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Aerobic endurance measurement by respiratory exchange ratio during a cycle ergometer graded exercise test.

INTRODUCTION

The maximal lactate steady state (MLSS) is considered the "gold standard" procedure in the assessment of aerobic endurance (2,3). However, there are some disadvantages to the assessment of MLSS in sports teams. Aside from the cost of the test, there is the requirement for individuals to complete 3 to 6 constant-load exercise bouts on separate days. Thus, MLSS has been used to validate other procedures of endurance capacity assessment (1,5,7,13). Researchers have validated procedures that estimate MLSS intensity using only a single exercise session. Between these procedures, blood lactate responses (e.g., lactate threshold, lactate minimum test, and others) (2,5,13) and pulmonary parameters such as respiratory compensation point (RCP) and ventilatory threshold (2,11,14,17) have been used. Although the blood lactate response is effective in estimating MLSS intensity, the use of non-invasive procedures is generally better received by the volunteers.

The exercise intensities below and at RCP represents a physiological steady state (17). It is important to point out that the RCP represents the highest exercise intensity in which the respiratory system maintains a physiological steady state (17). In this exercise intensity, the value of the respiratory exchange ratio (RER) is approximately 1.00. Thus, exercises performed at intensities above the RCP (i.e., RER > 1.00) leads to hyperventilation and a higher production of carbon dioxide (VC[O.sub.2]). These responses occur due to the buffering of excess hydrogen released by the muscle during anaerobic metabolism. This process is possible due to the bicarbonate buffering system. In this system, carbon dioxide (C[O.sub.2]) combines with water to form carbonic acid (H2CO3), which in turn dissociates to form hydrogen ion and bicarbonate (HC[O.sub.3.sup.-]) as shown in the reactions below:

C[O.sub.2] + [H.sub.2]0 [??] [H.sub.2]C[0.sub.3] [??] HC[O.sup.-.sub.3] + [H.sup.+]

Dickstein and colleagues (4) reported that the intensity corresponding to the RER (iRER) = 1.00 could be use to predict anaerobic threshold (17), thus indicating the onset of lactic acidosis. In addition, Solberg et al. (16) found that iRER = 1.00 could be used as a good predictor of the exercise intensity in which blood lactate concentration was 1.5 mmol x [L.sup.-1] above the mean blood lactate between the rest and the first load. However, both Dickstein et al. (4) and Solberg et al. (16) compared the iRER = 1.00 with the onset lactic acidosis point (classified as the first increase of the blood lactate concentration (11) and characterized as the aerobic threshold intensity) that does not represent the intensity of aerobic endurance.

Laplaud and Menier (9) verified that the iRER = 1.00 presented reproducibility in a cycle ergometer ram test. They did not find significant differences comparing this intensity with the intensity corresponding to the second ventilatory threshold (V[T.sub.2]) and with the intensity corresponding to the blood lactate concentration of 4.0 mmol x [L.sup.-1]. However, the correlation coefficients between these parameters were not presented in the mentioned study (9). In subsequent studies, the same research group observed that iRER = 1.00 was sensitive to systematic training in basketball players (8) and was able to estimate the MLSS intensity (7).

The use of iRER = 1.00 seems to be a fast and non-invasive procedure that allows for the estimation of aerobic endurance using a single exercise session. To better understand this thinking, it is necessary to compare the iRER = 1.00 with other procedures that estimate aerobic endurance intensity using blood lactate and respiratory responses in single exercise sessions. In addition, to validating the iRER = 1.00 as an aerobic endurance parameter, the use of analysis of association and agreement are necessary. Thus, the purpose of this study was to verify that the use of intensity at the respiratory exchange rate (RER) value of 1.00 (iRER = 1.00) can be used to estimate aerobic endurance during a cycle ergometer graded exercise test. The steps towards verification depend on: (a) comparing the iRER = 1.00 value with anaerobic threshold at the abrupt lactate increase and the onset blood lactate accumulation; and (b) determining the correlation and agreement of the iRER = 1.00 with these procedures.

METHODS

Subjects

Twenty-five healthy and moderately active male subjects (age 22 [+ or -] 1 yrs; height 176.2 [+ or -] 0.9 cm; body weight of 78.1 [+ or -] 2.9 kg) volunteered to participate in this study. The sample size resulted in a statistical power of 100% to analyze comparisons between means. All subjects were verbally informed of the risks and benefits of the study procedures and signed an informed consent before their inclusion in the study. All procedures were approved by the Ethics Committee of the Federal University of Mato Grosso do Sul/Brazil, and were conducted in accordance with the Declaration of Helsinki.

Procedures

To determine the iRER = 1.00, RCP, anaerobic threshold at abrupt lactate increase, and anaerobic threshold corresponding to 3.5 mmol x [L.sup.-1] lactate concentration, the subjects performed a maximal graded exercise test (GXT) on a mechanically braked cycle ergometer (Biotec 2100, Cefise, Brazil). Prior to testing, the subjects performed a warm-up lasting 8 min at an intensity corresponding to 70 W at a cadence of 70 rpm. The cadence of 70 rpm was also used in the GXT, which was started 5 min after the warm-up. The GXT consisted of 70 W of initial workload that was increased by 17.5 W at each stage of 2 min until voluntary exhaustion or inability to keep pace with the cadence for over 5 sec even after substantial verbal encouragement.

Oxygen consumption (V[O.sub.2]), VC[O.sub.2], RER, and ventilation (VE) were collected-by-breath using an automatic gas analyzer True-One 2400 (ParvoMedics, East Sandy, Utah, USA) during the GXT. Heart rate (HR) was measured concomitantly to respiratory measures coupled to an HR belt transmitter (T31, Polar Electro, Kempele, Finland). The gas analyzer was calibrated immediately before each test using known gas samples (3.98% C[O.sub.2] and 16.02% [O.sub.2], Air gas Puritan Medical, USA), while the spirometer was calibrated by a 3-liter syringe (Hans Rudolf, Kansas City, USA). The data collected by the gas analyzer were smoothed to remove the outliers (12) and subsequently interpolated in every 1 sec interval. For analysis of respiratory and ventilatory data at each stage of exercise, the last 20 sec of each effort stage was averaged. An electrochemical analyzer (YSI, Yellow Springs Instruments, Ohio, USA) was used to collect blood samples from the earlobe (25 microliters) immediately after each stage of exercise (without interrupting the test) and at the 5th min and the 7th min at the end of the test to determine blood lactate ([La]). Rate of perceived exertion (RPE) was also measured after each effort stage using the Borg 6-20 scale.

Maximal oxygen consumption (V[O.sub.2] max) corresponded to the highest average V[O.sub.2] over the last 20 sec of the GXT test. The following criteria were also used to determine V[O.sub.2] max: Blood lactate [greater than or equal to] 8.0 mmol x [L.sup.-1]; HR [greater than or equal to] 90% age-predicted HR maximal (220-age); RER [greater than or equal to] 1.10; and V[O.sub.2] plateau (V[O.sub.2] changes [less than or equal to] 2.1 ml x [kg.sup.-1] x [min.sup.-1] between the last two exercise stages), while the maximal aerobic power (MAP) corresponded to the highest power attained in the complete stage during GXT. If the subjects were unable to end the stage, the MAP was calculated using the equation suggested by Kuipers and colleagues (6): [MAP = intensity of the previous stage + ((time of exercise/120) * increment)]

The iRER = 1.00 corresponded to the intensity in which RER was equal to 1.00, RCP corresponded to the intensity in which an increase of both ventilatory equivalents of oxygen ([V.sub.E]/V[O.sub.2]) and carbon dioxide ([V.sub.E]/VC[O.sub.2]) was observed, anaerobic threshold corresponding to the lactate abrupt increase ([AnT.sub.LAC]) was determined using a bi-segmented linear regression, and the intensity of onset blood lactate accumulation ([OBLA.sub.3.5]) corresponded to the intensity of 3.5 mmol x [L.sup.-1] blood lactate. After these measures, the values of V[O.sub.2], HR, [La], and RPE at iRER = 1.00, RCP, [OBLA.sub.3.5] and [AnT.sub.LAC] were also determined.

Statistical Analyses

The data are shown in mean [+ or -] standard error of mean. Initially, the Shapiro-Wilk's test was applied and the normality of the data was confirmed. One-way repeated measures analysis of variance was used to compare the iRER = 1.00 with RCP, [AnT.sub.LAC] and [OBLA.sub.3,5] and to compare the V[O.sub.2], HR, [La], and RPE correspondents at these intensities. In addition, Mauchly's sphericity test was applied to the data and sphericity was assumed when the F test was significant. In case of violation of sphericity, the Greenhouse-Geisser Epsilion correction was used. Analysis was completed by using Bonferroni's multiple comparison tests. The Pearson product-moment correlation coefficient was used to verify the relationship between each parameter and the Bland-Altman plot was used to verify the agreement of the data. In addition to the significance level (P = 0.05), the correlation coefficients were classified as very weak to negligible (0.0 to 0.2), weak (0.2 to 0.4), moderate (0.4 to 0.7), strong (0.7 to 0.9), and very strong (0.9 to 1.0) (15). In all cases, statistical significance was set at P = 0.05.

RESULTS

The subjects' V[O.sub.2] max and MAP measured during the GXT were 43.0 [+ or -] 1.3 ml x [kg.sup.-1] x [min.sup.-1] and 182.7 [+ or -] 6.2 W, respectively. Table 1 shows the intensities of iRER = 1.00, [OBLA.sub.3.5], [AnT.sub.LAC] and RCP, and the V[O.sub.2], V[O.sub.2] at V[O.sub.2] max, HR, HR at HR max, RER, [La], and RPE at these intensities. There were no significant differences for almost all variables, except to RER at [AnT.sub.LAC] that was higher than the RER values at [OBLA.sub.3,5] and RCP.

The iRER = 1.00 was strong and statistically correlated with [AnT.sub.LAC] and [OBLA.sub.3.5], whereas the correlation with RCP intensity was significant and very strong. In addition, the V[O.sub.2] and RPE at iRER = 1.00 were statistically correlated with the same parameters at RCP, [AnT.sub.LAC] and [OBLA.sub.3.5] intensities. In respect to the correlation coefficients, [AnT.sub.LAC] versus intensity at MAP, HR at HR max, and lactate did not present significant correlations.

Figure 1 showns the Bland-Altman plots of iRER = 1.00 with RCP (Figure 1A), [AnT.sub.LAC] (Figure 1B), and [OBLA.sub.3.5] (Figure 1C) intensities. Low bias (residual value of average of difference) and moderate random errors (lower and upper limits) were found, showing good absolute agreement of the iRER = 1.00 with RCP, [AnT.sub.LAC] and [OBLA.sub.3.5] intensities.

[FIGURE 1 OMITTED]

DISCUSSION

The main findings of this study were the similar values between the iRER = 1.00, RCP, [OBLA.sub.3.5] and [AnT.sub.LAC] intensities as well as between the other parameters at these intensities (V[O.sub.2], HR, HR at maximal, RER, [La], and RPE). In addition, our results showed the good agreement of iRER = 1.00 with RCP, [OBLA.sub.3.5] and [AnT.sub.LAC] intensities analyzed by Bland-Altman plots and the significant correlations of iRER = 1.00 with [OBLA.sub.3.5], [AnT.sub.LAC] and RCP intensities and other parameters at these intensities.

The aerobic endurance intensity is widely used to measure the aerobic conditioning in sedentary and trained subjects, and it is used for exercise prescription. Therefore, the development of a procedure that allows for measuring this intensity using a fast and non-invasive test is necessary. Anaerobic threshold intensity is the most common parameter used to measure the aerobic endurance, and it can be estimated by the abrupt increase of the blood lactate (11), by fixed blood lactate values (5,13), and by ventilatory and respiratory responses (RCP) (11,17). However, it is important to point out that in the present study anaerobic threshold was assumed as the same physiological phenomena as the maximal lactate steady state intensity. In the literature, there are several authors using anaerobic threshold to describe different physiological phenomena (17). Therefore, we compared the iRER = 1.00 with RCP, [AnT.sub.LAC] and [OBLA.sub.3.5], which theoretically corresponds to the same physiological phenomena (11).

Our findings are in agreement with Laplaud and colleagues (7,8,9) who reported similar values for iRER = 1.00 with RCP, [AnT.sub.LAC] and [OBLA.sub.3.5] intensities. In the Bland-Altman plots, low average of differences (bias) were observed for iRER = 1.00 and RCP (-3.0 W; -1.6%), [AnT.sub.LAC] (-5.7 W; -4.9[degrees]%) and [OBLA.sub.3.5] (3.0 W; 3.4%). The absolute agreement of the Bland-Altman plot was verified by the mean of difference between two values and values near to zero and represents the higher agreement between two parameters. The acceptation of RER = 1.00 as a good procedure to estimate the aerobic endurance is supported by the similar values observed for MAP, V[O.sub.2], V[O.sub.2] relative to V[O.sub.2] max, HR, HR at HR max, [La], and RPE correspondents to iRER = 1.00, RCP, [OBLA.sub.3.5] and [Ant.sub.LAC]. In addition, to these findings, the RER at RCP was 0.99 [+ or -] 001, 1.02 [+ or -] 001 at [AnT.sub.LAC] and 0.98 [+ or -] 0.01 at [OBLA.sub.3.5], where only the RER at [AnT.sub.LAC] was statistically higher than the other values (Table 1). Laplaud et al. (8) observed in basketball players a significant increase in iRER = 1.00 value after 4.7 months of training, showing that the iRER = 1.00 is also sensitive to aerobic adaptations that occur with systematic training.

It is important to point out that iRER=1.00 corresponds to the intensity that 100% of the energy source is glucose ([C.sub.6][H.sub.12][O.sub.6] + 6[O.sub.2] ? 6[H.sub.2]O + 6C[O.sub.2]; RER = 6C[O.sub.2]/6[O.sub.2] = 1.00) showing the aerobic predominance during this exercise intensity. However, at exercise intensities higher than iRER at 1.00, hyperventilation occurs due to the buffering of excessive [H.sup.+] (17). The intensity at which hyperventilation occurs indicates that the respiratory effort is not efficient and that a physiological steady state is not attained (17).

The agreement of the iRER = 1.00 as an aerobic endurance procedure is supported by the work of Leti and colleagues (10). They reported that the speed at RER = 1.00 did not differ from the speed at MLSS, and both were statistically correlated (r = 0.79). In addition, the V[O.sub.2] at RER = 1.00 did not differ with the V[O.sub.2] at MLSS and V[O.sub.2] at VT2. The RER at VT2 corresponded to 1.00 [+ or -] 0.05, which was equal to iRER = 1.00. However, despite the good absolute agreement between iRER = 1.00 with the other procedures, moderate values of upper and lower limits were found. The random error (lower and upper limits) observed by Bland-Altman plots of iRER = 1.00 can result in modifications around -28.5 to 22.5 W for RCP, -44.6 to 33.3 W to [AnT.sub.LAC] and -30.0 to 36.0 W to [OBLA.sub.3.5]. That is, despite of similar values and significant correlations, individual variations can occur in the aerobic endurance measurement.

The interpretation of an evaluation procedure using only tests that analyze the difference between means and tests of the correlation coefficient can hide a lack of agreement between two or more procedures and, therefore, fail to allow for a robust validity for a new procedure. The inclusion of the agreement analysis (e.g., Bland-Altman plot) represents additional information that confirms the validity of an evaluation procedure, both to absolute agreement (i.e., bias) as well as to individual agreement (i.e., random error).

CONCLUSION

The findings from this study indicate that iRER = 1.00 can be used to estimate aerobic endurance intensity in cycle ergometer exercise.

REFERENCES

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(2.) Beneke, R. Maximal lactate steady state concentration (MLSS): Experimental and modelling approaches. Eur J Appl Physiol. 2003; 88:361-369.

(3.) Beneke R, Von Duvillard SP. Determination of maximal lactate steady state response in selected sports events. Med Sci Sports Exerc. 1996; 28(2):241-246.

(4.) Dickstein K, Barvik S, Aarsland T, Snapinn S, Karlsson J. A comparison of methodologies in detection of the anaerobic threshold. Circulation. 1990; 81(1 Suppl):II38-1146.

(5.) Heck H, Mader A, Hess G, Mucke S, Miller R, Hollmann W. Justification of the 4-mmol/l lactate threshold. Int J Sports Med. 1985; 6(3):117-130.

(6.) Kuipers H, Verstappen FTJ, Keizer HA, Guerten P, Van Kranenburg P. Variability of anaerobic performance in the laboratory and its physiologic correlates. Int J Sports Med. 1985; 6(4):197-201.

(7.) Laplaud D, Guinot M, Favre-juvin A, Flore P. Maximal lactate steady state determination with a single incremental test exercise. Eur J Appl Physiol. 2006; 96(4):446-452.

(8.) Laplaud D, Hug F, Menier R. Training-Induced changes in aerobic aptitudes of professional basketball players. Int J Sports Med. 2004; 25:103-108.

(9.) Laplaud D, Menier R. Reproducibility of the instant of equality of pulmonary gas exchange and its physiological significance. J Sports Med Phys Fitness. 2003; 43(4):437-443.

(10.) Leti T, Mendelson M, Laplaud D, Flore P. Prediction of maximal lactate steady state in runners with an incremental test on the field. J Sports Sci. 2012; 30(6):609-616.

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(12.) Ozyener F, Rossiter HB, Ward SA, Whipp BJ Influence of exercise intensity on the on- and off-transient kinetics of pulmonary oxygen uptake in humans. J Physiol. 2001; 533:891-902.

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(15.) Rowntree D. Statistics Without Tears. London: Penguin, 1991.

(16.) Solberg G, Robstad B, Skjonsberg OH, Borchsenius F. Respiratory gas exchange indices for estimating the anaerobic threshold. J Sport Sci Med. 2005; 4:29-36.

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Disclaimer

The opinions expressed in JEPonline are those of the authors and are not attributable to JEPonline, the editorial staff or the ASEP organization.

Alessandro Moura Zagatto [1], Willian Eiji Miyagi [1], Raphael Luiz Sakugawa [1], Edson Itaru Kaminagakura [3], Marcelo Papoti [2]

[1] Laboratory of Research in Exercise Physiology (LAPEFE)/Federal University of Mato Grosso do Sul (UFMS), Campo Grande, Brazil, School of Physical Educationa and Sports of Ribeirao Preto, University of Sao Paulo (USP), Brazil, [3] LAFISE, Ponta Grosso State University, Ponta Grossa, Brazil.

Address for correspondence: Alessandro Moura Zagatto, Department of Physical Education, Federal University of Mato Grosso do Sul (UFMS), Av Costa e Silva s/n, Cidade Universitaria, CEP 79070-900 Campo Grande-MS, Brazil, Tel: + 55 67 3345 76 27, FAX + 55 67 3345 7630, E-mail: azagatto@yahoo.com.br
Table 1. Values of iRER = 1.00, [OBLA.sub.3.5], [AnT.sub.LAC] and RCP
and Metabolic and Respiratory Parameters Corresponding to these
Intensities.

                                               iRER = 1.00

Intensity (W)                                123.8 [+ or -] 5.6
Intensity at MAP (%)                          67.8 [+ or -] 1.9
V[O.sub.2] (ml x [kg.sup.-1][min.sup.-1])    29.7 [+ or -] 1.3
V[O.sub.2] at V[O.sub.2] max (%)             68.7 [+ or -] 1.6
HR (beats x [min.sup.-1])                   155.8 [+ or -] 2.8
HR at HR max (%)                             82.8 [+ or -] 1.0
RER                                                 --
[La] (mmol x [L.sup.-1])                     4.0 [+ or -] 0.2
RPE                                         11.6 [+ or -] 0.5

                                               [OBLA.sub.3.5]

Intensity (W)                                120.8 [+ or -] 6.5
Intensity at MAP (%)                           65.7 [+ or -] 2.2
V[O.sub.2] (ml x [kg.sup.-1][min.sup.-1])      30.5 [+ or -] 1.4
V[O.sub.2] at V[O.sub.2] max (%)               68.9 [+ or -] 2.1
HR (beats x [min.sup.-1])                     153.6 [+ or -] 3.2
HR at HR max (%)                              81.9 [+ or -] 1.4
RER                                          0.98 [+ or -] 0.01 *
[La] (mmol x [L.sup.-1])                             --
RPE                                          11.3 [+ or -] 0.6

                                              [AnT.sub.LAC]

Intensity (W)                                129.5 [+ or -] 5.3
Intensity at MAP (%)                         71.1 [+ or -] 1.8
V[O.sub.2] (ml x [kg.sup.-1][min.sup.-1])    31.5 [+ or -] 1.0
V[O.sub.2] at V[O.sub.2] max (%)             73.7 [+ or -] 1.8
HR (beats x [min.sup.-1])                   159.8 [+ or -] 2.8
HR at HR max (%)                             85.0 [+ or -] 1.2
RER                                         1.02 [+ or -] 0.01
[La] (mmol x [L.sup.-1])                     4.3 [+ or -] 0.3
RPE                                         12.0 [+ or -] 0.6

                                                    RCP

Intensity (W)                                126.8 [+ or -] 6.5
Intensity at MAP (%)                          69.2 [+ or -] 2.2
V[O.sub.2] (ml x [kg.sup.-1][min.sup.-1])    30.7 [+ or -] 1.4
V[O.sub.2] at V[O.sub.2] max (%)             71.2 [+ or -] 1.8
HR (beats x [min.sup.-1])                    157.6 [+ or -] 3.3
HR at HR max (%)                              83.7 [+ or -] 1.3
RER                                         0.99 [+ or -] 0.01 *
[La] (mmol x [L.sup.-1])                      4.2 [+ or -] 0.3
RPE                                          11.6 [+ or -] 0.5

                                            P-value

Intensity (W)                                0.09
Intensity at MAP (%)                         0.07
V[O.sub.2] (ml x [kg.sup.-1][min.sup.-1])    0.09
V[O.sub.2] at V[O.sub.2] max (%)             0.05
HR (beats x [min.sup.-1])                    0.33
HR at HR max (%)                             0.10
RER                                          0.02
[La] (mmol x [L.sup.-1])                     0.64
RPE                                          0.37

MAP = maximal aerobic power; V[O.sub.2] = oxygen uptake; HR = heart
rate; RER=respiratory exchange ratio; [La] = blood lactate response;
RPE = rate of perceived exertion. * P = 0.05 in relation to
[AnT.sub.LAC].

Table 2. Correlation Coefficients among the Physiological Parameters
and the Rate of Perceived Exertion Relatives to iRER = 1.00 with the
Same Parameters at [OBLA.sub.3.5], [AnT.sub.LAC] e RCP (* P = 0.05)

RER = 1.00                     [OBLA.sub.3.5]   [AnT.sub.LAC]    RCP

Intensity                          0.86 *          0.74 *       0.92 *
Intensity at MAP                   0.59 *           0.26        0.76 *
V[O.sub.2]                         0.79 *          0.68 *       0.90 *
V[O.sub.2] at V[O.sub.2] max       0.48 *           0.09        0.66 *
HR                                 0.66 *          0.62 *       0.86 *
HR at HR max                       0.51 *           0.33        0.75 *
Lactate                              --             0.33        0.69 *
RPE                                0.74 *          0.58 *       0.84 *
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Author:Zagatto, Alessandro Moura; Miyagi, Willian Eiji; Sakugawa, Raphael Luiz; Kaminagakura, Edson Itaru;
Publication:Journal of Exercise Physiology Online
Article Type:Report
Date:Oct 1, 2012
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