Oxygen uptake kinetics at moderate and extreme swimming intensities

Abstracts

INTRODUCTION: Traditionally, studies regarding oxygen consumption kinetics are conducted at lower intensities, very different from those in which the sports performance occurs. OBJECTIVE: Knowing that the magnitude of this physiological parameter depends on the intensity in which the effort occurs, it was intended with this study compare the oxygen consumption kinetics in the 200 m front crawl at two different intensities: moderate and extreme. METHODS: Ten international male level swimmers two separate tests by 24h: (i) progressive and intermittent protocol of 7 x 200 m, with 30 seconds intervals and with increments of 0.05m.s-1, to determine the anaerobic threshold correspondent step; and, (ii) 200 m at maximal velocity: in both expiratory gases were continuously collected breath-by-breath. RESULTS: Significant differences were obtained between amplitude and time constant determine in the 200 m at extreme and moderate intensities, respectively (38,53 ± 5,30 ml. kg-1.min-1 versus 26,32 ± 9,73 ml. kg-1.min-1 e 13,21 ± 5,86 s versus 18,89 ± 6,53 s (p ≤ 0,05). No differences were found in time delay (9,47 ± 6,42 s versus 12,36 ± 6,62 s, at extreme and moderate intensity, respectively (p ≤ 0.05). A negative correlation between time delay and time constant at the moderate intensity was reported (r = - 0,74, p ≤ 0,05). CONCLUSIONS: Both intensities were well described by double-exponential fittings, and there were significant differences between them in terms of amplitude and time constant.

swimming; VO2 kinetics; moderate intensity; extreme intensity

INTRODUÇÃO: Tradicionalmente, os estudos da cinética do consumo de oxigênio são conduzidos a intensidades de exercício baixas, bem distintas daquelas em que o desempenho desportivo acontece. OBJETIVO: Considerando que a magnitude da cinética deste parâmetro fisiológico depende da intensidade a que o esforço é realizado, pretendeu-se com este trabalho comparar a cinética do consumo de oxigênio em 200 m crowl nadados a duas intensidades distintas: moderada e extrema. MÉTODOS: Dez nadadores do sexo masculino, de nível internacional, realizaram dois testes separados: (i) protocolo progressivo e intervalado de7 x200 m, com 30 segundos de intervalo e incrementos de 0,05 m.s-1 para determinação do patamar correspondente ao limiar anaeróbio; e (ii) 200 m à máxima velocidade. Em ambos, realizou-se uma recolha contínua de gases expirados respiração-a-respiração. RESULTADOS: Diferenças significativas foram obtidas na amplitude e constante temporal determinadas nos 200 m nadados à intensidade extrema e moderada, respectivamente: 38,53 ± 5,30 versus 26,32 ± 9,73 ml. kg-1.min-1 e 13,21 ± 5,86 versus 18,89 ± 6,53 s (p ≤ 0,05). Não foram encontradas diferenças no atraso temporal (9,47 ± 6,42 versus 12,36 ± 6,62 s (p ≤ 0,05), à intensidade extrema e moderada, respectivamente. O atraso temporal correlacionou-se negativamente com a constante temporal à intensidade moderada (r = -0,74, p ≤ 0,05). CONCLUSÕES: Ambas as intensidades estudadas foram bem descritas por aproximações mono-exponenciais, tendo-se verificado diferenças significativas entre as mesmas no que concerne à amplitude e constante temporal.

natação; cinética do consumo de oxigênio; intensidade moderada; intensidade extrema

ORIGINAL ARTICLE

EXERCISE AND SPORTS MEDICINE CLINIC

Oxygen uptake kinetics at moderate and extreme swimming intensities

Ana Sousa^I; Kelly de Jesus^I; Pedro Figueiredo^I; João Paulo Vilas-Boas^I,II; Ricardo J. Fernandes^I,II

^ICentre of Research, Education, Innovation and Intervention in Sport, Faculty of Sport, University of Porto, Portugal

^IILaboratory of Biomechanics LABIOMEP, University of Porto, Portugal

Mailing address

ABSTRACT

INTRODUCTION: Traditionally, studies regarding oxygen consumption kinetics are conducted at lower intensities, very different from those in which the sports performance occurs.

OBJECTIVE: Knowing that the magnitude of this physiological parameter depends on the intensity in which the effort occurs, it was intended with this study to compare the oxygen consumption kinetics in the 200 m front crawl at two different intensities: moderate and extreme.

METHODS: Ten male swimmers of international level performed two tests separated by 24h: (i) progressive and intermittent protocol of 7 x 200 m, with 30 seconds intervals and with increments of 0.05m.s^-1, to determine the anaerobic threshold correspondent step; and, (ii) 200 m at maximal velocity, in both expiratory gases were continuously collected breath-by-breath.

RESULTS: Significant differences were obtained between amplitude and time constant determined in the 200 m at extreme and moderate intensities, respectively (38.53 ± 5.30 ml. kg^-1.min^-1versus 26.32 ± 9.73 ml. kg^-1.min^-1 and 13.21 ± 5.86 s versus 18.89 ± 6.53 s (p ≤ 0.05). No differences were found in time delay (9.47 ± 6.42 s versus 12.36 ± 6.62 s, at extreme and moderate intensity, respectively (p ≤ 0.05). A negative correlation between time delay and time constant at the moderate intensity was reported (r = - 0.74, p ≤ 0.05).

CONCLUSIONS: Both intensities were well described by double-exponential fittings and there were significant differences between them in terms of amplitude and time constant.

Keywords: swimming, VO₂ kinetics, moderate intensity, extreme intensity.

INTRODUCTION

The magnitude and nature of the adjustment of the oxygen consumption (VO₂) at the beginning of any physical exercise strongly depends on the intensity at which the effort is performed¹. In fact, at moderate intensities, where exercise is performed below the anaerobic threshold, the VO₂ reaches a quick balance state after a single growth phase, which is named fast component². At high intensity though, for example, above the anaerobic threshold, the VO₂ kinetics reveals a new phase – the slow component –, which, when appearing after the fast component, delays the onset of the balance state of VO₂³. At severe intensities, where exercise is performed significantly above the anaerobic threshold, the VO₂ and blood lactate values ([La-]) are not able to stabilize, and therefore, the VO₂ kinetics exposes two components (fast and slow), finishing the exercise before it is possible to obtain a balance state⁴. Although it has been described very recently, the extreme intensity domain, being performed at intensity above maximal oxygen consumption (VO_2max), reflects the intensity at which the majority of the competitive efforts occur². However, few studies have been conducted in this domain, being almost unexplored in swimming, especially at higher intensities. The aim of the present work is to analyze and compare the VO₂ kinetics at two distinct swimming intensities, in conditions as close as possible to the ones obtained during competition: (i) moderate intensity, analyzing 200 m crawl at intensity corresponding to the individual anaerobic threshold – lan_ind); and (ii) extreme intensity, evaluating 200 m crawl swam at maximum intensity.

METHODS

Sample

10 male swimmers of international level participated in this study. The individual and mean (± sd) values of their main physical characteristics and of competitive swimming practice are presented in table 1. The body weight and fat mass values were determined through bioelectrical impedance (Tanita TBF 305, Tokyo, Japan). All subjects were previously informed about the details of the experimental protocol before the data collection, having offered their written consent for the participation. The protocol was approved by the ethics committee of the local Institution.

Instruments and procedures

All experimental sessions occurred in an indoors 25 m acclimatized swimming pool (27ºC), with relative humidity of 45%. Each subject performed two distinct protocols in the crawl style, and an interval of 24 hours between them was respected. A progressive and interval protocol of 7 x 200 m, with 30 seconds of interval with increments of 0.05m.s-1 between each step^5,6. The velocity of the last step was determined according to the performance hypothetically reached at that time at 400 m crawl, subtracting later to six intensity thresholds; swimming velocity was controlled with a light pacer (TAR 1.1, GBK – electronics, Aveiro, Portugal), placed in the bottom of the pool. This test was used to determine the 200 m which was closer (or coinciding) with the velocity corresponding to the lan_ind., 24 hours after that, the 200 m crawl at maximum velocity was performed⁷. In both protocols, the starts were performed from the water, and the swimmers were told to perform open laps, always to the same side and without gliding. The VO₂ was measured through continuous expired gas collection breath-by-breath through a portable gas analyzer (K4b², Cosmed, Italy), which was connected to the swimmer through a respiratory tube and valve considered suitable for ventilatory gas parameters collection in swimming situations⁸. All that experimental equipment was lifted 2 m above the water surface on a steel cable, which made it possible to follow the swimmer along the pool, minimizing discomfort to the swimmer's movements (figure 1).

In order to minimize the noise resulting from the gas collection breath-by-breath, data were then edited to exclude faulty breathing (e.g. coughing), which do not realistically represent the subjacent kinetics, being only considered the values comprised between the mean ± four standard deviations⁹. Subsequently, the data obtained breath-by-breath were softened through a movable mean of three breaths¹⁰ and recorded in mean periods of five seconds¹¹, increasing the validity of the estimated parameter. Capillary blood was collected from the earlobe and used to determine the [La^-] using a portable analyzer (Lactate Pro analyzer, Arcay, Inc). The collections occurred before each protocol, during the recovery periods (incremental protocol) and at the end of them (at minutes 1, 3, 5 and 7 of recovery). The [La^-] enabled the determination of lan_ind, in the incremental protocol through the [La^-] curve modeling versus velocity, assuming it was the interception point of the best adjustment of linear and exponential regressions used for determination of the exact point of the beginning of exponential increase of [La^-]^12,13. In all swimmers from the sample, the inflexion point of the [La^-] occurred at the 4th step of the incremental protocol. Heart rate values were continuously monitored (at each five seconds) through a monitor system (Polar Vantage NV, Polar Electro Oy, Kempele, Finland).

In order to analyze the VO₂ kinetics, the curves considered (from the 200m corresponding to the lan_ind and from 200 m at maximal velocity) were modeled considering a mono-exponential fitting (equation 1):

Where t is the time (s), V_b is the VO₂ value at the beginning of the exercise (ml.kg^-1.min^-1), A is the amplitude of the fast component (ml.kg^-1.min^-1), TD is time of beginning of the fast component (s) and t is the time constant of the fast component (s), i.e., the time needed to reach 63% of the plateau of this phase.

Additionally, the VO₂ curves corresponding to the Ian_ind were also modeled considering two exponential phases (equation 2 – bi-exponential):

Where t is the time (s), V_b is the VO₂ value at the beginning of the exercise (ml.kg^-1.min^-1), A₁ and A₂ are the amplitude of the fast and slow components (ml.kg^-1.min^-1), TD₁ and TD₂ are the times of the beginning of the fast and slow components (s) and t₁ and t₂ are the time constants of the fast and slow components (s), respectively. The linear method of the minimum squares was implemented in the Matlab program for the adjustment of this function to the VO₂ data.

Statistical Analysis

The mean values (± standard deviation) for the descriptive analysis were obtained for all the variables of the study, for the total sample and each subject, and normality of its distribution was verified through the Shapiro-Wilk test. The SPSS program (linear regression, and the T-Test of repeated measures) was used for the inferential statistical analysis, and significance level was established at 0.05. The F-Test was used for comparison of the monoexponential and bi-exponential fitting of the VO₂ curves corresponding to the lan_ind. swimming intensity.

RESULTS

The F-Test (p = 0.91) presented the homogeneity of the variance of the monoexponential and bi-exponential models used to analyze the 200 m crawl performed at the intensity corresponding to the lan_ind, which was confirmed by the equality of mean values through the T-Test (p = 0.97). Thus, in the present study the VO₂ kinetics at moderate and extreme intensities seem to be well-described by a monoexponential function, not being positive to use a bi-exponential function. Figure 2 presents two illustration curves of the VO₂ kinetics of one swimmer, in the 200 m corresponding to the lan_ind, and in the 200 m performed at maximum intensity.

The mean values (± sd) of A_lan, A₂₀₀, t_lan, t₂₀₀, TD_lan and TD₂₀₀, at moderate and extreme intensities, are presented in table 2.

Statistically significant differences were obtained in two kinetic parameters (amplitude and time constant) between the 200 m performed at the lan_ind and maximal velocity intensities. Additionally, negative correlations were found between TD_lan and t_lan (R = -0.74, p = 0.01, figure 3). Nonetheless, further significant relations were not found in the remaining studied parameters.

DISCUSSION

The aim of the present study was to assess and compare the VO₂ kinetics in 200 m crawl performed at two distinct swimming intensities: moderate (corresponding to the lan_ind) and extreme (at maximal intensity). Since these two intensities are considered very important in the swimming training, as they are used for the development of the aerobic and anaerobic capacities, respectively, it seems crucial to provide better understanding on the VO₂ kinetic parameters. The literature has highlighted the study of low and moderate effort intensities, while studies concerning higher intensities are scarcer, which are representative of the swimming rhythm used during competition. Moreover, the existing studies occurred at unspecific and/or laboratory evaluation conditions (e.g. cycling ergometer and treadmills), compromising hence the validity and applicability of their results. Concerning swimming, only Rodríguez et al.¹⁴, Rodríguez et al.¹⁵ and Sousa et al.⁷ carried out studies at high intensities and at conditions as close as possible to the real swimming conditions, and there are no comparative studies between intensity domains.

Exercise intensity below the Ian_ind is characterized by the presence of three distinct phases: cardiodynamic, fast and the VO₂ stabilization which occurs three minutes after the beginning of the exercise¹⁶. The intensity immediately above the lan_ind presents an additional phase (slow component), which delays the onset in the VO₂ stabilization, appearing approximately 10 minutes after the beginning of the effort². However, being the upper boundary of the moderate intensity and, consecutively, the lower one in the high intensity domain, the lan_ind is an intensity little studied concerning the VO₂ kinetics. However, Ozyener et al.⁹ refer that moderate intensities are well-described by monoexponential fittings, instead of the high intensities (high and sever intensity domains) which are better characterized by bi-exponential fittings.

In the present study, and considering the F-Test values, it was verified that the intensity corresponding to the lan_ind, _the VO₂ kinetics will be possibly described considering the existence of a single phase (fast component) and, consequently, the use of a bi-exponential fitting becomes unnecessary. Although no study has been carried out at this specific intensity, other ones conducted at the moderate intensity domain presented monoexponential fitting in the VO₂ kinetics^17-21. Concerning extreme intensity, monoexponential fittings were previously defined as being more positive for this intensity domain⁷.

Concerning the kinetic parameters, we verified that they are significantly different between the two exercise intensities studied, especially regarding amplitude and time constant. Thus, higher values of these two parameters were obtained in the 200 m crawl performed at maximal velocity, contrary to the time delay whose mean values were higher at the intensity corresponding to the lan_ind. The amplitude values corroborate the ones presented in the literature, either for the moderate ^3,17,19,21 or for the extreme domain⁷, where only the later was carried out with swimming. The tendency for higher values of amplitude in the extreme domain supports the literature carried out in cycle ergometer^18,19,21 and in domains of high intensity²². These differences are due to the higher values of VO₂ reached in the extreme domain (higher oxygen demand), since as the effort intensity increases, the amplitude gain is higher. This fact is well-explained in figure 2, where the higher VO₂ values reached at the end of the exercise can be observed.

Despite this, higher VO₂ values are also observed at the beginning of the moderate effort, comparatively to the effort performed at extreme intensity. Such fact is due to the previous performance of the 200 m crawl steps included in the protocol used (cf. instrument and procedures section) and that, despite being performed at low intensity, induced an increase in the VO₂ baseline values at the beginning of the following step. However, studies conducted refer that only previous exercise of high intensity conditions and influences the following efforts, namely slow component VO₂^23,24 kinetics. Thus, it seems that the existence of low intensity plateaus preceding the effort corresponding to the lan_ind did not influence the respective VO₂ kinetics to lan_ind. Significant differences went to the time constant, being higher at the intensity corresponding to the lan_ind, clashing hence with some studies which refer the constancy of this parameter along the different intensities^17,19,21. However, it should be mentioned that the later ones were performed in cycle ergometer and comparing moderate to high intensity and/or severe domains.

In spite of this information, the values of the time constant observed for the 200 m crawl performed at maximal velocity are lower than the ones reported in the literature^14,15, especially for the 100 and 400 m distances, but similar to the ones by Sousa et al.⁷ for the same distance. Regarding the intensity corresponding to the lan_ind, the values presented corroborate the ones reported in the literature for efforts performed in cycle ergometer^17-21. In the present study, the fact the time constant is not similar between the two intensities seems to be due to the extreme intensity at which the 200 m crawl were performed. Therefore, and since the value of the time constant describes the adaptation profile of the cardiovascular and muscular systems at the intensity of the performed effort²⁵, the sudden and exponential need of VO₂ to higher intensities (figure 2) will be able to explain the lower values of this parameter.

The time delay was the only kinetic parameter where significant differences have not been verified between the two studied intensities, corroborating the studies which compare the moderate and high exercise domains¹⁷ and moderate and severe domains¹⁹. However, Pringle et al.²¹ showed that this parameter ranges between the moderate, high and severe domains. Although the mean values found in our study are lower than the ones found in the literature for the moderate domain^17,19,21, the values corresponding to the extreme domain agree with the only study conducted in the swimming environment for the 200 m distance⁷. In the moderate domain, the differences found may be due to the fact the studies mentioned have been conducted in different sports modalities.

The negative correlation observed between the delay and time constant in the 200 m crawl performed at lan_ind intensities has not been previously reported in the literature; nevertheless, in the present sample the swimmers, whose fast component of VO₂ started earlier (shorter time delay), were those who also needed more time (longer time constant) until they reached stabilization in the VO₂ consumption. Thus, the sports performance level of our sample (high level) as well as its specialty (sprinters) seem to be two factors which explain the correlations reported here.

CONCLUSION

Both were well described by mono exponential fittings and significant differences have been verified between them concerning amplitude and time constant. Thus, higher values of these two kinetic parameters have been obtained in 200 m crawl performed at maximum velocity, contrary to the timed delay whose mean was higher at the intensity corresponding to the lan_ind. Additionally, negative correlations have been obtained between TD_lan and t_lan.

ACKNOWLEDGEMENTS

Science and Technology Foundation (PTDC/DES/101224/2008; SFRH/BD/72610/2010).

All authors have declared there is not any potential conflict of interests concerning this article.

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Publication Dates

• Publication in this collection
  19 Aug 2013
• Date of issue
  June 2013