title: VO2 Off Transient Kinetics in Extreme Intensity Swimming.
abstract: Inconsistencies about dynamic asymmetry between the on- and off- transient responses in oxygen uptake are found in the literature. Therefore, the purpose of this study was to characterize the oxygen uptake off-transient kinetics during a maximal 200-m front crawl effort, as examining the degree to which the on/off regularity of the oxygen uptake kinetics response was preserved. Eight high level male swimmers performed a 200-m front crawl at maximal speed during which oxygen uptake was directly measured through breath-by-breath oxymetry (averaged every 5 s). This apparatus was connected to the swimmer by a low hydrodynamic resistance respiratory snorkel and valve system.
  
  
  RESULTS
  The on- and off-transient phases were symmetrical in shape (mirror image) once they were adequately fitted by a single-exponential regression models, and no slow component for the oxygen uptake response was developed. Mean (± SD) peak oxygen uptake was 69.0 (± 6.3) mL·kg(-1)·min(-1), significantly correlated with time constant of the off- transient period (r = 0.76, p < 0.05) but not with any of the other oxygen off-transient kinetic parameters studied. A direct relationship between time constant of the off-transient period and mean swimming speed of the 200-m (r = 0.77, p < 0.05), and with the amplitude of the fast component of the effort period (r = 0.72, p < 0.05) were observed. The mean amplitude and time constant of the off-transient period values were significantly greater than the respective on- transient. In conclusion, although an asymmetry between the on- and off kinetic parameters was verified, both the 200-m effort and the respectively recovery period were better characterized by a single exponential regression model. Key pointsThe VO2 slow component was not observed in the recovery period of swimming extreme efforts;The on and off transient periods were better fitted by a single exponential function, and so, these effort and recovery periods of swimming extreme efforts are symmetrical;The rate of VO2 decline during the recovery period may be due to not only the magnitude of oxygen debt but also the VO2peak obtained during the effort period.
authors.affiliation: Centre of Research, Education, Innovation and Intervention in Sport, Faculty of Sport, University of Porto , Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Sousa
authors.forename: Pedro
authors.initials: P
authors.lastname: Figueiredo
authors.forename: Kari L
authors.initials: KL
authors.lastname: Keskinen
authors.forename: Ferran A
authors.initials: FA
authors.lastname: Rodríguez
authors.forename: Leandro
authors.initials: L
authors.lastname: Machado
authors.forename: João P
authors.initials: JP
authors.lastname: Vilas-Boas
authors.forename: Ricardo J
authors.initials: RJ
authors.lastname: Fernandes
keywords: Swimming; front crawl; oxygen uptake kinetics; recovery