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Comparative analysis of predictive formulas for the evaluation of functional capacity with cardiopulmonary test in professional female soccer players

Alexandre Fenley Rafael Santiago Floriano Tiago de Oliveira Chaves Igor Nasser Michel Silva Reis About the authors

RESUMO

Comparar a validade de duas fórmulas de predição do consumo de oxigênio (VO2) com os valores obtidos no teste cardiopulmonar (TCP) em esteira ergométrica de jogadoras de futebol profissional. Dezoito jogadoras de futebol profissional foram submetidas ao TCP em esteira em um protocolo de carga incremental. Na sequência, foi determinado o VO2 da potência do limiar anaeróbio ventilatório (LAV) e no pico do exercício físico. Posteriormente, as fórmulas de predição de VO2 - i) VO2 = (0,2 x velocidade) + (0,9 x velocidade x inclinação) + 3,5 - velocidade em mph e inclinação %); e ii) MET (equivalente metabólica) = 6xHRI-5, onde HRI = frequência cardíaca máxima/frequência cardíaca de repouso - foram aplicadas nas mesmas potências para comparação. Para a primeira fórmula foi observado que tanto no LAV como no pico do TCP, os dados obtidos ficaram abaixo do previsto, sugerindo que a fórmula superestima o VO2 e, consequentemente, a capacidade e a potência aeróbicas. Na segunda fórmula foi observado que os valores ficaram abaixo do obtido, sugerindo que a fórmula subestimou o VO2 e, consequentemente a potência aeróbica, e mais uma vez a capacidade funcional. Diante disso, as fórmulas de predição não mostraram similaridade na determinação da capacidade funcional (CF) de jogadoras de futebol profissional, sugerindo não serem recomendadas para essa população.

Descritores
Teste de Esforço; Mulheres; Futebol

RESUMEN

Comparar la validez de dos fórmulas para predecir el consumo de oxígeno (VO2) con los valores obtenidos en la prueba cardiopulmonar (PCP) en una cinta de correr de jugadoras de fútbol profesionales. Dieciocho jugadoras de fútbol profesional se sometieron al PCP en cinta de correr en un protocolo de carga incremental. En la secuencia, se determinó el VO2 de la potencia del Umbral Anaeróbico Ventilatorio (UAV) y en el pico del ejercicio físico. Posteriormente, las fórmulas de predicción de VO2 -i) VO2 = (0,2 × velocidad) + (0,9 × velocidad × inclinación) + 3,5 − velocidad en mph e inclinación %); y ii) MET (equivalente metabólico) = 6xHRI−5, donde HRI = frecuencia cardiaca máxima/frecuencia cardíaca de reposo- se aplicaron en las mismas potencias para comparación. Para la primera fórmula se observó que tanto en la UAV como en el pico del PCP, los datos obtenidos quedaron por debajo de lo previsto, sugiriendo que la fórmula sobrestima el VO2 y, consecuentemente, la capacidad y la potencia aeróbica. En la segunda fórmula se observó que los valores quedaron por debajo de lo obtenido, sugiriendo que la fórmula subestimó el VO2 y, consecuentemente, la potencia aeróbica, y una vez más la capacidad funcional. Por lo tanto, las fórmulas de predicción no mostraron semejanza en la determinación de la capacidad funcional (CF) de las jugadoras de fútbol profesional, sugiriendo que no son recomendadas para esa población.

Palabras clave
Prueba de Esfuerzo; Mujeres; Fútbol

ABSTRACT

To compare the validity of two oxygen consumption (VO2) prediction formulas with the values obtained through cardiopulmonary exercise test (CPT) in a treadmill with professional female soccer players. Eighteen professional female soccer players performed CPT in a treadmill with an incremental protocol. The VO2 of the gas exchange threshold (GET) was determined, as well as at peak exercise. After that, the following formula of VO2prediction i) VO2 = (0.2 x velocity) + (0.9 x velocity x incline) + 3.5 - velocity, in mph and %incline); and ii) MET (metabolic equivalent) = 6xHRI-5, where HRI = maximum heart rate/resting heart rate, were applied in the same power for comparison. In the first formula, the values obtained in GET and at peak exercise were below the estimated, indicating that the formula overestimated VO2 and, consequently, aerobic capacity and power. In the second formula, the values were below the estimated, indicating that the formula also underestimated VO2 and, consequently, aerobic capacity and power. Given these results, the prediction formulas do not present similarity in determining the functional capacity (FC) of professional female soccer players, indicating they are not suitable for this population.

Keywords
Exercise Test; Women; Soccer

INTRODUCTION

Functional capacity (FC) is the ability to perform daily routine activities independently. This component has been used for disease diagnosis, risk stratification and prescription of exercises11. Kodama S, Saito K, Tanaka S, Maki M, Yachi Y, Asumi M, et al. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. 2009;301(19):2024-35. doi: 10.1001/jama.2009.681
https://doi.org/10.1001/jama.2009.681...
. Given this scenario, strategies have been proposed for the implementation of assessment methods and for obtaining FC.

Among these various strategies, cardiopulmonary exercise testing (CPET) is considered the gold standard for determining FC, aerobic capacity, and aerobic power. The variables obtained allow for the identification of peak VO2 and/or maximum, as well as metabolic thresholds (ventilatory anaerobic threshold - VAT), and respiratory compensation point - RCP), as well as the understanding of limited effort22. Balady GJ, Arena R, Sietsema K, Myers J, Coke L, Fletcher GF, et al. Clinician's guide to cardiopulmonary exercise testing in adults: a scientific statement from the American Heart Association. Circulation. 2010;122(2):191-225. doi: 10.1161/CIR.0b013e3181e52e69
https://doi.org/10.1161/CIR.0b013e3181e5...
. However, the equipment required for the conducting CPET are expensive and require trained staff. In addition, the environment requires specific care such as: control of temperature, humidity, barometric pressure and noise, in order to carry out the protocol in the most appropriate way possible. Given this, there are few places that specialize in this kind of exam and have all the technological tools necessary to perform the CPET33. Neder JA, Nery LE. Fisiologia clínica do exercício: teoria e prática. São Paulo: Artes Médicas; 2003..

On the other hand, there are already described formulas for the prediction of VO2 during exercise in different ergometer and field tests44. Dourado VZ. Reference equations for the 6-minute walk test in healthy individuals. Arq Bras Cardiol. 2011;96(6):1-11. doi.org/10.1590/S0066-782X2011005000024
https://doi.org/10.1590/S0066-782X201100...
), (55. Schubert MM, Washburn RA, Honas JJ, Lee J, Donnelly JE. Exercise volume and aerobic fitness in young adults: the midwest exercise trial-2. SpringerPlus. 2016;5(183):1-9. doi: 10.1186/s40064-016-1850-0
https://doi.org/10.1186/s40064-016-1850-...
. However, little is known about the application of these formulas in specific populations, and the available data do not allow to extrapolate their validity for different groups. Thus, the objective of this study is to compare two formulas for the prediction of VO2, using the VO2 obtained through CPET during VAT and at peak exercise in professional soccer players.

METHODOLOGY

Sample

Prospective, observational and cross-sectional study A convenience sample of 18 professional female soccer players was selected. The athletes should meet the following inclusion criteria: age older than 18 years, healthy according to clinical evaluation and, finally, training regularly with their team with minimum frequency of five times per week. The clinical evaluation was performed by the doctor responsible for the team, and routine exams were conducted to assist in the exclusion of diseases, such as: laboratory tests (complete blood count, biochemistry, electrolytes) and electrocardiogram. Players with a history of cardiovascular, respiratory, neurological, orthopedic, muscular, immune or metabolic disease were excluded. This study was approved by the Ethics Committee of the Clementino Fraga Filho University Hospital, in accordance with Resolution No. 466/2012 (CAAE: 43656115.8.0000.5257). All volunteers signed the Informed Consent Form to participate in this study.

Maximum or symptom-limited cardiopulmonary exercise test

The test was performed in an air-conditioned laboratory with temperature between 22° C and 24° C and relative humidity between 50% and 60%, at the same period in the morning. The volunteers were familiar with the experimental environment and the experimenters. The CPET associated with the ergometric system aimed to evaluate the functional capacity of the athletes and identify possible electrocardiographic and hemodynamic changes caused by exercise that may contraindicate their participation in the study. In addition, the protocol adopted for conducting CPET was of type ramp on ergometric treadmill (Inbrasport Master Super ATL, Porto Alegre, RS, Brazil). Initially, the volunteers stayed two minutes at rest on the treadmill; afterwards began a warm-up period for three minutes, walking at 2 km/h and without incline. After this step, the exercise protocol was initiated with increments of 1 km/h per minute and set 1% slope, according to prior study protocol6 until physical exhaustion - that is, the impossibility of the volunteer to run the load imposed by the ergometric treadmill. Load distribution was controlled through the measurement system of ventilatory and metabolic variables (VO2000 - Portable Medical Graphics Corporation, USA). Finally, the post-test recovery period consisted of three minutes at submaximal speed (3 km/h) without inclination, followed by two minutes of rest and sitting after interruption of the load.

Ventilatory and metabolic variables as well as heart rate (HR) were captured and recorded throughout the whole test period, as described below. The peripheral oxygen saturation - SpO2 (Onyx 9500®, Uberlândia, MG, Brazil) - and the electrocardiogram - ECG (Wincardio USB, Micromed, Brasília, DF, Brazil) - in the derivations MC5, DII, DIII, aVR, aVL, and aVF modified as well as in V1 to V6 were continuously monitored during the whole experimental procedure. Blood pressure was verified in certain periods of the protocol, taking care to avoid interference in the collection of variables. It is worth mentioning that all tests were conducted by a research team composed of physiotherapists and doctors, who were attentive to the signs and/or symptoms of inadequate response to exercise. In addition, the ventilatory and metabolic variables were obtained by means of computerized system of ergospirometric analysis (VO2000 - Portable Medical Graphics Corporation, USA). Current volume was obtained through a Pitot pneumotachometer connected to the VO2000 system and attached to a face mask - selected according to the face size of the volunteer in order to be properly adjusted, preventing air leaks. After fitting the mask, a few minutes passed until the ventilation of the volunteers stabilized. The equipment provided VO2 respiration, carbon dioxide elimination (VCO2), pulmonary ventilation (VE), HR and SpO2 values in real time. The values of ventilatory equivalents of oxygen (O2) (VE/VO2) and ventilatory equivalents of VCO2 (VE/VCO2), as well as the ratio of respiratory exchanges (R), the final expired fraction of O2 (FEO2), the final expired fraction of CO2 (FECO2), current volume (CV) and respiratory rate (RR) were also calculated and stored.

Data analysis: determining VAT and peak VO2

For determining VAT, the V-slope method was adopted, using the curves of the correlation between VO2 and VCO2. Subsequently, the relationship between VO2 and VE/FEO2 plotted as a function of time was also used for determining VAT. For this, three independent observers conducted VAT determination in the following situations66. Wasserman K, Sue DY, Stringer WW, Sietsema KE, Xing-Guo S, et al. Principles of exercise testing and interpretation. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2005.: 1) VE/VO2: lowest value of this relationship, ensuring that, from it, systematic increase occurs (point of highest ventilatory efficiency); 2) FEO2: lowest value of this variable, from which begins a systematic increase.

The analysis section selected was based on the responses of cardiorespiratory variables, that is, from the moment they start responding to the increased intensity up to the interruption of the exercise. The qualitative control of the experiment was conducted by means of various criteria: presence or not of equilibrium in the heating stage; whether the beginning of HR responses and ventilatory variables coincided with the increase in intensity; and whether ventilatory variables showed linear behavior at the beginning of the ramp. This method was used as gold standard in the comparisons with other methods for determining VAT. Finally, to identify peak VO2, an average of the last 30 seconds of the ramp protocol during CPET was calculated.

Prediction of VO2

For indirect determination of VO2, two formulas were used for prediction. The first was described as VO2 = (0.2 x speed) + (0.9 x speed + incline) + 3.5 - speed in mph and incline in %. This strategy for prediction of functional capacity was proposed by the American College Of Sports Medicine (ACSM) (77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
, and has been a reference for the prescription and interpretation of the most frequently used exercise test results. The second strategy for determining FC was derived from a meta-analysis of 60 studies about direct determination of oxygen consumption in ergometric treadmill at peak exercise. The equation was described as: MET (metabolic equivalent) = 6x heart rate index (HRI), - 5, where HRI=Maximum HR/resting HR88. Wicks JR, Oldridge NB. How accurate is the prediction of maximal oxygen uptake with treadmill testing? PLoS ONE. 2016;11(11):1-13. doi: 10.1371/journal.pone.0166608
https://doi.org/10.1371/journal.pone.016...
.

Statistical analysis

Initially, the data were submitted to a normality test (Kolmogorov-Smirnov test) and a homogeneity test (Levene test). When appropriate, the paired Student’s t test was applied for parametric variables. General characteristics and those of CPET were expressed as mean ± standard deviation. The significance level was p<0.05 and the analyses were performed with the software SigmaPlot for Windows, version 11.0 (copyright© 2008 Systat Software, Inc).

RESULTS

Table 1 presents the characteristics of the study population. The volunteers were young and eutrophic.

Table 1
General characteristics of the volunteers studied

Table 2 presents the respiratory and metabolic variables obtained from the CPET at peak and in VAT. The HR that was obtained of dyspnea and lower limbs at peak exercise (102% of maximum HR, as stated in the Karvonen formula), according to the Brazilian Society of Cardiology99. Godoy Y, editor. I Consenso Nacional de Reabilitação Cardíaca. Arq Bras Cardiol. 1997;69(4):267-91. and the rating of perceived exertion, the Borg Scale1010. Borg GA.Psychophysical bases of perceived exertion.Med Sci Sports Exerc. 1982;14(5):377-81., was compatible with that of high intensity exercises, indicating that the test lead to the exhaustion of the volunteers. According to the value of the relative peak VO2, the volunteers presented regular aerobic capacity that was in accordance with the classification of the American Heart Association (AHA) (66. Wasserman K, Sue DY, Stringer WW, Sietsema KE, Xing-Guo S, et al. Principles of exercise testing and interpretation. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2005..

Table 2
Respiratory and metabolic variables obtained from maximum and/or symptom-limited cardiopulmonary exercise testing at peak exercise.

Figure 1 presents the relative VO2 obtained through CPET and the expected through the ACSM77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
) formula. Both with the VAT and peak of CPET, the data obtained were below the expected, suggesting that the formula overestimates VO2 and, consequently, aerobic capacity and power.

Figure 1
Obtained and expected oxygen consumption (VO2) according to the American Heart Association66. Wasserman K, Sue DY, Stringer WW, Sietsema KE, Xing-Guo S, et al. Principles of exercise testing and interpretation. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2005. (AHA) for the volunteers analyzed. (A): ventilatory anaerobic threshold; (B): peak of cardiopulmonary exercise testing. Paired Student’s t-test with p<0.05.

Figure 2 presents the MET88. Wicks JR, Oldridge NB. How accurate is the prediction of maximal oxygen uptake with treadmill testing? PLoS ONE. 2016;11(11):1-13. doi: 10.1371/journal.pone.0166608
https://doi.org/10.1371/journal.pone.016...
prediction formula, when compared with the MET corresponding to the VO2 obtained at peak exercise. It was observed that the prediction formula was below the result obtained, suggesting that it underestimated VO2 and, consequently, aerobic power.

Figure 2
Obtained and expected metabolic equivalent by the formula MET88. Wicks JR, Oldridge NB. How accurate is the prediction of maximal oxygen uptake with treadmill testing? PLoS ONE. 2016;11(11):1-13. doi: 10.1371/journal.pone.0166608
https://doi.org/10.1371/journal.pone.016...
at peak exercise of the volunteers. Paired Student’s t-test with p<0.05.

DISCUSSION

The main findings of our study were: i) for the ACSM77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
) formula, both in VAT and at the peak CPET the data overestimated VO2 and, consequently, aerobic capacity and power; ii) for the MET formula at peak CPET, the data underestimated VO2 and, consequently, aerobic power. Given this scenario, the relevance of our study is in testing two stratification formulas of aerobic power and capacity, where that of ACSM77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
was the most widely adopted and the MET88. Wicks JR, Oldridge NB. How accurate is the prediction of maximal oxygen uptake with treadmill testing? PLoS ONE. 2016;11(11):1-13. doi: 10.1371/journal.pone.0166608
https://doi.org/10.1371/journal.pone.016...
formula the most current proposal for physical fitness assessment and prescription of physical exercises.

The volunteers were young, eutrophic, healthy and had a training routine that combined physical and tactical preparation. In addition, they participated annually from two professional championships (Campeonato Brasileiro de Futebol and Campeonato Carioca de Futebol). However, interestingly, the players presented an obtained VO2 peak at peak CPET below the estimated for high performance athletes, which classified them as having regular physical fitness77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
. Such findings seem to suggest that the peak VO2 response of the athletes may be related to two factors: i) position in the field, as defenders and strikers travel, during a 90 minute game, a distance lower than that traveled by midfielders and left back1111. Sousa RB, Praça GM, Greco PJ. Avaliação de jogadores de futebol: relação entre a capacidade aeróbica e eficácia tática. RBFF. 2017;9(33):190-6., justifying lower VO2 values; and ii) tactical training and physical preparation specific to each position1212. Balikian P, Lourenção A, Ribeiro LFP, Festuccia WTL, Neiva CM. Maximal oxygen uptake and anaerobic threshold in professional soccer players: comparison between different positions. Rev Bras Med Esporte. 2002;8(2):32-6. doi.org/10.1590/S1517-86922002000200002
https://doi.org/10.1590/S1517-8692200200...
.

During pre-season, usually professional players are subjected to cardiorespiratory and performance assessments1313. Fessi MS, Zarrouk N, Filetti C, Rebai H, Elloumi M, Moalla W. Physical and anthropometric changes during pre- and in-season in professional soccer players. J Sports Med Phys Fitness. 2016;56(10):1163-70.. Among these tests, obtaining VO2 has been of particular importance for the stratification of fitness and physical preparation, as it is a factor for determining aerobic capacity. In this way, the use of formulas for VO2 prediction has been attractive as a substitute to CPET, as CPETs are restricted to elite clubs.

In this study, the ACSM7 formula was shown not to be adequate to reflect the aerobic capacity and power of athletes. Some factors may have compromised the sensitivity of this tool. The first aspect to be considered is the application of only two variables, which may be little sensitive to reflect the population studied (speed and incline of the treadmill). The second aspect refers to mechanical efficiency, since, depending on the population studied, the pass may be influenced by height and body mass, leading the volunteers to adapt their center of mass at the imposed speed (adopting short or long passes) (1414. Levy WC, Maichel BA, Steele NP, Leclerc KM, Stratton JR. Biomechanical efficiency is decreased in heart failure during low-level steady state and maximal ramp exercise.Eur J Heart Fail. 2004;6(7):917-26. doi: 10.1016/j.ejheart.2004.02.010
https://doi.org/10.1016/j.ejheart.2004.0...
Another aspect that must be considered is that, as it is developed for patients with cardiovascular disease, central dysfunction and, potentially, the presence of peripheral muscle dysfunction (common in heart conditions) (1515. Reis HV, Borghi-Silva A, Catai AM, Reis MS. Impact of CPAP on physical exercise tolerance and sympathetic-vagal balance in patients with chronic heart failure. Braz J Phys Ther. 2014;18(3):218-27. doi.org/10.1590/bjpt-rbf.2014.0037
https://doi.org/10.1590/bjpt-rbf.2014.00...
, the level of these dysfunctions may have influenced in the performance of patients evaluated for the elaboration of the ACSM7 formula.

Another noteworthy consideration is the type of protocol used, since faster incrementing protocols - ramp type - can determine higher speed and inclination values when compared to slower protocols - step type1616. Pithon KR, Martins LE, Gallo JR, Catai AM, Silva E. Comparação das respostas cardiorrespiratórias entre exercício de carga constante e incremental abaixo, acima e no limiar de anaerobiose ventilatório. Rev Bras Fisioter. 2006;10(2):163-9. doi.org/10.1590/S1413-35552006000200005
https://doi.org/10.1590/S1413-3555200600...
. Finally, another doable and relevant aspect is the presence of arm support on the treadmill. It has been shown that performing an exercise Protocol with frontal or lateral support can change metabolic demand and adaptation to the treadmill. This also occurs for the evaluated executing the protocol with free arms1717. Pinkstaff S, Peberdy MA, Kontos MC, Fabiato A, Finucane S, Arena R. Overestimation of aerobic capacity with the Bruce treadmill protocol in patients being assessed for suspected myocardial ischemia. J Cardiopulm Rehabil Prev. 2011;31(4):254-60. doi: 10.1097/HCR.0b013e318211e3ed
https://doi.org/10.1097/HCR.0b013e318211...
.

Regarding the MET88. Wicks JR, Oldridge NB. How accurate is the prediction of maximal oxygen uptake with treadmill testing? PLoS ONE. 2016;11(11):1-13. doi: 10.1371/journal.pone.0166608
https://doi.org/10.1371/journal.pone.016...
formula, in spite of the systematic review that considered using maximal and resting HR an advantage as opposed to formulas that apply speed and incline on the treadmill (such as ACSM), this study showed that the aerobic power of the athletes was underestimated. Two aspects should be considered for the application of the index: i) as most studies developing the formula were developed based on cardiac patients, the effect of the medication used (for example, β-blocker) may have influenced in the obtaining of resting HR1818. Goldsmith RL, Bigger JT, Bloomfield DM, Krum H, Steinman RC, Sackner-Bernstein J, Packer M. Long-term carvedilol therapy increases parasympathetic nervous system activity in chronic congestive heart failure. Am J Cardiol. 1997;80(8):1101-4. doi.org/10.1016/S0002-9149(97)00616-4
https://doi.org/10.1016/S0002-9149(97)00...
; and ii) it is logic to think, as has been established in the literature, that HR is lower in athletes with regular physical training routine1919. Hsu CY, Hsieh PL, Hsiao SF, Chien MY. Effects of exercise training on autonomic function in chronic heart failure: systematic review. BioMed Res Int. 2015;2015(ID 591708):1-8. doi: 10.1155/2015/591708
https://doi.org/10.1155/2015/591708...
. Given these aspects, and the fact that the players selected for this study are of professional level, we can assume that resting HR may have been the variable that explains the underestimation of aerobic power.

On the above, it is worth reflecting on the possibility of elaborating a formula that involves more variables, taking into account the expected FC of the population studied. In this respect, it is possible to assume that variables showing the individual skills of the players could be more suitable for VO2 differentiation with regards to field position. This way, it would be possible to evaluate in-field movement of professionals in official games or training through devices of type pedometer, global position system (GPS) or laser cameras2020. Doncaster G, Unnithan V. Between-game variation of physical soccer performance measures in highly trained youth soccer players. J Strength Cond Res. 2017(in press). doi: 10.1519/JSC.0000000000002132
https://doi.org/10.1519/JSC.000000000000...
, which could provide prediction equations with data. Another commonly used strategy in physical training of athletes are field tests. They are able to provide more individualized information on performance of players and could subsidize new formulas for FC prediction. A very applied test in the football world has been the YoYo test, which is able to determine VO22121. Krustrup P, Mohr M, Amstrup T, Rysgaard T, Johansen J, Steensberg A, et al. The yo-yo intermittent recovery test: physiological response, reliability, and validity. Med Sci Sports Exerc. 2003;35(4):697-705. doi: 10.1249/01.MSS.0000058441.94520.32
https://doi.org/10.1249/01.MSS.000005844...
using the distance traveled.

According to another research2222. Magrani P, Pompeu FAMS. Equations for predicting aerobic power (VO2) of young Brazilian adults. Arq Bras Cardiol. 2010;94(6):763-70. doi.org/10.1590/S0066-782X2010005000054
https://doi.org/10.1590/S0066-782X201000...
, when comparing predictive models with formulas already described in the literature, such as ACSM77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
or the formulas advocated by other authors33. Neder JA, Nery LE. Fisiologia clínica do exercício: teoria e prática. São Paulo: Artes Médicas; 2003., it was shown that VO2 could be accurately predicted using body mass index, age and workload as independent variables, when the volunteers are seemingly healthy and not athletes. In another study2323. Almeida AE, Stefani CM, Nascimento JA, Almeida NM, Santos AC, Ribeiro JP, et al. An equation for the prediction of oxygen consumption in a Brazilian population.Arq Bras Cardiol. 2014;103(4):299-307. doi: 10.5935/abc.20140137
https://doi.org/10.5935/abc.20140137...
, the authors developed an equation for the Brazilian population that takes into account the following variables: gender, age, BMI and physical activity level, comparing it with formulas used in the prediction of VO2, as that of previous studies66. Wasserman K, Sue DY, Stringer WW, Sietsema KE, Xing-Guo S, et al. Principles of exercise testing and interpretation. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2005.), (77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
), (2424. Jones NL, Campbell EJ. Clinical exercise testing. Philadelphia: Saunders; 1982.. The results indicated that both formulas overestimated the VO2 when compared to the equation presented by them. In addition, the authors cite BMI as an imprecise variable, however, better applied to the formula than body weight and height, separately. This fact may have implications on the overestimation in VO2 prediction.

It is worth noting some limitations of the study: i) little cooperation of athletes, making it impossible to present field test data; ii) lack of appropriate formulas for the population studied; iii) small number of volunteers, which may have influenced VO2 values.

CONCLUSION

The FC prediction formulas showed no similarity in determining the aerobic power and capacity of professional female soccer players. In this sense, the ACSM77. Gibbons RJ, Balady GJ, Beasley JW, Bricker JT, Duvernoy WF, Froelicher VF, et al. ACC/AHA guidelines for exercise testing: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines (Committee on Exercise Testing). Circulation. 1997;96(1):345-54. doi: https://doi.org/10.1161/01.CIR.96.1.345
https://doi.org/10.1161/01.CIR.96.1.345...
formula was shown to overestimate VO2 in VAT and at peak exercise, compared to CPET. On the other hand, the prediction formula based on MET88. Wicks JR, Oldridge NB. How accurate is the prediction of maximal oxygen uptake with treadmill testing? PLoS ONE. 2016;11(11):1-13. doi: 10.1371/journal.pone.0166608
https://doi.org/10.1371/journal.pone.016...
was shown to underestimate VO2.

AKNOWLEDGEMENTS

The authors thank Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro - Faperj (process: E-26/110.878/2013) and the National Council for Scientific and Technological Development - CNPq (process: 487.375/2012-2) for the financial support. Additionally, we thank the members of the Research Group for Cardiopulmonary Evaluation and Rehabilitation (Gecare) of the Department of Physical Therapy of the Federal University of Rio de Janeiro (UFRJ).

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  • Study conducted at the Federal University of Rio de Janeiro (UFRJ)
  • Funding source: Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (Faperj) and the National Council for Scientific and Technological Development (CNPq)
  • Approved by the Research Ethics Committee of Clementino Fraga Filho University Hospital under opinion nº 43656115.8.0000.5257.

Publication Dates

  • Publication in this collection
    Jul-Sep 2018

History

  • Received
    20 Feb 2018
  • Accepted
    17 May 2018
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