GAS ANALYSIS AND EXERCISE TESTING FOR CONDITIONING CONTROL IN SWIMMERS: TECHNOLOGY AND SAMPLING STRATEGIES

During the last 30 years, the application of technology to sport sciences and exercise physiology lead to new research approaches to study cardiorespiratory parameters in swimming. Among the numerous parameters resulting from a cardiopulmonary exercise test (CPET), oxygen uptake (VO2) is widely recognized as the most indicative to measure individual exercise intensity in endurance events. Indeed, maximal oxygen consumption (VO2max) represents an objective and reliable measure of maximal aerobic exercise response [10, 16, 23]. Before the 1990s, VO2 was measured with Douglas Bag or mixing chamber techniques while the swimmer was performing in a flume or in a swimming pool [5, 17, 18, 34]. Presently, the availability of modern breath-by-breath (BxB) technologies for gas analysis enables the acquisition of precise and reliable data in real time [7] using new research methodologies to study the physiological responses to exercise both in laboratory and field conditions [11, 22, 27, 32]. The development of the first portable telemetry gas analyzer (Cosmed K2, Italy) opened up the doors of gas analysis in swimming, allowing direct measurements through the use of a face mask, a flow meter, and an O2 gas analyzer [20]. This innovative piece of technology that evolved to the Cosmed K4 and later to the K4b2 system (Cosmed K4b2, Italy), allowed the execution of a BxB analysis of cardiopulmonary parameters [6, 7, 15, 25]. At the technological progresses applied to gas analysis followed the optimization of the gas collection technique used to collect expiratory gasses in swimming through snorkel and a valve system. The first snorkel device designed by Toussaint and co-authors in 1987 [33], was a system with a dead space of 30 ml used in connection to Douglas bag technique. In 1994, Dal Monte et al. [4] designed a new snorkel in carbon fiber with a reduced dead space of 15 ml and improved hydrodynamics compatible with the first portable O2 analyser (Cosmed K2). Keskinen et al. [21] later upgraded the previous snorkel and valves system of Toussaint and co-workers to a more comfortable and efficient model connected to the Cosmed K4b2 (Cosmed S.r.l., Rome, Italy) for real time BxB measurements. The system was tested in real conditions through cycle ergometer CPET analysis showing a high agreement with the standard facemask (3-7% difference in respiratory and gas exchange values) [25]. Rodriguez et al. [30] confirmed the results of Keskinen and co-workers and reported no relevant differences between a smaller and a bigger volume snorkel connected to a gas exchange simulator and a K4b2 gas analyzer. The latest and most accurate snorkel device is the new version of the Cosmed AquaTrainer® validated by Baldari et al. [3]. Resulting from the evolution of the previous model tested by Gayda et al. [14], this device was designed to reduce gas mixtures and lower the internal resistances and turbulence of the air, using an 11.3 ml dead space, two large and flexible tubes of shorter length, larger diameter Hans- Rudolf valves, and a smooth internal valves assembly surface. Baldari and colleagues reported a high correspondence between the new Cosmed AquaTrainer® and the standard facemask in gas concentration and ventilation (proportional and fixed differences were always rejected: Actas do 3º Simpósio Internacional de Força & Condição Física 32 95% CI always contained the value 1 for the slope and the 0 for the intercept). Moreover, thanks to the oval mouthpiece, the soft head connection, and the flexible but stable underwater tubes they observed higher comfort and stability while swimming freely in a swimming pool [3], and with no additional drag effect [29]. At present, the K4b2 connected to the AquaTrainer® snorkel is the most stable and widespread system for CPET analysis in swimming for the assessment of VO2 kinetics in both rectangular and graded protocols [11, 28]. Integrating the BxB analysis with different experimental approaches, this system also allows to study the VO2 kinetic to evaluate the energy cost of swimming using the percentages of VO2max at different exercise intensities [9, 10, 13, 27, 28]. VO2max is defined as the maximum aerobic power of an individual and it is generally accepted as the best measure of the functional limit of the cardiorespiratory fitness [19] and commonly used in swimming as a prerequisite for excellence [12]. However, BxB analysis requires crucial attention because of the variability in measured parameters and the lack of standardized criteria to calculate VO2max at the end of an incremental exercise test. To minimize the inter-breath fluctuations of respiratory parameters, it is necessary to analyze the variability in VO2 related to different sampling intervals at specific exercise intensities [8] and apply analysis strategies like averaging the data from up to 8 repetitions of the same step transitions [2], or averaging across breaths or within discrete time intervals [26]. Moreover, a preliminary check of occasional breath values (over 3 or 4 ± SD VO2 from the local mean) for the exclusion of errant breaths due to swallowing, coughing, sighing not representative of physiological responses and the application of a 3 to 6-breath moving average (smoothing) in BxB VO2 values are necessary to obtain more stable data [3, 10]. Previous studies reported that VO2 plateau is more visible when higher averaging time intervals are used, however VO2max values are systematically higher as fewer breaths were included in an average recommending a short time interval ≤15 to seconds [1, 2, 24, 26]. In swimming only two studies tried to individualize the optimal time-averaging method able to remove variation in VO2 following BxB analysis. Sousa et al. [31] observed higher variability and absolute VO2 values for BxB sampling compared to time averages of 5, 10, 15 and 20 s in a 200-m all-out front crawl effort and that the VO2max is underestimated at the less frequent sampling frequencies. Fernandes et al. [11] later studied the optimal sampling interval for a 200, 300 and 400-m step length using BxB and 5, 10, 15, 20 and 30 seconds average analysis. They observed that sampling intervals ≤15 seconds allow the highest incidence of the VO2 plateau, independent of the step lengths. In conclusion, the AquaTrainer® snorkel and K4b2 system have been successfully used for VO2max testing through BxB analysis in swimming, allowing swimmers to perform incremental tests without movements restrictions in a swimming pool. However, to obtain reliable and stable data from the breath-by-breath analysis, it is necessary to check for eventual errant breaths, apply a 3-6 breaths smoothing and an averaging interval ≤15 seconds.