606 men completed a maximal incremental exercise test until exhaustion using a cycloergometer (Jaeger ER 800, Germany) or a treadmill (H/P/COSMOS 3PW 4.0, H/P/Cosmos Sports & Medical, Nussdorf-Traunstein, Germany): 251 cyclists, 104 triathletes, 53 swimmers, 51 track athletes, 17 basketball players, 26 football players, 12 gymnasts and 92 physical education (PE) students. All tests were performed under similar atmospheric conditions (temperature 22.8±0.6°C; relative humidity 62.5±4.4%; barometric pressure 703.54±7.41mmHg). All subjects were informed about the nature of the study and gave their signed consent for participation, in accordance with the norms set out by the Declaration of Helsinki regarding research involving human subjects.14 All mentioned procedures in the present research were approved by our Local Ethics Committee.

All participants performed a maximal incremental exercise test to determine their maximal oxygen uptake (VO2max) and VTs. Verbal encouragement was provided to ensure that maximal effort was reached. Gas exchange data was continuously collected during each test using an automated breath-by-breath system (Jaeger Oxycon Pro gas analyser, Erich Jaeger, Viasys Healthcare, Germany). The volume signal and gas analysers were calibrated with a syringe of known precision and volume of analyzed gas mixture, respectively. The values were averaged for a 60s period. A 12-lead electrocardiogram (ECG; Viasys Healthcare, Germany) was continuously recording during the tests to determine the Heart Rate (HR). At least two of the following criteria were required for the attainment of VO2max: the plateau in VO2 values despite increasing workload, RER≥1.1, or the attainment of 95% of the maximum theoretical heart rate (HRmax).7,15 The VTs were determined according to the criteria proposed by Davis (1985) and Siegler, Gaskill and Ruby (2003), whilst VO2max obtained were determined according to Lucia et al. (2006), and were set in a specific manner in order to achieve the point of maximal agreement between the different methods of assessment. The results from all the tests were evaluated by two researchers in a double blind process. The coefficient of variation between the assessments of these two researchers and those of a highly-experienced expert was 1.3%.

The calculation for ITA as well as the correction (CITA) was performed according to the elementary model proposed by Peinado et al. (2014): the area under the curve (the ITA) for the functions VO2/VE (L2min2), load÷VO2 (WLmin2) and Load/VE (WLmin2). It is calculated as the sum of the area of the triangle and the rectangle below the function VE/load (see Fig. 1).13

Figure 1.

Elemental procedure for calculating the ITA for the function VO2/VE.

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Data were tested for normality, based on skewness (−2<z<2) and kurtosis (−2<z<2) using the Kolmogorov–Smirnov test. The Pearson's bivariate correlation analysis was performed to examine the relationship between performance variables, VO2 and the ITA. Differences between the results of the two subject groups were compared using the Independent Samples Student t Test. Effect sizes between the different methods of expressing the VTs were calculated using Cohen's d; using the means and the pooled standard deviations of the measurements from the conditions. Cohen's d was corrected for dependence among means by using the correlation between the two means. Interpretation of Cohen's d: an effect size of less than 0.33 is considered small, while 0.33–0.55 is considered moderate and effect sizes of 0.56–1.2 are considered large. Comparisons were two-tailed. All data were prepared and analyzed using SPSS v15.0® (SPSS Worldwide Headquarters, Chicago, IL) software. The significance level for all studies was set at p<0.05.

Ideally, the VTs, which mark the boundaries of the aerobic–anaerobic transition, should be as close as possible to the VO2max; as such so that the body may experience conditions where oxygen can be used efficiently for as long as possible. During acidosis, which begins when VT1 is surpassed, compensatory hyperventilation facilitates the continuation of exercise as lactic acid builds up. Therefore, it is plausible to argue that a higher ITA is the result of a greater capacity to undertake endurance tests, and illustrates that the subject is able to compensate for the increase in the lactic acid. Thus, a strong correlation exists between lactate and VTs.3–5,16 Once the VT2 is surpassed, the plasma lactic acid concentration increases markedly. This is the result of increased lactic acid production and a decreased rate of clearance. As a result, our research demonstrates that the highest ITA values are found in cyclists and triathletes; sports where high endurance capacity is vital for high-level performance. However, one cannot simply explain the high value of ITA reported in basketball players, as basketball is not considered as endurance dominant.17

The highest ITA values were obtained for cycling, followed by triathlon and basketball. Athletics (track) and basketball reported the highest aerobic threshold values (%) in relation to VO2max, above all other sports (see Fig. 2). There is a significant difference between the results of the anaerobic threshold (%) and the peak oxygen consumption between sports.

Figure 2.

Inter-ventilatory threshold area average values of the different sports.

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Mean values for cyclists’ aerobic threshold, expressed in percentages, were 56.6±7.5%. Our results are similar to those reported by Zapico et al. (2007): November–December (50±2.4%), January–February (61±2.1%) and May–June (56±2%). However, they are well below the values by Pardo (2001): November–December (76.1±1.3%) January–February (72±1.5%) and May–June (73.1±1.3%); who analyzed the evolution of aerobic–anaerobic transition throughout a competitive season. Our results also differ from those found by Withers et al. (1981) (66.3%), and Simon et al. (1986) (65.8%). The differences may be due to variations in the terminology and methodology used to determine the aerobic–anaerobic transition.2 The relationships between the ITA for the function VO2/VE and the VT2 (associated with present ergospirometric variables) are explained by the fact that a higher VT2 results in a larger ITA. The positions of VT1 and VT2 in the cyclists, in the present investigation, are similar to those reported in other studies.9,11,18–20 Overall, the ITA of the cyclists was higher in comparison to the other sports with lower endurance characteristics.

In our research, the mean values for the triathletes’ aerobic and anaerobic thresholds, expressed in percentages, were 58.6±9.3% and 86.0±6.4%, respectively. Galy et al. (2003) investigated the evolution of the physiological parameters over seasonal parameters, and found an aerobic threshold rate ranging from 73.8±0.2% and 75.6±0.2%; and for the anaerobic threshold of 79±0.2% and 88.9±0.2. It is plausible to assume that the differences in reported aerobic threshold values, between the investigations, are a result of the method used to determine the aerobic–anaerobic transition. We discovered that the method used was the same as ours.21 Other studies22–25 reported large variations in VTs (ranging between 61% and 81%). Again, the differences and variability can be explained by nomenclature used in terms of aerobic–anaerobic transition,2 the methods for determining the thresholds21 and the mode of exercise.26

For swimming, soccer, gymnastics, athletics (track), and PE, the percentages of the aerobic threshold, with respect to VO2max, were very similar (ranged between 51.7% and 55.8%), but lower than endurance-specific sports. Therefore, the higher values obtained for this parameter in the aerobic–anaerobic transition are for athletics (track) (65.0±8.6%) and basketball (64.6±10.2%). The mean percentage of the anaerobic threshold is very similar for all sports (ranging from 80% to 89%). Our results are in accordance with those reported by Bunc et al. (1987) where a total of 223 highly trained track athletes were studied. In particular, the anaerobic threshold percentage values ranged between 80.5% and 86.6%.6 Track athletes and basketball players have the highest aerobic threshold percentage values with respect to the VO2max, above all other sports. Between sports, there is a significant difference in reported anaerobic threshold percentages from the peak oxygen consumption.

In this study, we assessed the degree of association between VTs in the two categories of track athletes studied. We believe that the manner one expresses the VTs can result in significantly different outputs. The calculation of the ITA aims to aid and explain the high values commonly found in endurance track athletes. One would expect that track athletes with a greater endurance component (in both training and competition) would report significantly high relative values. However, no significant differences between groups with a high and low endurance component were reported for both VT1 (59±8.3% versus 56.8±9.4%), and VT2 (85.5±6.5% versus 84.6±6.3%).

In this study, individuals with a low endurance capacity displayed an average VT1 value of 55.94±10.3 and VT2 value of 84.26±6.9, respectively; while individuals with a high endurance capacity had values of 57.88±8.5 and 85.4±6.4, respectively. When the effect size is calculated, the average athlete with a high endurance capacity would approximately exceed 58% (d=0.20; 57.8%) of the sample of athletes with a low endurance capacity. Therefore, it is not convenient to express VTs as a percentage of VO2max. However, the effect size for inter-ventilatory threshold area and VTs expressed in absolute values (ml/min) are appropriate ways to express the aerobic–anaerobic transition.

The effect size for absolute values of VT1 and VT2 of athletes with low endurance, 2253±606.26 for (VT1) and 3381.76±641.87 (VT2), means that approximately 71% could have higher values than the corresponding population of athletes with low endurance [2614.50±635.09 and 3856.91±787.02 for VT1 and VT2, respectively) (d=0.50, 69.1%)]. The effect size for the inter-ventilatory threshold area is less (d=0.40, 65.5%) than VT1 and VT2 in absolute values. We believe it is appropriate to express the VTs first as absolute values, and secondly as values in terms of inter-ventilatory threshold area, but never as percentages of VO2max.

When the obtained effect size is estimated over 58% (d=0.20; 57.8%) of the athlete population with a low endurance capacity, VT1 and VT2 values will differ from the average athlete sample with high endurance. Therefore, it is not convenient to express the VTs as percentages of VO2max. However, the effect size of the ITA and VTs expressed in absolute values (ml/min) are appropriate ways to express the aerobic–anaerobic transition. Approximately 66% of the population with low endurance would be higher than the corresponding area of high endurance (d=0.40; 65.5%); whilst almost 71% of the ventilatory threshold (ml/min) would be higher in endurance track athletes. Therefore, it seems appropriate to express the VTs first as absolute values, and secondly as values in terms of inter-ventilatory threshold area.