The main adaptation to endurance training is an increased oxidative capacity because of mitochondrial biogenesis and increased fatty acid use as fuel (13). Evaluating performance through the application of adequate physical tests during a sportive season may be a useful tool to indirectly evaluate these training adaptations and also for the prescription of training intensities (11).
Treadmill incremental V̇O2max tests with gas exchange analysis have been widely used during training programs for runners to evaluate program effects and to determine target intensities. However, these tests often differ in their methodological characteristics, such as stage duration, grade, and speed increment size (1,2,10,20,23). Even with the availability of treadmills with computational speed control, classical protocols using grade variations to adjust exercise intensity during tests are still commonly used and can hinder the practical application of laboratory information (20).
To be applicable for runners, a V̇O2max test protocol should approximate actual training and outdoor race conditions to unequivocally determine maximal (and also submaximal) parameters such as the ventilatory threshold (VT) and respiratory compensation point (RCP). Determining the speeds related to these parameters facilitates the definition of 3 exercise intensity domains for training prescription: moderate (below VT), heavy (between VT and RCP), and severe (above RCP) (2,20,25). Previous studies have shown that speeds related to VT (sVT) and V̇O2max (sV̇O2max) can be used to estimate an athlete's performance in endurance events (12,21).
Relatively short ramp protocols have been regarded as suitable for sV̇O2max, sVT, and the running speed related to RCP (sRCP) determinations via pulmonary gas exchange (2). However, stage protocols lasting >3 minutes result in a lower V̇O2max without consistency for sVT and sRCP determinations through gas analysis (2,4,30). It seems that smaller speed increments are more appropriate for determining sVT, sRCP, and sV̇o2max because of the mild adjustment of oxidative and glycolytic enzymes to compensate for the new adenosine triphosphate (ATP) demands (5,20).
The oxygen uptake (V̇o2) kinetic studies have shown that V̇O2 measured after ∼15 to 25 seconds of exercise (“fundamental exponential phase” or phase II) approximates the real muscular oxygen consumption. The duration of this phase is inversely related to exercise intensity because of the slower transit time of blood from muscles to lungs and the increase in muscle vasodilatation and the right shifting of the HbO2 dissociation curve. These events help to adjust mitochondrial respiration during exercise (9,18,26,28).
Another important point that must be noted in V̇O2max tests for runners is reproducibility. Test reproducibility refers to the consistency of repeated tests of an athlete's performance. Protocols with poor reproducibility are inappropriate for tracking changes in performance between trials or assessment of performance in a single trial. Indeed, in a recent meta-analysis (6,11), only 25% of 40 studies measuring reproducibility of incremental tests analyzed the reproducibility of the ventilatory threshold (VT), RCP, or V̇O2max parameters with gas analyzers. Moreover, all of these studies included only 2 protocol repetitions, which may result in significant overestimation or underestimation of the results (23,24).
Experimental Approach to the Problem
The aim of this study was to verify the reproducibility and determine the running speeds related to maximal and submaximal parameters of a specific incremental maximum effort treadmill protocol for amateur runners. Measurements of maximal and submaximal parameters, and also the running speed related to these parameters, were collected to improve specific training intensity prescriptions. To accomplish this aim, athletes made 6 visits to the laboratory, with at least 48-hour rest between visits, and participated in 2 familiarization sessions with the laboratory conditions and 4 repetitions of the proposed protocol.
Eleven male amateur runners (38.4 ± 4.8 years old, 66.1 ± 5.8 kg, and 1.67 ± 0.05 m tall) who specialized in 10-km runs participated in this study. All of the subjects had >1 year of running training with weekly programs of 3-5 runs varying from a total of 40-100 km·wk−1. The subjects were advised to maintain normal food intake and refrain from physical activity during the period of the experiments. All of them were informed of the procedures and gave their written consent to participate in the study according to the guidelines of the Research Ethics Committee of the University.
The subjects made 6 visits to the laboratory as indicated above. To avoid circadian variations, the individual tests were performed at the same time each day (3).
The subjects had 2 familiarization sessions with the treadmill, facemask, and laboratory conditions (temperature and environment) before starting the protocol. In the first visit, athletes ran for 30 minutes wearing a facemask. The treadmill speed was increased until a comfortable speed was reached above the walk-to-run transition (9 km·h−1). During the second visit, a test simulation with all equipment was done. After that, participants were subjected to 4 repetitions (T1, T2, T3, and T4) of the proposed protocol (below).
After 3 minutes of warm-up at 8-8.5 km·h−1, athletes started the protocol at 9 km·h−1 with a fixed treadmill grade of 1% (15). This initial running speed was determined as the running speed reached in the previous familiarization sessions. After each 25-second interval, the speed was increased by 0.3 km·h−1 until volunteers reached exhaustion. Athletes were encouraged to continue for as long as possible. After exhaustion, the athletes underwent a 5-minute recovery protocol during which the speed was decreased each minute from 100% to 60, 55, 50, 45, and 40% of the maximal achieved speed.
The V̇O2, carbon dioxide output (V̇co2), and respiratory exchange rate (RER) were measured breath-to-breath using a gas analyzer (CPX/D Med Graphics, St. Paul, MN, USA). The average values of each variable at every 25-second stage were used to analyze data and relate them to phase II of the V̇O2 kinetics. Before each test, the analyzer was calibrated with a known gas mixture (12% O2 and 5% CO2), and the volume sensor was calibrated with a 3-L syringe. Heart rate (HR) was measured continuously via a Polar® heart monitor interface (Polar Electro Oy, Helsinki, Finland).
The last completed stage was used to determine V̇O2max, maximal achieved speed (sV̇O2max), maximal V̇co2 (V̇co2max), maximal respiratory exchange ratio (RERmax), and maximal HR (HRmax). The V̇O2max achieved was assessed in the presence or absence of the V̇O2 “plateau” during the protocols (22).
Ventilatory Threshold and Respiratory Compensation Point Determinations
To determine VT and RCP, the V-Slope method was used (1). This method allows the characterization of VT and RCP through the loss of linearity from V̇co2/V̇O2 and from V̇E/V̇co2 plots, respectively. Afterward, the V̇O2 (V̇O2VT; V̇O2RCP), V̇co2 (V̇co2VT; V̇co2RCP), RER (RERVT; RERRCP), running speed (sVT; sRCP), and HRs (HRVT; HRRCP) related to these parameters were determined.
The possible presence of learning effects and of statistical differences between the means for each trial was tested using repeated-measures 2-way analysis of variance with Tukey's post hoc test when applicable. Significant differences were considered when p < 0.05.
The reliability of the protocol was analyzed using the within-subject variations to compute the typical error (TE), according to the recommendation of Hopkins (14). To allow comparison across trials, the coefficient of variation (CV%) was calculated by dividing TE by the variable's mean among the group in all repetitions. The lower and upper confidence limits (CL95%) of the TE were also reported to analyze the precision and sensibility of the protocol. The results for all athletes in each parameter are presented as the mean ± SD for each test, with CV%, TE, and CL95% characterizing the 4 tests.
A typical example of a ventilatory response of 1 athlete during the protocol is shown in Figure 1A. A linear fit of ventilatory parameters during the test allowed an accurate estimation of VT (Figure 1B) and RCP (Figure 1C) by the V-Slope method. A reasonable and similar number of stages were found in each intensity domain, moderate (10.7 ± 0.5 stages), heavy (9.4 ± 0.4 stages), and severe (12.9 ± 0.4 stages), contributed to the determination of these parameters.
The effects of the protocol on VT parameters during all repetitions are shown in Table 1 (mean ± SD, n = 11). The mean CV%, TE, and its CL95% are also shown.
No significant differences were found in any parameter analyzed across T1, T2, T3, and T4 (p > 0.05). The mean CV% values indicated TEs ranging from 4% (RERVT) to 7% (V̇co2VT). Note that for sVT (the most important parameter for training prescription), the mean CV% was 5%, indicating good test reproducibility. Furthermore, the TE found for sVT (TE = 0.62 km·h−1) represents 2 stages in the protocol, which indicate high sensitivity.
The same data for RCP during all trials are shown in Table 2. We found no significant differences in RCP parameters across T1, T2, T3, and T4 (p > 0.05). The mean CV% values for V̇O2RCP and sRCP were lower than 2.5%. The TE of sRCP (0.35 km·h−1) was lower than observed in sVT, and represents only one stage in the protocol.
The measurements of V̇O2max parameters are shown in Table 3 (mean ± SD, n = 11). Again, no differences were found across T1, T2, T3, and T4 for V̇O2max parameters (p > 0.05). Some of them showed CV% = 9.1% (V̇O2max) or 8.5% (V̇co2max), but we found CV% = 2.5% for sV̇O2max, indicating high reproducibility of the protocol for speed determination. The TE of sV̇O2max (0.43 km·h−1) was similar to the TE values of sVT and sRCP.
We propose here a specific maximum effort protocol for runners based on metabolic premises regarding the kinetics of V̇O2 and treadmill inclination which simulates training conditions as closely as possible. Our objective is to apply the test results to indicate training intensity prescriptions and to analyze endurance training effects.
The reproducibility of the protocol is demonstrated through the expressed TE or in percentile terms (CV%) to facilitate comparison with other studies. According to Brisswalter (3), it is desirable that the intraindividual day-to-day CV% remains between 4 and 7%.
The values of CV% for V̇O2max were higher than those reported by Rivera-Brown (24) (CV% = 2%; n = 19) and Weltman et al. (29) (CV% = 4.8%, n = 15). The inherent biological variability associated with breathing variables and the different levels of athletes' physical conditioning in each study can explain the differences of CV% at V̇O2max. However, it is important to point out here that the mean value of CV% for sV̇o2max was lower than that shown by Billat et al. (2.3 vs. 5%, respectively). The variation in measured V̇O2max was always greater than the variability in the peak speed attained during our protocol, a parameter of practical use. It is possible that the smaller increments and shorter stage duration used in our protocol contribute to more precise sV̇O2max determinations.
The CV% at V̇o2VT (CV% = 6%) was closer to that obtained by Meyer et al. (19) and Caiozzo et al. (4) (CV% = 5.6 and 6.3%, respectively). These authors analyzed the athletes on a bicycle and had fewer volunteers (n = 7) and repetitions (n = 2) than this study. Davis et al. (7), analyzing 30 students in 2 repetitions on a treadmill, also found mean values of CV% (6.3%) closer to those found here. Further, the CV% for sVT (CV% = 5.2%) was similar to that shown by Dickhuth et al. (CV% = 5.8%) who analyzed 11 healthy volunteers (8). We also found low CV% for sRCP (2.4%) and V̇O2RCP, but the comparison of these results with literature data is difficult because of shortage of studies analyzing variables at RCP.
The TE results presented here for training intensity parameters such as sVT (TE = 0.62 km·h−1), sRCP (TE = 0.35 km·h−1) and sV̇O2max (TE = 0.43 km·h−1) indicate high sensitivity and reproducibility of this protocol.
The relationship between stage duration and speed increment facilitated the determination of VT and RCP (Figures 1B, C) by generating a similar number of stages at each intensity domain: moderate, heavy, and severe. However, the average number of stages produced a total test time (13.8 ± 1.3 minutes) close to that used in other studies (20).
The stage duration used here was likely sufficient to reach phase II and mitochondrial adjustment in energy generation at each stage (27,28). The use of the 0.3 km·h−1 speed increment contributed to lower variation in muscular metabolism, facilitating mitochondrial adjustment and consequently the quantification of real V̇O2 in each stage (16,28). Also, the use of a 1% fixed treadmill inclination grade allows the practical application of the results obtained in the laboratory, besides minimizing the V̇O2 decrease during increases in the treadmill grade (1,2,10,17,20,23). Furthermore, the warm-up phase used here (3 minutes to 8-8.5 km·h−1) is closer to the initial test speed (9 km·h−1) and seems to have allowed a stabilization of ventilatory parameters before the incremental phase, thereby reducing transient effects.
The upper CL (CL95%) of the TE determinations can be used by coaches and researchers in their routines by enabling them to determine whether real changes have occurred after a training program. For example, if the test and retest difference for an athlete exceeds a ±0.44 km·h−1 range for sRCP, the change is likely to be significant (p < 0.05). On the other hand, a difference within that range may be because of noise in the protocol or to biological variations. It should also be noted that this concept may have implications for the measurement of small performance variations in other parameters besides VT, RCP, and V̇O2max as well.
We thank the athletes who participated in this research. This study was supported by the scientific agencies, São Paulo Research Foundation, and CNPq (03/09923-2P and 523383-96-7). Thiago Fernando Lourenço received grant (07/53135-0) from the Fapesp.
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