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V[O.sub.2] off transient kinetics in extreme intensity swimming.

Introduction

Oxygen uptake (V[O.sub.2]) kinetics has been analyzed through mathematical modeling of the constant-load exercise onset and offset V[O.sub.2] response. This response profile appears to be of an exponential nature, which could indicate first or second order kinetics operations (DiMenna and Jones, 2009). This analysis has shown that V[O.sub.2] exponentially increases at the onset of moderate exercise with constant power output (on-fast component), reaches a steady state, and rapidly decreases at the offset of moderate exercise (off-fast component) (Kilding et al., 2006; Ozyener et al., 2001; Paterson and Whipp, 1991; Scheuermann et al., 2001). First-order kinetics mandates on/off symmetry, which means that the change in V[O.sub.2] occurring when the contractile activity is ceased must be a mirror image of that which occurred when it was commenced (Rossiter et al., 2005). In the heavy intensity exercise, i.e., at intensities greater than the anaerobic threshold but below the maximal V[O.sub.2], an delayed increase (on-slow component) after the on-fast component is presented (Barstow and Mole, 1991; Barstow et al., 1996; Ozyener et al., 2001; Paterson and Whipp, 1991; Scheuermann et al., 2001), but at the offset only an off-fast component is developed (Ozyener et al., 2001; Scheuermann et al., 2001). At the severe exercise intensity, which is significantly above the anaerobic threshold, and neither V[O.sub.2] nor blood lactate levels can be stabilized (Poole et al., 1988), the on-transient V[O.sub.2] kinetics is reverted to a single-exponential profile (Ozyener et al., 2001), while the off-transient kinetics is retained for a two-component form (Dupond et al., 2010; Ozyener et al., 2001). At the highest intensity--extreme exercise leading to exhaustion before maximal oxygen uptake is attained (DiMenna and Jones, 2009; Hill et al., 2002)--, the V[O.sub.2] on-kinetics response is characterized by the development of an evident fast component, being the slow component phenomenon not developed (Burnley and Jones, 2007; Figueiredo et al., 2011; Whipp, 1994). This area of intensity was recently described (Hill et al., 2002), and, to the best of our knowledge, the V[O.sub.2] off-kinetic profile has never been studied at this particular intensity.

V[O.sub.2] assessment has been carried out mainly in well controlled environments, particularly in exercise laboratories, and the number of studies conducted in field is very scarce (Billat et al., 2002; Fernandes et al., 2008). In fact, the V[O.sub.2] off-transient kinetics is documented in constant-load exercise performed from the moderate to severe intensities. Nevertheless, studies that aim to model the V[O.sub.2] recovery kinetics at extreme intensity exercise were not yet conducted in swimming. In this sense, the purpose of this study is to characterize the V[O.sub.2] off-transient kinetics, examining also the on/off symmetry, during a 200-m front crawl maximal effort performed at extreme intensity. It was hypothesized that an on/off symmetry of the V[O.sub.2] kinetics response would be preserved, although the post-exercise V[O.sub.2] did not match the O2 deficit.

Methods

Participants

Eight highly trained male swimmers volunteered to participate in the study. The participants provided informed written consent before data collection, which was approved by the local ethics committee and was performed according to the declaration of Helsinki. Their mean performance for long course 200-m freestyle was 109.3 [+ or -] 2.0 s, corresponding to 90.3 [+ or -] 3.2% of the 2009 world record for this event. This sample included a finalist and five participants at the European Championships. Individual and mean ([+ or -] SD) values for subjects' main physical and performance characteristics were: age (21.8 [+ or -] 2.4 years), height (184.5 [+ or -] 6.2 cm), body mass (76.1 [+ or -] 6.5 kg), fat mass (10.4 [+ or -] 1.7%) and lean body mass (62.4 [+ or -] 4.4%).

Data collection

In an indoor 25-m swimming pool, with a water temperature of 27[degrees]C, each swimmer performed a 200-m front crawl effort at maximal speed. In water starts and open turns, without underwater gliding, were used. Each swimmer performed a 200-m front crawl maximal effort, according to his best individual 200-m performance and his own experiences, and was encouraged to swim at his best effort; therefore, no visual or acoustic pacing was implemented. V[O.sub.2] kinetics was measured using a telemetric portable gas analyzer ([K4b.sup.2], Cosmed, Italy), which was connected to the swimmer by a low hydrodynamic resistance respiratory snorkel and valve system (Keskinen et al., 2003; Rodriguez et al., 2008), and was calibrated before and after each test. Respiratory variables were continuously monitored after the 200-m effort until baseline V[O.sub.2] values were obtained (after approximately 12 min of recovery the assessment was ended). Swimmers were advised to use continuous rhythmical breathing during swimming, turning and in the recovery period. Expired gas concentrations were measured breath-by-breath and averaged every 5 s for a better temporal resolution (Sousa et al., 2010) in order to reduce inter breath fluctuations ("noise"). Peak oxygen uptake (V[O.sub.2peak]) was considered as the highest value of this sampling interval.

Data analysis

The following equation was used to fit V[O.sub.2] kinetics on the on-transient period:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

where t is the time, [V.sub.b] is the oxygen uptake at the start of the exercise (mL x [kg.sup.-1] x [min.sup.-1]), [A.sub.on] is the amplitude of the fast component (mL x [kg.sup.-1] x [min.sup.-1]), [TD.sub.on] is the time for the onset of the fast component (s) and [[tau].sub.on] stands for the time constant of the fast component, i.e., the time to reach 63% of the plateau of this phase during which physiological adaptations adjust to meet the increased metabolic demand. The cardiodynamic phase was not taken into consideration due to its amplitude insignificant value. The inexistence of a slow component was confirmed by the rigid intervals method, particularly by the difference between the last V[O.sub.2] measurement of the exercise and the value measured in the final 5 s of the 200-m event adapted from Fernandes et al., 2003; Koppo and Bouckaert, 2002).

For the off-transient period, the individual responses were fitted by using both a single (equation 2) and a double exponential (equation 3) regression models for the entire recovery period, in which the exponential term started at the beginning of the off-transient period modeling ([TD.sub.1off] in the equations):

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)

where t is the time, [A.sub.off] represents the amplitude for the exponential term and the [[tau].sub.off] and [TD.sub.off] are the associated time constant and time delay. A nonlinear least squares method was implemented in MatLab for the adjustment of these functions to V[O.sub.2] data.

After a visual exploratory inspection of all V[O.sub.2] curves, and for the sake of numerical stability, it was verified that, due to the extreme exercise intensity in which the 200-m held, all swimmers started the recovery period immediately after the 200-m effort. In this sense and assuming that [TD.sub.1off]=0, the off-transient period was modeled according to the restructure equations:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (4)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (5)

Statistical analysis

For the entire sample, mean and SD computations for descriptive analysis were obtained for all variables and for the entire group of subjects, and were checked for distribution normality with the Shapiro-Wilk test. All statistical procedures were conducted with SPSS 10.05. An F-test was used to compare the single and double exponential regression models best fitting. To compare on- and off-transient parameters Paired sample T-tests were used. Simple linear regression and Pearson's correlation coefficient were computed to indicate the linear relationship between parameters and with swimming time. The level of significance was set at p < 0.05.

Results

The F-test (0.28) showed the homogeneity of both models variances, confirmed also by the equality of their mean values (p=0.98), and therefore, the off-transient response was well described by a single exponential function. In fact, this characterization was not improved by using the double exponential model. In this sense, the on- and off-transient periods are symmetrical in shape (mirror image) once they were adequately fitted by single-exponential functions. An example of the oxygen ([O.sub.2]) uptake on and off kinetics curve is shown in Figure 1.

The mean ([+ or -] SD) values for swimming speed ([200.sub.speed]), V[O.sub.2peak], [A.sub.on], [TD.sub.on], [[tau].sub.on] and [A.sub.off] and [[tau].sub.off] for the 200-m front crawl effort and recovery period are presented in Table 1.

Significant differences were obtained between the on- and off- V[O.sub.2] kinetic parameters (all for p<0.01), and its amplitude was higher in the recovery period. Complementarily to the above referred data, direct relationships were observed between [[tau].sub.off] and [200.sub.speed] (r = 0.77, p = 0.02), [[tau].sub.off] and V[O.sub.2peak] (r = 0.76, p = 0.03) and [[tau].sub.off] and [A.sub.on] (r = 0.72, p = 0.04) (see Figure 2). No significant correlations were found between V[O.sub.2peak] and the other V[O.sub.2] off-transient parameters ([A.sub.off], r = 0.35, for p > 0.05). The absences of significant relationships were also observed between [[tau].sub.on] and [[tau].sub.off] (r = 0.19) and [A.sub.on] and [A.sub.off] (r = 0.5), all with p > 0.05.

[FIGURE 1 OMITTED]

Discussion

The aim of this study was to characterize the V[O.sub.2] off-transient kinetics and to examine the on/off symmetry during a self-imposed 200-m swimming at race pace. We tested the hypothesis that the V[O.sub.2] kinetics response will manifest a symmetric on/off response, even if the post-exercise V[O.sub.2] does not match the [O.sub.2] deficit.

An understanding of the V[O.sub.2] kinetics is considered an important parameter to improve sports training methodology and increase performance in sport (Billat et al., 2001). Furthermore, it was recently suggested that the determinants of exercise tolerance and the limitations to sports performance can be better understood through an appreciation of the physiological significance of the fast and slow components of the dynamic V[O.sub.2] response to exercise (Burnley and Jones, 2007). For a long time, studies regarding [O.sub.2] uptake assessment in swimming were conducted with either Douglas bags (di Prampero et al., 1974; Lavoie and Montpetit, 1986) or mixing chamber gas analyzers (Dal Monte et al., 1994; Demarie et al., 2001). It was only recently that the development of a swimming snorkel suitable for breath-by-breath analysis (Keskinen et al., 2003; Rodriguez et al., 2008) allowed assessing V[O.sub.2] dynamics in swimming pool conditions through direct oxymetry (Fernandes et al., 2003; Rodriguez et al., 2003). Nevertheless, in the [O.sub.2] uptake kinetics related literature, studies that aimed to characterize it in human non-constant load extreme intensity exercises are very scarce. Moreover, among these studies, only Rodriguez and Mader (2003), Rodriguez et al. (2003), and Silva et al. (2006) implemented a swimming effort at intensities similar to our protocol.

Considering the total sample, V[O.sub.2]peak ranged from 60.2 to 81.8 ml x [kg.sup.-1] x [min.sup.-1], which is in accordance with recently reported data obtained in trained male competitive swimmers performing during swimming in pool conditions (Fernandes et al., 2008; Figueiredo et al., 2011; Reis et al., 2010; Rodriguez and Mader, 2003; Rodriguez et al., 2003; Silva et al., 2006).

[FIGURE 2 OMITTED]

Symmetry between the on- and off-transient phases: Since symmetry is an essential quality of V[O.sub.2] kinetic dynamics viewed as a first-order reaction kinetics (Rossiter et al., 2005), it was a focus of interest in the present study. The on/off symmetry of the fast components has been observed for the moderate intensity exercise domain performed in cycle ergometer (Paterson and Whipp, 1991; 0zyener et al., 2001; Scheuermann et al., 2001) and treadmill running (Kilding et al., 2006). For the heavy intensity exercise, an asymmetry in the V[O.sub.2] dynamics has been reported, describing an on-fast component and an off-fast and off-slow components at cycle ergometer (0zyener et al., 2001) and knee extensor exercise (Rossiter et al., 2002). This asymmetry was also reported for severe exercise intensity, namely in indoor running (Dupond et al., 2010) and cycle ergometer (Ozyener et al., 2001). In contrast, in the present study the on- and off-transient phases were symmetrical, once they were adequately fitted by a single exponential function, compared to the double exponential one, and no slow component for the V[O.sub.2] response was developed (see Figure 1). Nonetheless the above referred studies, the symmetry observed in the present study can be explained by the implementation of a non-constant load, and to the greater exercise intensity. As expected, we observed only an on-fast component, since the non-constant load at freely-chosen maximal race pace induced an exponential rise in V[O.sub.2] kinetics that unable the development of a V[O.sub.2] slow component; this fact was previously mentioned but only for ergometer exercise (Burnley and Jones, 2007; Whipp, 1994).

On/off kinetic parameters: Although an on/off symmetry in the V[O.sub.2] kinetic response was observed in this extreme intensity exercise lasting 2.7 min on average, differences between the V[O.sub.2] on- and off-transient kinetic parameters were observed. In fact, greater [A.sub.off] and [[tau].sub.off] values are reported. This last parameter is a major focus of interest in the V[O.sub.2] kinetic related literature, once it is a determinant factor in V[O.sub.2] dynamics. A longer [[tau].sub.off] value, as observed in this study, concur with previous data obtained in the heavy exercise domain (Cleuziou et al., 2004; Yano et al., 2007); however, other studies reported the opposite behavior for the same exercise intensity (Engelen et al., 1996; Ozyener et al., 2001; Scheuermann et al., 2001), as well as for the moderate domain (Patterson and Whipp, 1991). At the severe exercise intensity, Billat et al. (2002) and 0zyener et al. (2001) reported no differences in t regarding on and off fast periods. In addition, the obtained [[tau].sub.off] mean value was greater than the results reported in the literature for both moderate (Cleuziou et al., 2004; Kilding et al., 2006; Rossiter et al., 2002; Takayoshi et al., 2003), heavy (Rossiter et al., 2002) and severe intensities (Perrey et al., 2002).

However, as suggest, when we compared our data with studies using a double exponential fitting approach, [[tau].sub.off] was shorter comparing to [[tau].sub.off] of the slow component during heavy (Cleuziou et al., 2004) and severe intensity exercise (Dupond et al., 2010). As previously stated, the present study reported a symmetry on the on/off V[O.sub.2] kinetic response; however differences between the on- and off- V[O.sub.2] kinetic related parameters were found.

In fact, V[O.sub.2] kinetics is influenced by endurance training, being reported a faster V[O.sub.2] on-kinetics in trained subjects involved both in cross-sectional and longitudinal studies (Casaburi et al., 1987; Koppo et al., 2004; Murias et al., 2010; Phillips et al., 1995). Indeed, training seems to change the muscle fiber-type characteristics, mitochondrial density, oxidative enzyme activity, oxygen availability, capillary density and muscle perfusion (Koppo et al., 2004), existing evident differences between trained and untrained subjects. Although this study did not have the intention to investigate this phenomenon, the mean swimming speed was very high since the onset of the effort, which may induced a faster increase in ATP requirements, and a fast lactate accumulation, once a pattern of type I/II muscle fiber contribution seems to be established without delay (Cunningham et al., 2000). These facts (and being the off-set fast component explained by the restore of [O.sub.2] in blood and in muscle, a significant lactate removal, and by the resynthesis of ATP and PCr) may induce discernible slower responses during the recovery period. Hence, the oxygen debt must be larger than the oxygen deficit, i.e., the post-exercise V[O.sub.2] quantitatively did not match the [O.sub.2] deficit (Yano et al., 2007). In fact, since different pacing strategies were adopted during the maximal 200-m, different V[O.sub.2] on kinetics may occurred, which influenced the V[O.sub.2] response in the recovery period. This is a limitation of the current study comparing to constant pace researches.

Regarding the V[O.sub.2] amplitude, the greater observed [A.sub.off] mean value (comparing to [A.sub.on]) is not in accordance with the results reported for moderate and heavy intensities (Cleuziou et al., 2004), and for the severe intensity exercise (Perrey et al., 2002), that showed no significant differences between the [A.sub.on] and [A.sub.off] mean values. In our study, the greater values of [A.sub.off] may be a result of the extreme exercise intensity in which our study was conducted, different modeling procedures that were used, as also mode of exercise performed. At this exercise intensity, in which highest work rates are observed, the V[O.sub.2] mean value is high even until the end of the effort. Once the [A.sub.off] represents the difference between the V[O.sub.2] at the end of the exercise and the steady state V[O.sub.2], the greater [A.sub.off] mean value seems justified.

Once the [TD.sub.off] was assumed to be zero, in result of the sudden and instantaneous diminishing of V[O.sub.2], comparisons with previously reported data obtained for the moderate (Cleuziou et al., 2004) and heavy intensities domains (Billat et al., 2002) are difficult to establish. However, Takayoshi et al. (2003) reported low [TD.sub.off] mean values (1, 2 s) for the moderate exercise intensity domain. Moreover, and contrasting the results of the present study, Perrey et al. (2002) found no differences between the [TD.sub.on] and [TD.sub.off] mean values at severe intensity.

Relationship between V[O.sub.2] kinetics on/off-transient phases and performance: The observed direct relationship between [[tau].sub.off] and [200.sub.speed] evidences that the swimmers who performed a faster 200-m, needed more time to attained a V[O.sub.2] steady state in the off-transient phase; in addition, these swimmers presented greater V[O.sub.2]peak and [A.sub.on] mean values. These facts seem to evidence one more time that the very high swimming speed just after the beginning of the effort led to greater V[O.sub.2]peak and [A.sub.on] mean values, increasing both the need for a higher energy supply and the accumulation of fatigue-related metabolites, slowing the recovery phase. Indeed, the 200-m performance is strongly related to the [[tau].sub.off], which seems to be also a good predictor of V[O.sub.2]peak and [A.sub.on]. However, these data should be seen with precaution, once other factors might explain the performance variability in this specific distance.

Conclusion

No slow component for the V[O.sub.2] off-kinetics was developed in the all-out 200-m swims, and the on and off-transient phases were symmetrical once they were adequately fitted by a single-exponential function. However, [A.sub.off] and [[tau].sub.off] mean values were greater comparing to the respective on-transients parameters. The V[O.sub.2]peak and [200.sub.speed] mean values positively correlated with [[tau].sub.off], as this with [A.sub.on], not being observed any more correlations between any of the studied on/off-transient kinetic parameters. Accepting that the overall understanding of the V[O.sub.2] kinetics implies the address of other research areas, future experiments are welcome to understand the underlying mechanism regarding this V[O.sub.2] dynamic behavior.

Key points

* The V[O.sub.2] 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 V[O.sub.2] decline during the recovery period may be due to not only the magnitude of oxygen debt but also the V[O.sub.2]peak obtained during the effort period.

Acknowledgments

This study was supported by grant: PTDC/DES/101224/2008 (FC0MP01-0124-FEDER-009577).

Received: 18 April 2011 / Accepted: 20 July 2011 / Published (online): 01 September 2011

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Ana SOUSA

Employment

FCT research assistant. Sport Sciences PhD student. Collaborator of the Centre of Research, Education, Innovation and Intervention in Sport.

Degree

MSc on Sport Sciences.

Research interests

Physiology applied to swimming, swimming training.

E-mail: sousa.acm@gmail.com

Pedro FIGUEIREDO

Employment

FCT research assistant. Sport Sciences PhD student. Collaborator of the Centre of Research, Education, Innovation and Intervention in Sport.

Degree

Graduation on Sport Sciences.

Research interests

Biomechanics and physiology applied to swimming, triathlon training.

E-mail: spafg@vodafone.pt

Kari KESKINEN

Employment

Executive Director at Finnish Society of Sport Sciences. Professor, Researcher, Lecturer at University of Jyvaskyla. Degree

PhD

Research interests

Physiological evaluation applied to swimming.

E-mail: kari.keskinen@lts.fi

Ferran RODRIGUEZ

Employment

Medical Doctor at the Department of Health and Applied Sciences of the University of Barcelona.

Degree

PhD, MD

Research interests

Physiological evaluation applied to swimming.

E-mail: farodriguez@gencat.cat

Leandro MACHADO

Employment

Auxiliary Professor at the Porto University. Member of Centre of Research, Education, Innovation and Intervention in Sport.

Degree

PhD

Research interests

Mathematical approach applied to swimming.

E-mail: lmachado@fade.up.pt

Joao Paulo VILAS-BOAS

Employment

Full Professor, Head of the Biomechanics Lab at the Porto University. Member of the Scientific Committee of Centre of Research, Education, Innovation and Intervention in Sport.

Degree

PhD on Sport Sciences.

Research interests

Biomechanics, exercise physiology applied to swimming.

E-mail: jpvb@fade.up.pt

Ricardo J. FERNANDES

Employment

Auxiliary Professor, Head of the Swimming Department at the Porto University. Member of Centre of Research, Education, Innovation and Intervention in Sport.

Degree

PhD on Sport Sciences.

Research interests

Swimming biophysical characterization specially centered on the availability and use of energy.

E-mail: ricfer@fade.up.pt

Ana Sousa (1), Pedro Figueiredo (1), Kari L. Keskinen (2), Ferran A. Rodriguez (3), Leandro Machado (1), Joao P. Vilas-Boas (1), Ricardo J. Fernandes (1) [mail]

(1) Centre of Research, Education, Innovation and Intervention in Sport, Faculty of Sport, University of Porto, Portugal,

(2) Finnish Society of Sport Sciences, Finland, 3 National Institute of Physical Education of Catalonia (INEFC), University of Barcelona, Barcelona, Spain

[mail] Ricardo J. Fernandes

Faculty of Sport, University of Porto, Rua Placido Costa, 91, 4200, Portugal
Table 1. Individual, mean ([+ or -] SD) values, coefficient of
variation and confidence interval for mean for [200.sub.speed],
V[0.sub.2peak], [A.sub.on], [TD.sub.on] and [[tau].sub.on],
[A.sub.off] and [[tau].sub.off] in the 200-m maximal effort and
recovery period.

     Swimmer         [200.sub.speed]      V[O.sub.2peak]
                     (m x [s.sup.-1])   (mL x [kg.sup.-1] x
                                           [min.sup.-1])

        #1                 1.40                68.4
        #2                 1.36                60.2
        #3                 1.44                67.4
        #4                 1.42                70.7
        #5                 1.49                81.8
        #6                 1.42                70.1
        #7                 1.42                63.7
        #8                 1.47                69.0

Mean ([+ or -] SD)      1.42 (.04)          69.0 (6.3)
     CV mean              2.81%                9.13%
     CI mean            1.39-1.46            63.7-74.3

     Swimmer             [A.sub.on]        [TD.sub.on]   [[tau].sub.on]
                     (mL x [kg.sup.-1] x       (s)            (s)
                        [min.sup.-1])

        #1                  49.6              10.00           6.21
        #2                  38.6              4.99           12.04
        #3                  44.9              3.98           13.28
        #4                  44.5              4.99            9.31
        #5                  52.0              5.00           12.43
        #6                  45.4              4.99           11.56
        #7                  46.9              4.99            9.17
        #8                  50.2              4.99           13.41

Mean ([+ or -] SD)       46.5 (4.2)        5.49 (1.85)    10.92 (2.49)
     CV mean                9.05%            33.69%          22.84%
     CI mean              43.0-50.0         3.93-7.04      8.84-13.01

     Swimmer            [A.sub.off]      [[tau].sub.off]
                     (mL x [kg.sup.-1]         (s)
                      x [min.sup.-1])

        #1                 54.4               62.22
        #2                 41.2               49.38
        #3                 41.5               55.14
        #4                 54.8               73.13
        #5                 50.1               94.04
        #6                 49.3               84.36
        #7                 42.2               73.90
        #8                 62.3               86.23

Mean ([+ or -] SD)      49.5 (7.56)       72.30(15.75)
     CV mean              15.27%             21.78%
     CI mean             43.2-55.8         59.13-85.46

[200.sub.speed] = mean swimming speed of the 200-m; V[O.sub.2peak] =
peak oxygen uptake; [A.sub.on] = amplitude of the fast component in
the 200-m maximal effort; [TD.sub.on] = time of the onset of the fast
component in the 200-m maximal effort; [[tau].sub.on] = time constant
of the fast component in the 200-m maximal effort; [A.sub.off] =
amplitude of the fast component in the 200-m recovery period;
[[tau].sub.off] = time constant of the fast component in the 200-m
recovery period; CV = coefficient of variation; CI = confidence
interval.
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Article Details
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Title Annotation:Research article
Author:Sousa, Ana; Figueiredo, Pedro; Keskinen, Kari L.; Rodriguez, Ferran A.; Machado, Leandro; Vilas-Boas
Publication:Journal of Sports Science and Medicine
Article Type:Report
Geographic Code:4EUSP
Date:Sep 1, 2011
Words:5800
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