The highest velocity and the shortest duration permitting attainment of VO₂ max during running

A maior velocidade e o menor tempo de exercício em que o VO₂max é alcançado na corrida

Abstract

The severe-intensity domain has important applications for the prescription of running training and the elaboration of experimental designs. The objectives of this study were: 1) to investigate the validity of a previously proposed model to estimate the shortest exercise duration (T_LOW) and the highest velocity (V_HIGH) at which VO₂ max is reached during running, and 2) to evaluate the effects of aerobic training status on these variables. Eight runners and eight physically active subjects performed several treadmill running exercise tests to exhaustion in order to mathematically estimate and to experimentally determine T_LOW and V_HIGH. The relationship between the time to achieve VO₂ max and time to exhaustion (Tlim) was used to estimate T_LOW. V_HIGH was estimated using the critical velocity model. V_HIGH was assumed to be the highest velocity at which VO₂ was equal to or higher than the average VO₂ max minus one standard deviation. T_LOW was defined as Tlim associated with V_HIGH. Runners presented better aerobic fitness and higher V_HIGH (22.2 ± 1.9 km.h^-1) than active subjects (20.0 ± 2.1 km.h^-1). However, T_LOW did not differ between groups (runners: 101 ± 39 s; active subjects: 100 ± 35 s). T_LOW and V_HIGH were not well estimated by the model proposed, with high coefficients of variation (> 6%) and a low correlation coefficient (r<0.70), a fact reducing the validity of the model. It was concluded that aerobic training status positively affected only V_HIGH. Furthermore, the model proposed presented low validity to estimate the upper boundary of the severe-intensity domain (i.e., V_HIGH), irrespective of the subjects' training status.

Keywords:
Oxygen uptak; Physical education and training; Physical fitness; Running

Resumo

O domínio severo tem importantes aplicações para a prescrição do treinamento de corrida e elaboração de delineamentos experimentais. O estudo teve como objetivos: 1) investigar a validade de um modelo proposto previamente para estimativa do menor tempo de exercício (T_INF) e maior velocidade (V_SUP) em que o VO₂max é alcançado na corrida; e 2) comparar os efeitos do estado de treinamento nestes parâmetros. Oito corredores e oito indivíduos fisicamente ativos realizaram uma série de testes até a exaustão em esteira rolante para estimar matematicamente e determinar experimentalmente o T_INF e V_SUP. A relação entre tempo para atingir o VO₂ max e tempo de exaustão (Tlim) foi usado para estimar o T_INF. A V_SUP foi estimada pelo modelo de Velocidade Crítica. V_SUP foi assumida como a maior velocidade em que o VO₂ ± 2,1 km.h^-1. Entretanto, T_INF não foi diferente entre grupos (Corredores 101 ± 39; Ativos: 100 ± 35 s). V_SUP e T_INF não foram bem estimados pelo modelo proposto e apresentaram altos coeficientes de variação (> 6%) e baixa correlação (r < 0,70), o que diminuiu a sua validade. Pode-se concluir que o estado de treinamento aeróbio afetou positivamente apenas a V_SUP. Além disso, o modelo proposto apresentou baixa validade para predição do limite superior do domínio severo (V_SUP) independentemente do estado de treinamento dos indivíduos.

Palavras-chave:
Aptidão física; Corrida; Educação física e treinamento; Exercício

INTRODUCTION

Exercise intensities are classified into four domains based on the oxygen uptake (VO₂) response: moderate, heavy, severe, and extreme1^,2. The moderate domain comprises all exercise intensities that can be performed without a change in blood lactate in relation to resting values, i.e., below the lactate threshold. The heavy domain comprises all intensities between the lactate threshold and critical power, which corresponds to the highest constant intensity at which maximum oxygen uptake (VO₂max) is not reached3. Intensities just above critical power (i.e., 5 to 10%) permit VO₂max to be reached4^,5, thereby entering the severe domain which is characterized by all exercise intensities at which VO₂max is achieved. Finally, the extreme domain comprises even higher intensities when the individual reaches the point of exhaustion even before achieving VO₂max1^,2^,6.

Since the severe domain is the only intensity domain in which VO₂max is achieved during constant-load exercise, it represents an important physiological range for the prescription of high-intensity interval training7, which is necessary to provoke additional adaptations in aerobic parameters of trained athletes8. Furthermore, an inverse relationship between exercise intensity and the time to achieve VO₂max (TAVO₂max) exists in this domain. In other words, the higher the exercise intensity, the lower TAVO₂max1^,9^-11. If the exercise intensity continues to be high, at a certain point, the constant intensity exercise will be so high that the individual reaches exhaustion even before VO₂max is achieved12.

On the basis of this relationship, Hill et al.1, using cycle ergometer exercise, proposed a mathematical model that would supposedly estimate the highest intensity at which VO₂max is achieved (I_HIGH). This model estimates a single time point at which the time to exhaustion (Tlim) corresponds to the exact time when VO₂max is achieved (i.e., Tlim = TA-VO₂max). This time point corresponds to the shortest time necessary to achieve VO₂max during constant exercise (i.e., shortest exercise duration to achieve VO₂max, T). Finally, the intensity corresponding to T_LOW (i.e., I_HIGH) is estimated by the hyperbolic model of critical power3. Caputo and Denadai12subsequently demonstrated that I_HIGH is sensitive to aerobic training status. The authors observed that cyclists exhibited higher I_HIGH values in absolute terms (451 ± 33 vs. 269 ± 73 W) and relative to maximum aerobic power (130 ± 10 vs. 117 ± 6%), as well as lower T_LOW (117 ± 29 vs. 209 ± 29 s), when compared to untrained subjects. However, regardless of the training status of the subjects, the mathematical model proposed by Hill et al.1was not valid to predict T_LOW in the two groups. Furthermore, the validity of I_HIGH estimated with the model decreased with increasing aerobic training status of the subjects.

As a consequence, the mathematical model proposed by Hill et al.1showed poor validity in estimating the upper boundary of the severe-intensity domain during cycling12. The authors attributed this result to factors such as occurrence of the slow component of VO₂. Additionally, in the case of some subjects, the exercise intensities were so high and the exercise duration so short that TAVO₂max estimated by VO₂ kinetics (tau x 4.6) was higher than Tlim12. On the other hand, some studies have shown a lower magnitude of the slow component of VO₂ in running exercise compared to cycling13^-15. Moreover, in severe-domain exercise TAVO₂max seems to be lower in running than in cycling16. Therefore, application of this mathematical model to running in subjects with different training levels may improve the validity of the model, since the factors that affected the validity of the model in cycling (i.e., slow component of VO₂ and TAVO₂max) would be minimized. Additionally, since runners and active subjects differ in terms of TAVO₂max and VO₂ slow component amplitudes2, the use of these two groups may demonstrate the importance of these factors for the capacity of the proposed model to predict V_HIGH. Also, the higher intensity and shorter exercise duration at which VO₂max is reached and the corresponding effects of training status on these variables have not been studied in running. This evaluation can be useful for runners who aim to improve VO₂max, since the highest velocity at which VO₂max is achieved (V_HIGH) would correspond to the VO₂max reached within the shortest duration of constant-load exercise. This would represent a good physiological index for training prescription designed to increase maintenance times spent close to or at VO₂max. Finally, although the determination of V_HIGH requires a large number of tests, consequently impairing its use during training, the value that this intensity represents of the main aerobic parameters (e.g., vVO₂max, critical velocity) can be easily used for training prescription in subjects with different levels of aerobic fitness.

Therefore, the objectives of the present study were: 1) to investigate the validity of the linear regression model of the relationship between time to exhaustion and TAVO₂max in estimating T_LOW during running, and 2) to compare V_HIGH and T_LOW during running between runners and active subjects. On the basis of the lower magnitude of the VO₂ slow component and faster response of TAVO₂max during running, the model proposed by Hill et al.1could be valid to predict T_LOW in running. Furthermore, in view of the shorter response times of VO₂ to aerobic training2, a lower T_LOW and higher V_HIGH are expected in runners when compared to active subjects.

METHODS

Participants

Sixteen men volunteered to participate in the study and were divided into two groups: eight runners (27 ± 6 years, 67 ± 9 kg, 175 ± 8 cm) and eight active subjects (20 ± 2 years, 71 ± 3 kg, 175 ± 5 cm). The runners were 5- and 10-km specialists with a minimum experience of 2 years. The group of active subjects consisted of physical education students performing physical activity (soccer, indoor soccer, swimming, weight training) for at least 6 months, two times per week. Subjects undergoing systematic training for competitive purposes were excluded from this group. All participants were apparently healthy, non-smokers, and had no injuries. The volunteers were informed about the methodology of the study and signed a free informed consent form. The study was approved by the Ethics Committed of the State University of Santa Catarina (Universidade do Estado de Santa Catarina - Protocol No. 100/2010).

Experimental design

All subjects came to the laboratory in six to eight visits divided into three phases (Figure 1). In the first phase, body weight and height were measured, followed by an incremental test. In the second phase, three running tests until exhaustion were performed at 95%, 100% and 110% of vVO₂max for the determination of TAVO₂max and critical velocity (CV). The latter corresponds to the y-axis intercept of the line derived from the linear regression of velocity on the inverse of time to exhaustion. In the third phase, 2 to 4 running tests until exhaustion were performed to determine V_HIGH and T_LOW. In all tests of the second and third phase, the test was preceded by warming up for 10 min at 50% of the velocity corresponding to the lactate threshold, followed by 5 min of rest in the sitting position prior to the test. The tests were performed on a motorized treadmill (INBRAMED Millenium Super Atl, Inbrasport, Porto Alegre, Brazil) maintained at 1% inclination.

Figure 1
Schematic representation of the experimental protocol. The curves of oxygen uptake are merely illustrative. VO₂max, maximal oxygen uptake (dotted line); V_HIGH, highest constant velocity at which VO₂max is reached (solid line). For further details, see the Methods section.

The subjects were asked not to train exhaustively on the day prior to evaluation and to arrive at the laboratory in a fully fed and hydrated state. All procedures were carried out at the same time of day (±2 h), with an interval of 1 to 3 days between tests.

Incremental test

The initial load of the incremental test was 8 km.h^-1 for active subjects and 12 km.h^-1 for runners, with increments of 1 km.h^-1 every 3 min until voluntary exhaustion. At the end of each stage, the subjects interrupted the run for 30 seconds by holding onto the side bars of the treadmill and positioning their feet on the lateral borders to collect a 25-µl blood sample from the ear lobe for the determination of blood lactate concentrations. VO₂ was measured breath-by-breath throughout the test using a gas analyzer (Quark PFTergo, Cosmed, Rome, Italy), previously calibrated according to manufacturer instructions. The data were reduced to means of 15 seconds and the highest value was defined as the VO₂max of the incremental test (VO₂INC), which was used to determine the subject's VO₂max. The lowest velocity at which VO₂max was achieved was defined as vVO₂max. The intensity prior to the increase of 1 mmol.L^-1 in blood lactate concentrations in relation to resting values was considered the velocity at lactate threshold17. Blood lactate concentrations were determined in heparinized capillary blood analyzed immediately in an electrochemical analyzer (YSI 1500 Sport, Yellow Springs, OH, USA).

Determination of critical velocity

The subjects performed three time-to-exhaustion tests at 95%, 100% or 110%vVO₂max on three different days. These intensities were selected to induce a time to exhaustion between 2 and 15 min3. The tests were performed in a random order, with only one test per day. In all tests, the subject was encouraged verbally to maintain effort until voluntary exhaustion. VO₂ data were obtained in each test and reduced to means of 15 seconds. The highest VO₂of each test was determined and considered for the calculation of the subject's VO₂max (i.e., VO₂95%, VO₂100% and VO₂110%). For each intensity, Tlim was defined as the total exercise time. For the estimation of CV and D', the individual values of velocity and Tlim obtained were adjusted using a linear model of velocity versus the inverse of time (1/ time) as follows18:

where V is the constant exercise velocity (km.h^-1); Tlim is the time to exhaustion at the respective velocity (s); D' is the anaerobic distance capacity (m), and CV is the critical velocity (km.h^-1). Two parameters were derived from the equation: CV, which corresponds to the y-axis intercept of the line, and D', which corresponds to the slope of the line in relation to the x-axis.

Predicted V_HIGH and T_LOW

Linear regression was used to individually describe the relationship between TAVO₂max and Tlim. With TAVO₂max expressed as a function of Tlim, it was possible to identify the single Tlim at which VO₂max could hypothetically be achieved at the time of exhaustion (predicted T_LOW), i.e., when TAVO₂max = Tlim. V_HIGH was estimated withEquation 1, replacing Tlim with predicted T_LOW (Figure 2).

Figure 2
Relationship between time to achieve VO₂max (TAVO₂max) and time to exhaustion (Tlim) of tests performed at 95%, 100% and 110% vVO₂max in active subjects and runners. The estimate of the shortest duration when VO₂max is achieved (T_LOW) corresponds to the time when Tlim = TAVO₂max, i.e., the point of intersection of the trend line of regression between TAVO₂max and Tlim and the identity line (dashed line).

Determination of V_HIGH and T_LOW

Predicted V_HIGH was selected as the velocity of the first test for the determination of true V_HIGH. For this purpose, the subjects performed two to four constant velocity tests until exhaustion to determine V_HIGH. When VO₂max was achieved during the first test, the following tests were performed at a velocity that was 5% higher until VO₂max had not been achieved (as shown inFigure 1). Otherwise, if VO₂max was not reached during the first test, the following tests were performed at a 5% lower velocity12until VO₂max had been reached. VO₂ was measured throughout the protocol. As a criterion to achieve VO₂max, breath-by-breath data obtained in the V_HIGH test were analyzed as averages of 5 seconds. The mean of the three highest consecutive values (i.e., 15 s) of VO₂ in the V_HIGH test were defined as VO₂max of the V_HIGH test. This value had to be equal to or higher than VO₂max (mean of VO₂INC, VO₂95%, VO₂100% and VO₂110%) minus 1 intrasubject standard deviation (i.e., VO₂max - 1 SD) to considered the attainment of VO₂max12. V_HIGH was considered the highest constant velocity at which VO₂max was achieved. T_LOW was defined as Tlim associated with V_HIGH.

VO₂ kinetics

For each exercise transition, breath-by breath VO₂ responses were fitted using the following equation:

where VO₂(t) is the oxygen uptake at time t; VO₂b is the pre-exercise oxygen uptake; A is the asymptote of the amplitude, and τ is the constant time of oxygen uptake kinetics (defined as the time necessary to reach 63% of A). Occasional errant breaths were removed if they deviated more than four standard deviations from the local mean of 30 seconds19. For the tests at 95%, 100% and 110% vVO₂max, TAVO₂max was calculated as 4.6 x τ.

Statistical analysis

The results are expressed as the mean ± standard deviation. Normality of the variables was verified by the Shapiro-Wilk test. Characterization variables were compared between groups by the Student t-test for independent samples. Two-way ANOVA with repeated measures for one factor (i.e., intensity for the analysis of TAVO₂max and Tlim, and method used for the analysis of V_HIGH and T_LOW) was used for all other analyses. When a significant F value was found, an appropriate Student t-test was used to detect possible differences between two variables. The validity of the proposed model was also analyzed using Pearson's correlation test and typical error expressed as the coefficient of variation20. Pearson's correlation test and multiple (stepwise) linear regression analysis, grouping all subjects in the same group, were used to analyze the relationship of V_HIGH and T_LOW with the variables studied. A level of significance of P ≤ 0.05 was adopted in all analyses.

RESULTS

Incremental test and critical velocity

VO₂max, vVO₂max, CV (absolute and relative) and D' differed significantly (P ≤ 0.03) between groups (Table 1). The mean coefficient of determination of the CV model was 0.981 ± 0.026 in the two groups.

Table 1
Characteristics of the group and criticai velocity model.

	Active subjects	Runners
VO2max (ml.min.kg-1)	56.2 ± 3.3	62.0 ± 5.2*
vVO2max (km.h-1)	14.7 ± 0.9	18.3 ± 0.9*
CV (km.h-1)	12.2 ± 1.2	16.2 ± 1.1*
CV (%vVO2max)	83 ± 5	89 ± 2*
D' (m)	301 ±108	193 ± 57*

• CV: critical velocity; D': anaerobic distance capacity.
• ^*
  Significant difference between groups (P ≤ 0.03).

Responses in the constant-load tests

Analysis of variance of Tlim detected a significant F value in the factor intensity (P < 0.001) and in the interaction between the two factors (P = 0.017). Finally, pairwise comparison revealed no significant difference in Tlim at 95% vVO₂max (active: 585 ± 108 s; runners: 609 ± 115 s; P = 0.43) or 100% vVO₂max (active: 444 ± 108 s; runners: 360 ± 107 s; P = 0.08) between groups. However, Tlim at 110% vVO₂max was significantly higher (P = 0.007) in active subjects compared to runners (261 ± 67 versus 183 ± 50 s).

Regarding the comparison of TAVO₂max, ANOVA only detected a significant F value in the group (P < 0.001) and intensity (P < 0.001) factor. Pairwise comparison revealed no significant difference in TAVO₂max at 95% vVO₂max (active: 169 ± 41 s; runners: 129 ± 26 s) or 100 %vVO₂max (active: 173 ± 34 s; runners: 121 ± 22 s) between groups (P > 0.2). However, TAVO₂max at 110% vVO₂max was significantly lower in runners (active: 144 ± 28 s; runners: 88 ± 13 s) when compared to 95% and 100% vVO₂max (P< 0.01).Figure 3illustrates the VO₂ kinetics of a representative subject of each group at each intensity.

Figure 3
VO₂ responses at 95%, 100% and 110% vVO₂max obtained for a representative subjects of the group of runners (open circles) and active subjects (closed triangles). The graph includes residuals corresponding to runners (closed circles) and active subjects (open triangles) after adjusting the monoexponential function used. The dashed and dotted lines indicate the VO₂max of the active subject and runner, respectively.

Validity of the proposed model

Table 2shows the predicted and observed (true) values of V_HIGH and T_LOW for the two groups, as well as the relative and absolute consistency of the model proposed. For absolute V_HIGH, ANOVA detected a significant F value in the group (P < 0.05) and prediction model (P < 0.05) factor. When V_HIGH was expressed as relative values, only the prediction model factor was significant (P = 0.047). Furthermore, the same analysis detected a significant F value in the group factor (P ≤ 0.01) and in the interaction between factors (P < 0.01) for T_LOW.

Table 2
Observed (true) and predicted values of highest velocity (V_HIGH) and shortest duration (T_LOW) at which VO_2max is achieved in active subjects and runners.

		Mean ± SD		Model validity
Variable	Group	True	Predicted	Pearson	CV (%)
VHIGH(km.h-1)	Active	20.0 ± 2.1*	20.9 ± 3.7	0.33	12.5
	Runners	22.2 ± 1.9#	25.0 ± 2.7	0.61	6.5
VHIGH(%vVO2max)	Active	136 ± 14	142 ± 25	0.33	12.6
	Runners	122 ± 13#	137 ± 17	0.69	6.6
TLOW (s)	Active	100 ± 35	131 ± 18	-0.25	26.8
	Runners	101 ± 39	83 ± 16	-0.08	33.6

• CV: coefficient of variation.
• ^*
  Significant difference between groups (P < 0.05).
• ^#
  Significant difference between true and predicted values (P < 0.05).

Pairwise comparison revealed significant differences between groups for V_HIGH expressed as absolute values (P = 0.046), but no significant difference for T_LOW (P = 0.97). Moreover, a significant difference between predicted and observed values of V_HIGH (relative and absolute) was only observed in runners (P < 0.01). Finally, comparison between predicted and observed T_LOW showed no significant difference in either group (P > 0.09).

Figure 2shows the relationship between TAVO₂max and Tlim in the tests at 95%, 100% and 110% vVO₂max for the two groups. The coefficient of determination of this relationship was low in runners (r² = 0.79 ± 0.26) and active subjects (r² = 0.68 ± 0.39). There was no significant correlation between the observed and predicted values of any of the parameters, despite the observation of a significant trend in the correlation for V_HIGH in runners (P = 0.06). The coefficient of variation to estimate V_HIGH was higher in active subjects (12.5%) than in runners (6.5%). The coefficient of variation for T_LOW was high in both groups (> 25%).

Relationship between variables

V_HIGH was significantly correlated only with vVO₂max (r = 0.49; P = 0.05).

The multiple linear regression model showed that the main variables predicting V_HIGH are, in order of importance, vVO₂max and D'. The multiple correlation coefficient adding each variable was 0.49-0.63 (P = 0.03) and the equation estimated from this correlation was V_HIGH = 0.9 x vVO₂max + 0.011 x D' + 3.528. T_LOW was not correlated with any of the variables studied.

DISCUSSION

To our knowledge, this is the first study determining the highest velocity and shortest exercise duration at which maximal oxygen uptake is achieved during running and the influence of training status on these variables. One of the main results of this study was that V_HIGH was sensitive to training status. However, in contrast to our initial hypothesis, T_LOW did not differ between groups. Furthermore, the capacity of the proposed model to estimate V_HIGH and T_LOW was poor.

Prediction model of V_HIGH and T_LOW

In the present study, V_HIGH corresponded to 136 ± 14% of vVO₂max in active subjects, the same relationship estimated by Hill et al.1with a mathematical model in active subjects during cycling (i.e., 136% of maximal aerobic power). However, this similarity must have occurred by chance considering the differences in the exercise mode used. In view of this difference, we applied the model proposed by Hill et al.1to estimate V_HIGHand T_LOW. This model is based on a strong linear relationship between TAVO2max and Tlim, which was not strong in the present study, with a mean coefficient of determination of 0.68 ± 0.39 and 0.79 ± 0.26 for active subjects and runners, respectively. As a consequence, the model was also inefficient in estimating V_HIGH, probably because the estimate of V_HIGH obtained with the CV model depends on T_LOW estimated by the relationship between TAVO₂max and Tlim.

Some limitations of the present study regarding the estimation of V_HIGH and T_LOW should be taken into consideration. First, the model proposed is based on a strong linear relationship between TAVO₂max and Tlim1. However, in each group, TAVO₂max was significantly lower only at the intensity of 110% vVO₂max compared to the other intensities (95% and 100% vVO₂max). It is important to note that the extent of TAVO₂max was probably affected by the use of only one transition at each intensity24. This fact impairs the comparison of small changes in VO₂ kinetics during running exercises across the severe-intensity domain, i.e., those that already exhibited rapid VO₂ kinetics25. Therefore, using only one transition, the relationship between TAVO₂max and Tlim was compromised in the two groups studied and was apparently not linear, reducing the efficacy of the model to mathematically estimate T_LOW. However, only one transition was conducted for all evaluations due to the high requirements of the tests, large number of laboratory visits and low availability of the group of runners. Finally, the small number of subjects may reduce the power of the statistical test used by causing type II errors. However, despite the small number of subjects, the present study detected failures arising from this model and these failures would probably persist even if a larger number of subjects were included.

Effects of training status

The results of VO₂max, vVO₂max and CV obtained for the runners studied were similar to those reported in the literature for moderately trained athletes21. Furthermore, the aerobic fitness of active subjects was lower than that of runners, with the observation of lower aerobic indices and higher TAVO₂max at all intensities tested. However, active subjects exhibited a higher D', i.e., the characteristic of withstanding intensities above CV for a longer period of time22. This fact was demonstrated by the higher Tlim at the intensity of 110% vVO₂max in active subjects compared to runners.

As observed for other aerobic indices evaluated in the present study, V_HIGH was higher in runners and was consequently found to be sensitive to training status. Additionally, this parameter was correlated with vVO₂max, indicating that V_HIGH is an important aerobic index. However, multiple regression analysis suggests that V_HIGH is influenced by both vVO₂max and D'. This suggestion is in accordance with the study of Billat et al.10in which only subjects possessing higher D' values achieved VO₂max at 140% vVO₂max. However, it should be noted that vVO₂max was the main variable in multiple regression analysis, a finding corroborated by studies in which this threshold responded positively to aerobic training6^,12.

In contrast to V_HIGH, T_LOWwas similar in the runners and active subjects studied here. This result disagrees with Caputo and Denadai12who found a lower T_LOW in trained athletes due to aerobic adaptations that were responsible for a rapid VO₂ kinetic response2. In fact, a lower TAVO₂max in athletes was also observed in the present study. This finding might be due to the fact that active subjects were able to withstand intensities above the CV (i.e., higher D') for a longer period of time, resulting in the same Tlim at different relative intensities in the two groups (i.e., active subjects at a higher relative intensity than athletes). As a consequence, it is likely that the two groups studied present a similar TAVO₂max for the same Tlim in supramaximal exercises, since an increase in relative intensity reduces TAVO₂max1^,9^-11. These factors may explain in part the lack of a difference in T_LOW between groups.

In addition to the lack of difference in T_LOW between groups (active subjects: 100 ± 35 s; runners: 101 ± 39 s), the T_LOW values obtained here are lower than those reported by Caputo and Denadai12for cycling exercise (active subjects: 209 ± 29 s; runners: 117 ± 29 s). VO₂ kinetic responses in the severe domain have been shown to be faster in running when compared to cycling15^,23. Furthermore, when the same relative intensities are compared, cyclists showed a higher Tlim during cycling than runners during running16, which could explain the apparent differences in T_LOW between studies. Finally, despite lower aerobic fitness compared to runners, the active subjects studied here exhibited good aerobic conditioning, as demonstrated by the fact that their VO₂max (56.2 ± 3.3 ml.min.kg^-1) was similar to that of long-distance runners during cycling (54.6 ± 5.5 ml.min. kg^-1) and higher than that of untrained subjects (42.9 ± 3.5 ml.min.kg^-1) in the study of Caputo and Denadai12. Taken together, these factors seem to contribute to an apparent lower T_LOW in running compared to cycling.

CONCLUSION

The present study showed that the highest velocity at which VO₂max is achieved responds positively to aerobic training. However, on the basis of the multiple regression model used, training strategies designed to improve D' may also be important for improvement of V_HIGH. Finally, researchers and coaches should not rely on the mathematical estimation of V_HIGH and T_LOW, since the model proposed appeared not to be valid in running.

Acknowledgements

To Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support (Grant No. 478459/2008-4).

REFERENCES

• Hill DW, Poole DC, Smith JC. The relationship between power and the time to achieve VO2max. Med Sci Sports Exerc 2002;34(4):709-14.
• Burnley M, Jones AM. Oxygen uptake kinetics as a determinant of sports performance. Eur J Sport Sci 2007;7(2):63-79.
• Vanhatalo A, Jones AM, Burnley M. Application of critical power in sport. Int J Sports Physiol Perform 2011;6(1):128-36.
• Poole DC, Ward SA, Gardner GW, Whipp BJ. Metabolic and respiratory profile of the upper limit for prolonged exercise in man. Ergonomics 1988;31(9):1265-79.
• De Lucas RD, De Souza KM, Costa VP, Grossl T, Guglielmo LGA. Time to exhaustion at and above critical power in trained cyclists: The relationship between heavy and severe intensity domains. Sci Sports 2013;28(1):9-14.
• Caritá RAC, Caputo F, Greco CC, Denadai BS. Aptidão aeróbia e amplitude dos domínios de intensidade de exercício no ciclismo. Rev Bras Med Esporte 2013;19(4):271-4.
• Duffield R, Edge J, Bishop D. Effects of high-intensity interval training on the VO2 response during severe exercise. J Sci Med Sport / Sports Medicine Australia 2006;9(3):249-55.
• Laursen PB, Jenkins DG. The scientific basis for high-intensity interval training: optimising training programmes and maximising performance in highly trained endurance athletes. Sports Med 2002;32(1):53-73.
• Margaria R, Mangili F, Cuttica F, Cerretelli P. The kinetics of the oxygen consumption at the onset of muscular exercise in man. Ergonomics 1965;8(1):49-54.
• Billat VL, Blondel N, Berthoin S. Determination of the velocity associated with the longest time to exhaustion at maximal oxygen uptake. Eur J Appl Physiol Occup Physiol 1999;80(2):159-61.
• Hill DW, Stevens EC. VO2 response profiles in severe intensity exercise. J Sports Med Physical Fitness 2005;45(3):239-47.
• Caputo F, Denadai BS. The highest intensity and the shortest duration permitting attainment of maximal oxygen uptake during cycling: effects of different methods and aerobic fitness level. Eur J Appl Physiol 2008;103(1):47-57.
• Jones AM, McConnell AM. Effect of exercise modality on oxygen uptake kinetics during heavy exercise. Eur J Appl Physiol Occup physiol 1999;80(3):213-9.
• Carter H, Jones AM, Barstow TJ, Burnley M, Williams CA, Doust JH. Oxygen uptake kinetics in treadmill running and cycle ergometry: a comparison. J Appl Physiol 2000;89(3):899-907.
• Caputo F, Denadai BS. Exercise mode affects the time to achieve VO2max without influencing maximal exercise time at the intensity associated with VO2max in triathletes. Int J Sports Med 2006;27(10):798-803.
• Caputo F, Mello MT, Denadai BS. Oxygen uptake kinetics and time to exhaustion in cycling and running: a comparison between trained and untrained subjects. Arch Physiol Biochem 2003;111(5):461-6.
• Coyle EF. Integration of the physiological factors determining endurance performance ability. Exerc Sport Sci Rev 1995;23:25-63.
• Whipp BJ, Huntsman DJ, Stoner N, Lamarra N, Wasserman K. A constant which determines the duration of tolerance to high-intensity work. Federation Proceedings. 1982;41(5):1591.
• 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; 15;533(Pt 3):891-902.
• Hopkins WG. Measures of reliability in sports medicine and science. Sports Med 2000;30(1):1-15.
• Kilding AE, Winter EM, Fysh M. Moderate-domain pulmonary oxygen uptake kinetics and endurance running performance. Journal of sports sciences 2006 Sep;24(9):1013-22.
• Chidnok W, Dimenna FJ, Bailey SJ, Wilkerson DP, Vanhatalo A, Jones AM. Effects of pacing strategy on work done above critical power during high-intensity exercise. Med Sci Sports Exerc 2013;45(7):1377-85.
• Hill DW, Halcomb JN, Stevens EC. Oxygen uptake kinetics during severe intensity running and cycling. Eur J Appl Physiol 2003;89(6):612-8.
• Lamarra N, Whipp BJ, Ward SA, Wasserman K. Effect of interbreath fluctuations on characterizing exercise gas exchange kinetics. J Appl Physiol 1987;62(5):2003-12.
• Buchheit M, Laursen PB, Ahmaidi S. Effect of prior exercise on pulmonary O2 uptake and estimated muscle capillary blood flow kinetics during moderate-intensity field running in men. J Appl Physiol 2009;107(2):460-70.

Publication Dates

• Publication in this collection
  Mar-Apr 2015

History

• Received
  18 Aug 2014
• Accepted
  10 Nov 2014