Accuracy of VO2max and anaerobic threshold determination

Abstracts

Studies on the accuracy of the gas exchange and ventilation parameters during exertion involving the Brazilian population are scarce in literature. OBEJCTIVE: To determine the reliability of the maximal oxygen intake (VO2max) and anaerobic threshold (AnT), as well as the objectivity of the AnT determination in Brazilian healthy youth adults. METHODS: Two tests of maximal exertion were applied. Two independent observers applied the visual inspection method for the AnT determination. The data were compared by means of the regression analysis, intraclass correlation coefficient (ICC), two-way ANOVA and the paired t-test for an alpha < 0.05. The intra-observer and intra-subject variabilities were determined by means of the typical error (s) and variation coefficient (VC). RESULTS: No significant differences between tests for the VO2max and AnT determination as well as between observers in AnT determination were observed. The new VO2max presented ICC = 0.97, s = ± 0.14 L • min-1, and VC = ± 5.5%. The AnT presented ICC = 0.90, s = ± 0.14 L • min-1, and VC = ± 9.2%. The inter-observers AnT determination presented ICC = 0.95, s = 0.1 L • min-1 and VC = 5.6%. CONCLUSION: The VO2max and the AnT are reliable measurements, and the AnT determination was demonstrated to be an objective method in the population studied.

Reliability; Objectivity; Maximal oxygen intake; Anaerobic threshold and ventilatory threshold

São raros estudos que tratam da acurácia de parâmetros de trocas gasosas durante o esforço, com a população brasileira. OBJETIVO: Determinar a confiabilidade do consumo máximo de oxigênio (VO2max) e do limiar anaeróbio (LAn), assim como, a objetividade do segundo (LAn) em adultos jovens saudáveis. MÉTODOS: Foram aplicados dois testes de esforço máximo, a partir dos quais dois observadores independentes determinaram o LAn através do método de inspeção visual. Os dados foram tratados por meio da análise de regressão, coeficiente de correlação intraclasse (CCI), ANOVA com dois fatores com teste post hoc de Tukey e teste t pareado para alfa < 0,05. As variações intra-observadores e intra-sujeitos foram determinadas por meio do erro típico (s) e coeficiente de variação (CV). RESULTADOS: Não houve diferença significativa entre os testes para o VO2max e LAn. Não foram observadas diferenças significativas entre testadores para a determinação do LAn. O VO2max apresentou entre os dois testes CCI = 0,97, s = ± 0,14L • min-1 e CV = ± 5,5% e para o LAn o CCI = 0,90, s = ± 0,14L • min¹, e CV = ± 9,2%. A determinação do LAn interobservadores apresentou CCI = 0,95, s = ± 0,10L • min-1 e CV = ± 5,6%. CONCLUSÃO: O VO2max e o LAn foram medidas satisfatoriamente precisas.

Objetividade; Consumo máximo de oxigênio; Limiar de lactato e limiar ventilatório

Son raros los estudios que tratan de la exactitud de los parámetros de cambios gaseosos durante el esfuerzo con la población brasileña. OBJETIVO: Determinar la confiabilidad del consumo máximo de oxigeno (VO2max) y del umbral anaeróbico (LAn), así como la objetividad del segundo, (LAn) en adultos jovenes saludables. MÉTODOS: Fueron aplicados dos tests de esfuerzo máximo, a partir de los cuales dos observadores independientes determinaron el LAn a través del método de inspección visual. Los datos fueron tratados por medio del análisis de regresión, coeficiente de relación intraclase (CCI), ANOVA com dos factores con test post hoc de Tukey y el test t apareado para alfa < 0,05. Las variaciones intra-observadores e intra-sujetos fueron determinados por medio del error típico (s) y el coeficiente de variación (CV). RESULTADOS: No hubo diferencia significativa entre los tests para el VO2max y el LAn. Não fueron observadas diferencias significativas entre los testeadores para la determinación del LAn. El VO2max presentó entre los dos tests CCI = 0,97, s = ± 0,14 L • min-1 y CV = ± 5,5% y para el LAn el CCI = 0,90, s = ± 0,14 L • min-1, e CV = ± 9,2%. La determinación del LAn interobservadores presentó CCI = 0,95, s = ± 0,10 L • min-1 e CV = ± 5,6%. CONCLUSION: El VO2max y el LAn fueron medidas satisfatoriamente precisas.

Objetividad; Consumo máximo de oxígeno; Umbral de lactato y umbral ventilatorio

ORIGINAL ARTICLE

Accuracy of O_2max and anaerobic threshold determination^*

Paulo Cesar N. Granja Filho; Fernando A.M.S. Pompeu; Alair Pedro Ribeiro de Souza e Silva

^{Correspondence}

ABSTRACT

Studies on the accuracy of the gas exchange and ventilation parameters during exertion involving the Brazilian population are scarce in literature.

OBJECTIVE : To determine the reliability of the maximal oxygen intake (VO_2max) and anaerobic threshold (AnT), as well as the objectivity of the AnT determination in Brazilian healthy youth adults.

METHODS: Two tests of maximal exertion were applied. Two independent observers applied the visual inspection method for the AnT determination. The data were compared by means of the regression analysis, intraclass correlation coefficient (ICC), two-way ANOVA and the paired t-test for an a < 0.05. The intra-observer and intra-subject variabilities were determined by means of the typical error (s) and variation coefficient (VC).

RESULTS: No significant differences between tests for the VO_2max and AnT determination as well as between observers in AnT determination were observed. The new VO_2max presented ICC = 0.97, s = ± 0.14 L • min^-1, and VC = ± 5.5%. The AnT presented ICC = 0.90, s = ± 0.14 L • min^-1, and VC = ± 9.2%. The inter-observers AnT determination presented ICC = 0.95, s = 0.1 L • min^-1 and VC = 5.6%.

CONCLUSION: The VO_2max and the AnT are reliable measurements, and the AnT determination was demonstrated to be an objective method in the population studied.

Key words: Reliability. Objectivity. Maximal oxygen intake. Anaerobic threshold and ventilatory threshold.

INTRODUCTION

The maximum oxygen intake (O_2max) and the aerobic threshold (AnT) are parameters used in the evaluation of the maximum cardiorespiratory function and functional reserve. The O_2max has aided on the selection of candidates for heart transplantation (< 14 mL • kg^-1 • min^-1), once it presents high predictive value with regard to the mortality rate of these patients^(1,2).

The athletic performance in long duration events presents good association (r = 0.78) with O_2max⁽³⁾. However, this phenomenon was not observed in homogeneous groups of high-level athletes^(4,5). Stronger correlations may be found between AnT and the performance in long distance events (r = 0.94 to 0.98)⁽³⁾.

In order to measure these parameters in the clinical and sportive scope, automatic ergospirometers with good temporal resolution are employed. However, the instruments available in most national laboratories are less sophisticated due to their lower cost. These equipments have not been evaluated with regard to the quality of measurements. In this case, Brazilian researchers are limited to extrapolations based on foreign studies performed with sophisticated equipments. Therefore, the objective of the present investigation was to analyze the O_2max and AnT reliability as well as the objectivity of AnT, when equipments widely used in the national territory are employed.

METHODS

Fourteen non-smoker healthy young adults involved in non-competitive physical activities were volunteers in this study: 24 ± 4 years of age, 66.2 ± 13.7 kg and 169.6 ± 10.2 cm. This group was composed of five women (28 ± 6 years of age; 57.2 ± 4.1 kg and 160.2 ± 7.1 cm) and nine men (22 ± 2 years of age, 71.1 ± 14.8 kg and 174.8 ± 7.4 cm). Before tests, all volunteers filled a Cleared and Free Consent Term. The experimental protocol of this study was previously approved by the Ethics Committee for studies involving human beings of the HSE (CEP. 000.021/99). In the day before the examination, the participants were recommended not to perform exhausting physical activities. They were also recommended to avoid caffeine and food three hours before exertion test.

At the first visit to laboratory, the volunteers performed a familiarization test. One week later, the subjects returned to laboratory for the performance of the experimental tests, which were separated by the minimum interval of one and maximum interval of two weeks.

A assigned and continuous protocol⁽⁶⁾ was used, which was composed of initial rest for six minutes sitting on the cycle ergometer (Monark^®, Brazil) followed by a four-minute warm-up exercise with no load and later by the assigned phase with duration of 8-12 minutes. In relation to the increments, the maximum load was calculated (W_max)⁽⁷⁾ and divided into ten parts for the determination of the one-minute stages. The rhythm ranged according to the individual from 60 to 96 rpm and from 15 to 35 W • min^-1.

Gas exchange and ventilation variables were integrated each 20 seconds based on measurements collected through a metabolic analyzer (Aerosport^® TEEM 100, USA) and average-flow pneumotachograph (Hans Rudolph^®, USA). The heart rate was controlled by means of a cardiotachometer (Polar Sport Tester^®, Finland) each five seconds.

The equipments calibration procedures were performed prior to the performance of each test. The ergospirometer was calibrated by means of a standard gas mixture (AGA^®, Brazil) balanced with nitrogen, containing 17.01% of oxygen and 5.00% of carbon dioxide. The outflow was calibrated through a three-liter syringe (Hans Rudolph^®, USA) and the cycle ergometer by means of a 3-kg ballast.

The tests, always performed by the same observer were considered as satisfactory when at least one of the following criteria⁽⁸⁾ for maximum exertion was reached: O₂ plateau (increase < 150 mL • min^-1 or 2 mL • kg^-1• min^-1), HR_max > 180 bpm, Borg > 18 and RER > 1.1. There was no verbal or other external nature encouragement that could change the exertion continuation time.

The AnT determination was performed through the visual inspection method^(6,9-11). To do so, the modified v-slope graphics (V-s mod), the ventilatory equivalents (E/O₂ x time and E/VCO₂ x time), the minute ventilation (VE x time) and the gas exchange ratio (RER x time) were analyzed. Two independent observers de termined the AnT for each subject with the analysis of four graphics all in all (AnT_app). Such observers presented a minimum experience of two years in ergospirometry training. The average of values between both observers was used as combined method⁽¹²⁾ (AnT_comb). The threshold values were expressed as O₂abs (L • min¹), O₂rel (mL • kg^-1 • min^-1) and physical power (watts).

The statistical treatment was conducted through the SPSS^® software for Windows and Excel^® spreadsheet⁽¹³⁾. For the analysis of the O_2max and AnT_comb reliability, the differences between averages were evaluated through the paired t-test. Two two-factor ANOVAs (4 x 4) were used in order to compare graphics for the AnT determination in both tests, or by both observers. The post hoc HSD-Tukey test was applied whenever necessary. The association degree between tests and observers was measured through the intraclass correlation coefficient (ICC). The linear analysis regression was used to establish the load (watts) corresponding to the AnT_comb (L • min^-1) for each subject and yet, to relate O_2max and AnT_comb between both tests. The intra-subject and intra-observer variations were measured through the typical error (s) and through the variation coefficient (VC)⁽¹⁴⁾. The significance level adopted was lower than or equal to 0.05.

RESULTS

The difference between O_2max in both moments (O_2max abs: test A = 3.03 ± 0,81 L • min^-1 and test B = 3.01 ± 0.85 L • min^-1; O_2maxrel: test A = 46.1 ± 9.5 mL • kg^-1 • min^-1 and test B = 45.5 ± 9.7 mL • kg^-1 • min^-1) was not significant. The intra-subjects variation for O_2max was of 0.14 L • min^-1 (VC = 5.5%) or 2.0 mL • kg^-1 • min^-1 (VC = 5.4%). A strong association degree was observed between both tests for the measures of O_2max (O_2maxabs: ICC = 0.97, O_2maxrel: ICC = 0.95).

The differences in the AnT_comb between tests, expressed as O₂abs (test A = 1.55 ± 0.49 L • min^-1 and test B = 1.51 ± 0.42 L • min^-1), as O₂rel (test A = 23.5 ± 5.8 mL • kg^-1 • min^-1 and test B = 22.9 ± 5.5 mL • kg^-1 • min^-1) or as load (test A = 112 ± 35 W and test B = 111 ± 30 W), were not significant. Not significant differences were also observed for the AnT determination through each parameter employed in the visual inspection (table 1). The intra-subject variation for AnT_comb was of 0.14 L • min^-1 (VC = 9.2%) or 2.0 mL • kg^-1 • min^-1 (VC = 8.5%). A strong association was observed between tests for the AnT_comb expressed as O₂abs (ICC = 0.90), as O₂rel (ICC = 0.87) and as load (ICC = 0.80). The association degree between tests and the intra-observer variation for visual inspection methods are presented in table 2.

The difference between observers for methods alone or together (table 1) was not significant. A high association degree of AnT was observed between observers in test A expressed as O₂abs (ICC = 0.92), as O₂rel (ICC = 0.93) and as load (ICC = 0.85). Similar results were also observed in test B when AnT_obs was expressed as O₂abs (ICC = 0.93), as O₂rel (ICC = 0.91) and as load (ICC = 0.90).

DISCUSSION

The combined method for the AnT detection proposed by Gaskill et al.⁽¹²⁾ was based on the averages of intensities determined by independent observers. In order to establish the AnT intensity, these observers employed the visual inspection of three graphics (simplified v-slope, ventilatory equivalents and excess of exhaled CO₂). In this study⁽¹²⁾, a strong association (r² = 0.93, n = 54) between test and retest was demonstrated.

Caiozzo et al.⁽¹⁰⁾ found excellent correlation between tests for the ventilatory equivalents method (r = 0.93). However, this parameter presented lower reproducibility in the tests of Cohen-Solal et al.⁽¹⁶⁾ with cardiac patients (r = 0.83). Davis et al.⁽¹⁷⁾ reported moderate correlation (r = 0.74) between tests for AnT using the visual inspection of three graphics (E x time, FeO₂ x time and CO₂ x time). In the last study⁽¹⁷⁾, as in the current one, the determination of O₂ in AnT was less reliable than when performed through the respiratory exchange ratio method (RER).

Table 2 presents the anaerobic threshold per observer (AnT_obs) using all graphics. One observes that the concurrent employment of all graphics produces lower intra-observer variation when compared to the employment of graphics alone.

Studies on the objectivity of AnT presented conflicting results. Posner et al.⁽¹⁷⁾ found ICC = 0.94 between the best observers, Gladden et al.⁽¹⁸⁾ reported ICC = 0.70 and Shimizu et al.⁽¹⁹⁾, ICC = 0.85.

The time interval between tests and the AnT detection method may present relevant effects in methodological studies. Hopkins⁽²⁰⁾ suggested, based on a meta-analysis, that the optimum interval between tests should be of 2.5 days. This author believes that this period presents no fatigue residue and therefore no alterations in the second test. However, the interval from 7 to 14 days may be operationally more worthwhile, as, according to the experience from our laboratory, this interval improves the adherence to these tests. In intervals of up to two weeks, no significant changes in the performance of individuals who do not participate in training programs are expected.

The influence of the biological variation on the AnT and O_2max reliability is not fully known. Tests as that performed by Katch et al.⁽²¹⁾ tried to measure this variation through multiple tests along the period of four weeks, five days a week in well-trained athletes (n = 5). These authors concluded that the biological variation is equivalent to 90% of all fluctuation of the O_2max results. Interestingly, figure 1 shows that individuals with higher O_2max values are the nearest to the identity line. We believe that the biological variation is lower among the most capable individuals. In addition, one observes that the magnitude of the peripheral and central chronic adaptations observed after training are inversely proportional to the initial conditioning level. Skinner et al.⁽²²⁾ studied 614 individuals and demonstrated that those with lower O_2max presented the highest adaptations (21.9%). In another study⁽¹⁵⁾, the authors demonstrated that tests conducted with well-trained athletes are more accurate than those conducted with sedentary individuals.

The plateau criterion for the O_2max characterization was firstly proposed by Taylor et al.⁽²³⁾ in the middle of the XXth century and since then it was considered as the main reference of maximum exertion. However, in the present study, this criterion was observed in only 41.6% of the tests. A possible explanation for the absence of this phenomenon may be the time employed in the sampling of gases. Myers et al.⁽²⁴⁾ found large variation on the angular coefficient of the relation between O₂ and exertion time when administered several intervals for the collection of gas samples. In this case, the plateau, defined as an inclination smaller than or equal to zero in the O₂, was more affected in shorter intervals. These data suggest that the variation in the O₂ x time relation depends on the gas samples collection interval.

Another possible source of error in the present study may be due to the mechanical-braking cycle ergometer (friction). This type of equipment requires periodic adjustments in the resistance⁽²⁵⁾. This occurs due to the heating of the nylon belt that modifies the friction and hence the resistance⁽²⁵⁾. The intra-observer error in the reading of the load calibrated scale in kp may also present some influence on the AnT_comb variation. Wilmore et al.⁽²⁶⁾ investigated by electronic means the lack of calibration of different cycle ergometers and the effect of this error on the O₂ reliability in several exertion intensities. Those authors observed a variation of approximately 10% in the load of the mechanical-braking cycle ergometer; however, this variation was not sufficient to change the good association (r = 0.88) in the O₂ measurement between two moments at load of 98 W. In the investigation of Wilmore et al.⁽²⁶⁾, the decreasing tendency of correlations with the increase on the work load was also observed. In the present study, the averages of loads corresponding to AnT_comb were found near to those presented in the study mentioned above⁽²⁶⁾ (ICC = 0.80). The reduction on the correlation for O₂ with the increase on the work load may be explained by the lack of calibration of the ergometer and/or ergospirometer.

When AnT_comb was expressed by the work load, a higher variation between both moments was observed (VC = 12.1%) if compared to that expressed by the O₂ (L • min^-1: VC = 9.2%; and as mL • kg^-1 • min^-1: VC = 8.4%). In several studies, VC values from 1.9 to 8.4% for the O_2max were observed^{(21,23,27-29)}. Gerrard et al.⁽²⁹⁾ included the diurnal variation in the treatment of their data. Those authors performed six tests for each subject (3 days x 2 periods) and could observe VC of 8.4% for the O_2max and of 12% for the AnT. Taylor et al.⁽²³⁾ obtained VC = 2.4% using discontinuous protocol and measuring O₂ in the last minute of the test under well-controlled conditions. The subjects' motivation may be an important aspect for the reliability of the O_2max measure⁽³⁰⁾. However, the AnT theoretically should not be affected by motivation, once it occurs within submaximal effort levels.

Due to the Brazilian cultural and socioeconomic conditions, it is possible that the lack of experience with cyclism may have influenced negatively the results obtained. Cyclism produces distinct effects on O_2max in sedentary individuals (generally 5 to 20% lower than that observed in running) and in cyclists (generally 10% higher than that observed in running). In case the subjects had been submitted to treadmill test, a higher reliability would have possibly been obtained.

Cautions in the pre-tests may also have influenced the results. However, the subjects were informed about the importance of non-engaging in physical training programs, once significant changes on AnT are expected (expressed as L • min^-1, but not as %O_2max) in normal men from the third week of training at 80% of the O_2max on, during 30 minutes, four days a week⁽³¹⁾.

Therefore, one concludes that the O_2max and the AnT present small intra-subject, intra-observer and inter-observer variation (in the second case), being precise parameters when the equipments used are those most frequently adopted in national laboratories.

ACKNOWLEDGMENTS

The authors would like to thank the financial support and the priceless academic contribution from AACEA-HSE in the person of Dr. Aluysio S. Aderaldo Jr. They also thank the contribution of academicians Jan B. Bartholomeu and Paulo André da Silva in the data collection phase. Finally, they would like to thank the valuable text revisions by PhD Profs. Martha M. Sorenson and Verônica S. Pinto (Bioqmed/UFRJ).

REFERENCES

Received in 17/12/04. 2^nd version received in 18/1/05. Approved in 12/5/05.

All the authors declared there is not any potential conflict of interests regarding this article.

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*

Departamento de Biociências da Atividade Física EEFD/UFRJ.

Publication Dates

• Publication in this collection
  15 Sept 2005
• Date of issue
  June 2005

History

• Accepted
  12 May 2005
• Received
  17 Dec 2004