, lasting 6 min each (1 W/kg, i.e., 55 W in this volunteer; MI‐P), separated by 10 min of pedalling at 10 W, and (c) a final recovery period lasting 8 min while pedalling at 10 W. Pedalling frequency was kept as close as possible to 60 rpm throughout. V˙O2 (upper panel) and V˙CO2 (lower panel) data obtained applying the IND (continuous red line) or the EXP (dashed blue line) algorithms are illustrated. Vertical lines correspond to the start and end times of the two bouts of moderate‐intensity pedalling periods. Shaded areas correspond to the time periods over which the data were averaged, namely, two periods during 10W‐P (BL1 and BL2) and two periods during MI‐P (SS1 and SS2).

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  FIGURE 2. Mean time constants (τ; upper left panel) and mean time delays (T d; middle left panel) of oxygen uptake kinetics are illustrated as a function of the time period removed from the fitting window (ΔT r), as well as the corresponding mean asymptotic standard errors, ASEτ (upper right panel) and ASETd (middle right panel). The corresponding mean response times (MRT) are illustrated in the lower panel. Results obtained for the data yielded by the IND (filled red circles) and the EXP (open blue circles) algorithms are illustrated in all panels. Vertical bars are the standard deviations of the individual parameters obtained running the non‐linear regression procedure with the mono‐exponential model. The differences between the two algorithms with the same ΔT r are illustrated as Cohen's d Z effect sizes (right vertical axis, on a logarithmic scale only for graphical purposes), using different symbols according to the statistical significance (n = 10; two‐tailed paired t‐test; * P < 0.05; ** P < 0.01). The 5 areas of decreasing colour intensity from bottom to top highlight the magnitude of Cohen's d Z according to the commonly used thresholds (namely, ‘trivial’ < 0.2 < ‘small’ < 0.5 <…

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  FIGURE 3. Mean time constants (τ; upper left panel) and mean time delays (T d; middle left panel) of carbon dioxide exhalation kinetics are illustrated as a function of the time period removed from the fitting window (ΔT r), as well as the corresponding mean asymptotic standard errors ASEτ (upper right panel) and ASETd (middle right panel). The corresponding mean response times (MRT) are illustrated in the lower panel. Results obtained for the data yielded by the IND (filled red circles) and the EXP (open blue circles) algorithms are illustrated in all panels. Vertical bars are the standard deviations of the individual parameters obtained running the non‐linear regression procedure with the mono‐exponential model. The differences between the two algorithms with the same ΔT r are illustrated as Cohen's d Z effect sizes (right vertical axis, on a logarithmic scale only for graphical purposes), using different symbols according to the statistical significance (n = 10; two‐tailed paired t‐test; * P < 0.05; ** P < 0.01). The 5 areas of decreasing colour intensity from bottom to top highlight the magnitude of the Cohen's d Z according to the commonly used thresholds (namely, ‘trivial’ < 0.2 <…

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  FIGURE 4. Stacked V˙O2IND (filled red circles; continuous line) and V˙O2EXP (open blue circles; dashed line) time series of the same subjects as in Figure 1. For graphical purposes, data of the 10 repetitions pertaining to the same algorithm were first stacked together, sorted in ascending time and then averaged both in time and in signal intensity over 10 consecutive data points (i.e. the number of repetitions). For both algorithms, the parameters estimated by non‐linear regression with ΔT r = 20 s were used to draw the two lines showing the corresponding kinetics.