IJCS | Volume 31, Nº4, July / August 2018

324 de Souza e Silva et al. Cardiorespiratory optimal point in soccer players Int J Cardiovasc Sci. 2018;31(4)323-332 Original Article training. 4-6 For example, soccer players with higher VO 2 max are known to cover longer distances during a match, 7 and their mean exercise intensity during the match is approximately 75% of their VO 2 max, similarly to the VT level of those players. 7,8 However, limitations such as low reproducibility, different techniques and criteria for identification of both VO 2 max and VT 9-13 hinder their routine use. In addition, mistakes in such measurements can jeopardize the planning of individualized trainings, impairing the athlete’s performance improvement. 14 In 2012, Ramos et al. 15 showed the minimum value of the ventilatory equivalent for oxygen (minimum VE/ VO 2 ) during a CPX – the cardiorespiratory optimal point (COP) – and described its behavior, which, theoretically, represents the point of the best association or integration between the respiratory and cardiovascular systems. Based on the assessment of more than 600 healthy and non-athletes individuals aged aged between 23 and 73 years, those authors showed that COP tends to be higher in women and increases with age. In addition, studies conducted by that same group have shown that COP measurement is easy, objective and stable in CPX performed in adults, 16 supporting its potential use in physiological research and in clinical practice. Similarly to VO 2 max and VT, COP proved to be an excellent predictor of all-cause mortality in healthy and unhealthy individuals aged between 40 and 85 years. 17 So far, the behavior of COP in athletes is unknown. Thus, our objectives are: a) to describe the behavior of COP in professional soccer players; and b) to assess its association with VO 2 max and VT. Materials and Methods Sample This study analyzed retrospectively the data of 247 soccer players of the major team of a Rio de Janeiro club of the Brazilian Soccer Championship A series, who underwent amaximal CPX at a private Exercise and Sports Medicine clinic between January 2005 andDecember 2016. Of those, 198 players concomitantlymeeting the following inclusion criteria were selected: a) to have undergone a treadmill CPX; b) to have completed a trulymaximal CPX, which was not interrupted due to clinical reasons or lack of motivation; c) to have no history of cardiorespiratory diseases. Based on the information provided by the soccer players, they were categorized according to their predominant field positions: goalkeeper, center-defender, left/right-back, midfielder and forwarder. Assessment protocol Clinical assessment Included clinical history and physical examination, as well as anthropometric, spirometric and resting 12-lead electrocardiographic data. Resting spirometry test At least three maneuvers were carried out to determine the flow-volume curves using a pneumograph (SP-1 Spirometer, Schiller, Switzerland or KoKo, United States) periodically calibrated according to the protocol recommended by the North American and European guidelines. 18 Maximal cardiopulmonary exercise test The CPXwere performed on a treadmill (ATLMaster, Inbramed, Brazil) in a properly climatized room. All players underwent the same ramp protocol, at an initial velocity of 8.0 km.h -1 , with progressive increase of 0.1 km.h -1 every 7.5 seconds, andwithout any inclination. All CPX were conducted by specialized physicians with large experience in assessing athletes, following a well- defined routine, mainly regarding the stimulus to achieve truly maximal exertion. CPX was considered maximal based on the physician’s subjective assessment and other objective variables, such as: occurrence of VT, U-pattern ventilatory equivalent, and a 10-score in the 0-10 Borg scale. 19 During the CPX, the players were monitored continuously by use of a digital electrocardiograph (ErgoPC Elite versions 3.2.1.5 or 3.3.4.3 or 3.3.6.2, Micromed, Brazil), which measured heart rate (HR) on the electrocardiographic tracing in the CC5 or CM5 leads at the end of every minute. Analysis of the expired gases During the CPX, the expired gases were collected by use of a Prevent pneumograph (MedGraphics, United States) coupled to a mouth piece, with concomitant use of a nose clip. The expired gases were measured and analyzed with the VO2000 metabolic analyzer (MedGraphics, United States), whichwas calibratedwith a 2L-serinje and with gases of known concentrations before the first assessment of the day, and this procedure was repeated when necessary. Pulmonary ventilation