The lactate minimum test (LM) is considered a valid protocol for estimating the maximal lactate steady state (MLSS) intensity in only one test session (Bacon and Kern, 1999; Macintosh et al., 2002; Tegtbur et al., 1993; Simoes et al., 1999; Svedahl and Macintosh, 2003). The LM is comprised of an intense effort to hyperlactatemia induction, followed by a brief recovery period (i.e., ~ 8 min) and finally an incremental exercise phase. Therefore, during the hyperlactatemia induction phase, the LM allows the use of either an anaerobic test and consequently measurement of anaerobic power/capacity (Dantas De Luca et al., 2003; Zagatto et al., 2004; Pardono et al., 2008; Zagatto et al., 2014) or a graded exercise test (GXT) and the measurement of maximal oxygen uptake (V[O.sub.2MAX]) and maximal aerobic power (Johnson and Sharpe, 2011; Johnson et al., 2009). However, some studies report that one should be cautious in the choice of the hyperlactatemia induction mode (Johnson et al., 2009; Zagatto et al., 2014),as it can influence determination of lactate minimum intensity and physiological responses at lactate minimum intensity.
In addition, some studies have related the possibility of obtaining indices of maximal aerobic power (i.e., V[O.sub.2MAX] and the intensity associated with V[O.sub.2MAX]) during the incremental phase of the LM (Dantas De Luca et al., 2003; Simoes et al., 2003). In this way, the application of a procedure for assessing anaerobic fitness using hyperlactatemia induction would be possible, as well as the determination of V[O.sub.2MAX] and the lowest intensity where the V[O.sub.2MAX] is reached (iV[O.sub.2MAX]) during the incremental phase of the LM. This possibility makes the LM even more attractive for application in the training routines of athletes, because it would enable determination of anaerobic fitness during the induction phase and aerobic endurance, V[O.sub.2MAX] and iV[O.sub.2MAX], during the incremental exercise phase.
However, none of these studies (Dantas De Luca et al., 2003; Simoes et al., 2003) performed analysis to confirm whether the individuals actually reached V[O.sub.2MAX] during the GTX, such as attaining the oxygen uptake plateau (V[O.sub.2]), maximum heart rate achieved (HR), respiratory exchange ratio (RER) or peak lactate values (Mier et al., 2012; Midgley and Carroll, 2009; Howley et al., 1995). In addition, it has been recommended that progressive protocols for measuring the V[O.sub.2MAX] should have a length of around 10-12 minutes. This recommendation is due to evidence of a possible underestimation of V[O.sub.2MAX] values when using protocols of shorter or longer duration (Buchfuhrer et al., 1983; Yoon et al., 2007). Thus, the possibility of measuring the V[O.sub.2MAX] in the incremental phase of the LM is still not well established and needs further comparisons.
Therefore, the aim of this study was to investigate V[O.sub.2MAX] determination using the incremental phase of the LM on a cycle ergometer. Considering the findings of the studies that verified the possibility that V[O.sub.2MAX] can be obtained in a progressive test even after induction of lactic acidosis (Simoes et al., 2003; Dantas De Luca et al., 2003), we compared the highest V[O.sub.2] value measured in the incremental phase of LM with the V[O.sub.2MAX] determined during the GXT. As a hypothesis, we expected similar V[O.sub.2] values from both tests as reported in the literature.
Fifteen healthy trained men (twelve cyclists and three triathletes, aged 31 [+ or -] 6 years, height of 1.74 [+ or -] 0.07 m, body weight of 74.5 [+ or -] 9.9 kg, body mass index of 24.4 [+ or -] 2.6 kg x [m.sup.-2]), with a weekly training volume of between 200 and 400 km, voluntarily participated in the study. The sample size was calculated based on the similarity between values of peak oxygen consumption (V[O.sub.2-PEAK]) obtained in the incremental test performed with and without an effort to induce hyperlactatemia, as well as their correlation of 0.80 and 95% of test power, which resulted in a minimum sample size of ten participants. The sample size was calculated using G*Power 3.0.10 software, (G*Power, Franz Faul, Germany). All participants were informed about the possible risks and benefits of the study procedures and were only eligible for participation in the study after signing a written consent form. All procedures were approved by the Ethics Committee in Research of the Federal University of Mato Grosso do Sul (UFMS) (Process no. 1979/201) and were conducted according to the Declaration of Helsinki.
The subjects were instructed to avoid caffeine and alcohol during the evaluation period and not to perform strenuous exercise for at least 24 hours prior to each session.
All procedures were performed on an electromagnetic cycle ergometer (Ergoline ER 900, JAEGER, Germany), except for the Wingate test, which was conducted on a mechanically braked cycle ergometer (Biotec, CEFISE, Brazil). Participants performed two visits to the laboratory and were submitted to the graded exercise test (GXT) and lactate minimum test (LM), respectively. Prior to the two tests, a warm up lasting five minutes was performed at 75W, where the subjects were instructed to choose a cadence of their choice (75-90 rpm), which was standardized for both tests. These procedures were applied with a minimum interval of 48 hours.
During the GXT and the LM, the oxygen uptake (V[O.sub.2]), carbon dioxide production (VC[O.sub.2]), pulmonary ventilation (VE) and respiratory exchange ratio (RER) were measured breath-to-breath through a stationary gas analyzer (Quark PFT, COSMED, Rome, Italy). The gas analyzer was calibrated using known sample gases (3.98% C[O.sub.2] and 16.02% [O.sub.2]) and a pneumotachograph through a 3-liter syringe (Hans Rudolf, Kansas City, Missouri, USA), as recommended by the manufacturer. For the analysis of respiratory variables, data were smoothed each 5 points and interpolated each 1 second for the elimination of outlying data, as suggested by Ozyener et al. (2001). The heart rate (HR) was measured using a transmitter belt coupled to the gas analyzer. The Borg scale (620) was used to assess the rating of perceived exertion (RPE) which was measured at the end of each exercise stage of the incremental phase of the LM and GXT. In order to determine the starting values of V[O.sub.2], VC[O.sub.2], VE, HR and RER before the two tests (V[O.sub.2-START], VC[O.sub.2-START], [V.sub.E-START], [HR.sub.START] and [RER.sub.START], respectively), the average of 20 seconds immediately prior to the onset testing was determined. In the same way, the values at exhaustion for V[O.sub.2], VC[O.sub.2], VE, HR and RER (V[O.sub.2].PEAK, VC[O.sub.2-PEAK], [V.sub.E-PEAK], [HR.sub.PEAK] and [RER.sub.PEAK]) were considered as the highest average of the last 20 seconds of each incremental exercise stage (Poole et al., 2008).
For determination of blood lactate concentrations during the LM, blood samples from the earlobe were collected immediately after each stage of the incremental phase using a heparinized capillary and transferred to Eppendorf tubes containing 50 [micro]l of 1% sodium fluoride (NaF) for further analysis in an electrochemical lactate analyzer YSI 1500 Sport (Yellow Springs Instruments, USA). Blood samples were collected immediately prior to the GXT and LM for determination of lactate concentrations ([LAC.sub.START]), and also at 5 and 7 minutes after the GXT and LM to determine the peak lactate concentration ([LAC.sub.PEAK]).
Graded Exercise Test (GXT)
The GXT was performed five minutes after the warm up, with an initial intensity of 75W and 25W increments each minute until volitional exhaustion or until the subject could not maintain the pre-stipulated cadence.
The first ventilatory threshold ([VT.sub.1]) corresponded to the...