IJCS | Volume 31, Nº4, July / August 2018

327 de Souza e Silva et al. Cardiorespiratory optimal point in soccer players Int J Cardiovasc Sci. 2018;31(4)323-332 Original Article Cont. Table 1 - Major demographic characteristics and results of maximal cardiopulmonary exercise test on treadmill of professional soccer players Variables* Total (n = 198) Goalkeeper (n = 13) Left/right-back (n = 27) Center-defender (n = 32) Midfielder (n = 76) Forwarder (n = 50) p value VO 2 at the COP (mL.kg -1 .min -1 ) 31.8 (29.0 - 34.6) 33.6 (31.0 - 33.7) 32.2 (28.6 - 35.7) 33.1 (30.9 - 35.6) 31.3 (28.2 - 34.4) c 31.3 (33.8 - 29.7) c 0.10 %VO 2 max at the COP 51.4 (46.4 - 55.8) 57.0 (53.3 - 59.3) 48.4 (45.1 - 54.7) 55.9 (51.2 - 59.2) $ 51.0 (44.2 - 54.3) ß 50.7 (45.9 - 54.0) ß ,# < 0.01 Time to reach the VT (min) 7.9 ± 1.4 8.1 ± 0.9 8.1 ± 1.3 7.3 ± 1.3 b 8.0 ± 1.6 c 7.8 ± 1.3 0.06 Velocity at the VT (km.h -1 ) 14.3 ± 1.1 14.5 ± 0.7 14.5 ± 1.0 13.8 ± 1.1 b 14.4 ± 1.2 c 14.3 ± 1.0 0.06 HR at the VT (bpm) 169 (160 - 178) 178 (168 - 181) 165 (162-169) a 172 (160 - 178) b 167 (160 - 177) a 166 (160 - 178) a 0.08 VO 2 at the VT (mL.kg -1 .min -1 ) 46.8 ± 5.0 45.3 ± 2.5 47.9 ± 4.7 45.5 ± 4.5 46.7 ± 6.1 47.4 ± 4.0 0.25 %VO 2 max at the VT 75.5 ± 5.7 77.3 ± 4.3 74.7 ± 4.8 76.1 ± 6.3 74.7 ± 6.2 76.0 ± 5.4 0.42 VO 2 max (L.min -1 ) 4.75 ± 0.52 4.98 ± 0.35 4.74 ± 0.35 4.82 ± 0.43 4.63 ± 0.60 a 4.81 ± 0.53 0.09 VO 2 max (mL.kg -1 .min -1 ) 62.1 ± 6.2 58.6 ± 3.6 64.2 ± 6.5 59.8 ± 4.8$ 62.6 ± 6.8 ß 62.5 ± 5.8 ß ,# 0.01 * Data expressed as median (interquartile range) or mean ± standard deviation according to the distribution of the variables. The results were compared by use of the unpaired Student t test, ANOVA, Mann-Whitney test, Kruskal-Wallis test or chi-square test, according to the characteristics of the variables. $ No statistically significant difference as compared to the goalkeeper group (p > 0.05). # No statistically significant difference as compared to the midfielder group (p > 0.05). ß No statistically significant difference as compared to the left/right-back group. € No statistically significant difference as compared to the center- defender group. a There was a statistically significant difference as compared to the goalkeeper group (p < 0.05). b There was a statistically significant difference as compared to the left/right-back group (p < 0.05); c There was a statistically significant difference as compared to the center-defender group (p < 0.05). FVC: forced vital capacity; HR: heart rate; VT: ventilatory threshold; SBP: systolic blood pressure; DBP: diastolic blood pressure; COP: cardiorespiratory optimal point; RER: respiratory exchange rate; CPX: cardiopulmonary exercise test; VE: ventilation; FEV1: forced expiratory volume in the first second; VO 2 max: maximal oxygen consumption. of the cardiorespiratory interaction of both healthy individuals and those with chronic diseases; in addition, by being a submaximal variable of CPX, the use of COP is particularly interesting for patients unable to achieve a maximal CPX because of functional limitations (eg, peripheral obstructive arterial disease, orthopedic disorders) or because of their fear of achieving peak exertion (eg, patients with panic syndrome), 17,21 as well as for athletes during the competition season. 22 For example, the COP bears an inverse relationship with all- cause mortality in healthy and ill individuals aged from 40 to 85 years, having, thus, prognostic value and being a new possibility for mortality risk assessment. 17 Based on those observations, it is worth trying to expand the applicability of COP to other scenarios. In theory, one might assume that for athletes of modalities with high aerobic demands, such as soccer, low COP values can represent a physiological advantage, especially when occurring at relatively high velocities. Because the aerobic demands vary according to the field position during the match, the opportunity to compare a large number of elite soccer players tested in standard conditions can contribute to better understand the meaning and the potential applicability of COP in sports. The present study is an original contribution because it is the first to describe the COP behavior in athletes, in particular, high-level adult soccer players submitted to a CPX on a treadmill following the ramp protocol. The COP has advantages related to its determination and measurement when compared to VO 2 max and VT, the two major variables of CPX used to assess the performance of athletes. Obtaining a true VO 2 max