Response to the letter of M. Brugnoli
1. In the Aquatrainer, the Xowmeter is positioned at the end of a long corrugated hose, and therefore, the temperature of the exhaled gases before being measured is assumed to be the same as that of the surrounding environment (i.e., ambient temperature). This requires a signiWcant expiratory BTPS correction. The user is thus requested to enter in the appropriate input Weld (i.e., temperature @ Xowmeter) the measured ambient temperature.
Comparison of gas exchange data using the Aquatrainer® system and the facemask with Cosmed K4b2 during exercise in healthy subjects
The aim of this study was to determine the level of agreement between the new Aquatrainer® system and the facemask in the assessment of submaximal and maximal cardiopulmonary responses during exercise performed on ergocycle. Twenty-six physically active healthy subjects (mean age: 41 ± 14 years) performed a submaximal constant work test followed by maximal incremental exercise test on ergocycle, one with cardiopulmonary responses measured using the Cosmed K4b2 facemask, the other using the Cosmed K4b2 Aquatrainer®. Using the Aquatrainer®, the gas exchange variables at 100 W were significantly lower for VO2 (1,483 ± 203 vs. 1,876 ± 204 ml min−1, P < 0.0001), VCO2 (1,442 ± 263 vs. 1,749 ± 231 ml min-1, P < 0.0001), VE (38 ± 5 vs. 44 ± 6 l min−1, P < 0.0001), and VT (1.92 ± 0.47 vs. 2.18 ± 0.41 l, P < 0.0001) relative to facemask. The bias ±95% limits of agreement (LOA) for VO2 was 393 ± 507 ml min−1 for the submaximal constant work test at 100 W and 495 ± 727 ml min−1 for VO2max. At maximal intensity, cardiopulmonary responses measured with the Aquatrainer® system were significantly lower for: VO2 (2,799 ± 751 vs. 3,294 ± 821 ml min−1, P < 0.0001), VCO2 (3,426 ± 836 vs. 3,641 ± 946 ml min−1, P = 0.012), VE (98 ± 21 vs. 108 ± 26 l min−1, P = 0.0009) relative to facemask. A non-constant measurement error [interaction effect: (facemask or aquatrainer) × power] was noted from 60 to 270 W for VO2 (ml min−1), VCO2 (ml min−1), ventilation (l min−1) (P < 0.0001) and VT (l, P = 0.0001). Additional studies are required to detect the main sources of error that could be physical and/or physiological in nature. Due to the significant measurement error, the new Aquatrainer® system should be used with extreme caution in filed testing conditions of swimmers.
VO2max, protocol duration, and the VO2 plateau.
PURPOSE
The purpose of this study was to compare VO2max, VO2-time slopes at the end of the protocol (last 30 s), and the presence of a VO2 plateau (VO2-time slope < 0.05 L.min(-1) during the last 30 s) across four protocol durations (5, 8, 12, and 16 min) during incremental cycling exercise to VO2max.


METHODS
Eight male (23.8 +/- 3.2 yr) and eight female (26.0 +/- 8.9 yr) subjects of moderate to high fitness levels participated in the study.


RESULTS
VO2max was significantly higher in men than in women for each protocol duration, with main effect means of 4.23 versus 2.84 L.min(-1), respectively. For women, VO2max did not differ between any protocol duration. For men, VO2max for the 8-min protocol (4.44 +/- 0.39 L.min(-1)) was significantly higher than for all other protocol durations. Analysis of covariance, using the highest VO2max as the covariate, removed all protocol-duration significance for men. The VO2 slope for the final 30 s of each test was significantly lower for the 16-min protocol compared with the 5-min protocol, for both men and women. The ventilation threshold across four protocols was similar, at approximately 76% of VO2max for both men and women.


CONCLUSIONS
The protocol duration of tests to VO2max should be between 8 and 10 min for healthy, moderately to highly trained subjects.