Response (2021)

Dear Dr. Gladden: We thank our colleagues for their interest (1) and careful reading of our article (2). We have first to acknowledge a mistake in Table 2 when reporting values of relative maximal oxygen consumption (V˙O2max), which were wrong. The correct values are 27.2 ± 4.9 and 24.8 ± 4.0 mL⋅kg−1⋅min−1 before training and 29.5 ± 4.6 and 24.8 ± 3.6 mL⋅kg−1⋅min−1 after training in the HET and NET groups, respectively (see corrected Table 2 hereinafter). Despite this mistake when reporting values in the original Table 2, the statistical results provided in the article were correct; that is, despite a tendency for a larger improvement in relative V˙O2max in HET (ANOVA group–time interaction: F = 4.2, P = 0.054), there was no significant difference in pre–post training changes in relative V˙O2max as opposed to the larger improvements in absolute V˙O2max and maximal power output observed in the HET versus NET groups. In the Results and Discussion sections, we clearly state that changes in absolute (and not relative, despite the statistical tendency indicated previously) V˙O2max were different between groups. We also emphasize potential explanations for the apparent discrepancy between absolute and relative V˙O2max changes, that is, slight (although not significant) changes in individual body mass and lack of statistical power. TABLE 2 - Cardiorespiratory and metabolic responses at maximal exercise during the incremental cycling test in each group before and after training. HET NET Before After Before After V˙O2, mL⋅kg−1⋅min−1 27.2 ± 4.9 29.5 ± 4.6 24.8 ± 4.0 24.8 ± 3.6 RER 1.2 ± 0.1 1.1 ± 0.1 1.1 ± 0.0 1.1 ± 0.0 V˙ E, L⋅min−1 99.5 ± 16.2 110.5 ± 17.3 a 86.1 ± 12.5 84.3 ± 15.8 Heart rate, bpm 156 ± 25 155 ± 22 b 157 ± 17 148 ± 22 b [La], mmol⋅L−1 8.4 ± 2.3 9.2 ± 2.6 8.2 ± 1.8 7.2 ± 1.6 SpO2, % 95 ± 2 94 ± 2 96 ± 2 96 ± 2 SBP, mm Hg 208 ± 31 211 ± 21 196 ± 28 198 ± 27 DBP, mm Hg 90 ± 14 88 ± 15 82 ± 8 81 ± 11 Leg fatigue 7.7 ± 2 8.0 ± 2.0 7.8 ± 1.6 8.4 ± 1.0 Dyspnea 8.2 ± 1.6 8.3 ± 1.8 8.0 ± 1.7 8.4 ± 1.2 Data are mean ± SD.*ANOVA group–time interaction, significantly different from before (P < 0.05).**ANOVA main effect of time, significantly different from before (P < 0.05).DBP, diastolic blood pressure; HET, hypoxic exercise training group; [La], blood lactate concentration; NET, normoxic exercise training group; RER, respiratory exchange ratio; V˙E, minute ventilation; SBP, systolic blood pressure; SpO2, arterial oxygen saturation; V˙O2, oxygen consumption. Figure 1 clearly shows that absolute V˙O2max and maximal power output increased significantly in the HET group only, which is of functional significance for everyday life; that is, subjects are able to provide greater maximal power output for locomotion, and so on. It has also been previously emphasized that changes in absolute V˙O2max are more representative of changes in cardiorespiratory fitness than relative values in obese individuals (3). Figure 1 also shows nonsignificant differences between groups before training, probably because of the slight difference in sex distribution between groups (one female in the HET group, three females in the NET group). The fact that the changes in absolute V˙O2max and maximal power output were larger in the HET group when considering before and after training values as well as percentage changes supports that these changes were not due to slight differences in before-training values between groups. We agree that controlling the training load is of critical importance, and when considering hypoxic exercise training, this involves controlling both the heart rate as an index of cardiorespiratory load and the arterial oxygenation illustrating the hypoxic load. As described and discussed in the article, during each training session, we continuously adjusted both the workload to maintain the heart rate at 75% (±2%) of individual maximal heart rate and the inspiratory oxygen fraction to reach a target pulse oxygen saturation of 80%. This led throughout the training program to mean power outputs of 79 ± 24 W (45% ± 10% of maximal power output) and 73 ± 12 W (50% ± 2% of maximal power output), mean heart rates of 122 ± 23 and 113 ± 15 bpm, and mean pulse oxygen saturations of 79% ± 2% and 95% ± 2% in HET and NET groups, respectively. We believe this method corresponds to the best practice regarding standardized hypoxic exercise training. Although our study is among the first to evaluate the effects of an innovative intervention in obese individuals (i.e., hypoxic exercise training) on maximal exercise capacity and cardiometabolic health status, we acknowledge that further studies are required taking into account dietary intake and spontaneous physical activity and also considering the long-term consequences. We believe that the effort performed in the present study to evaluate a precise and well-controlled hypoxic training intervention will foster further work in this field. Samarmar Chacaroun Stéphane Doutreleau Patrice Flore Samuel Verges Grenoble Alpes University Hospital Echirolles, FRANCE