Cardiorespiratory Optimal Point in Professional Soccer Players: A Novel Submaximal Variable During Exercise

Abstract Background: Maximal oxygen consumption (VO2max) and ventilatory threshold (VT) obtained during a cardiopulmonary exercise test (CPX) are used in the evaluation of athletes. However, the identification of these variables may sometimes be unreliable, which limits their use. In contrast, the cardiorespiratory optimal point (COP) is a submaximal variable derived from CPX with objective measurement and prognostic significance. However, its behavior in athletes is unknown. Objective: To describe the behavior of COP in professional soccer players and its association with VO2max and VT. Methods: VO2max, VT and COP were obtained retrospectively from 198 soccer players undergoing maximal treadmill CPX using ramp protocol. COP was defined as the lowest value of the ventilation/oxygen consumption ratio in a given minute of the CPX. The soccer players were stratified according to their field position: goalkeeper, center-defender, left/right-back, midfielder and forwarder. Continuous variables were compared using unpaired Student t test or ANOVA, or Mann-Whitney test or Kruskal-Wallis test depending on their distribution, and categorical variables were compared using chi-square test. Pearson correlation was used to test the association between COP and other ventilatory variables. A level of 5% was used for statistical significance. Results: COP (mean ± SD) was 18.2 ± 2.1 and was achieved at a speed 4.3 ± 1.4 km.h-1 lower than that achieved at the VT. While VO2max (62.1 ± 6.2 mL.kg-1.min-1) tended to be lower in goalkeepers (p < 0.05), the COP did not vary according to field position (p = 0.41). No significant association was observed between COP and VO2max (r = 0.032, p = 0.65) or between COP and VT (r = -0.003, p = 0.96). Conclusion: COP can be easily determined during submaximal exercise performed with incremental speed in soccer players and does not vary according to the athlete’s field position. The absence of association with VO2max and VT indicates that COP provides distinct and complementary information to these variables. Future studies are needed to determine the practical implications of COP in assessing athletes. (Int J Cardiovasc Sci. 2018; [online].ahead print, PP.0-0)

研究背景：心肺运动试验（cardiopulmonary exercise test, CPX）中测得的最大摄氧量（maximal oxygen consumption, VO2max）与通气阈值（ventilatory threshold, VT）常用于运动员机能评估，但上述指标的识别有时可靠性不足，限制了其应用价值。与之相对，心肺最优点（cardiorespiratory optimal point, COP）是一种由CPX衍生出的亚最大运动指标，具备客观可测性与预后价值，但其在运动员群体中的表现特征尚不明确。研究目的：描述职业足球运动员的心肺最优点特征，并分析其与最大摄氧量、通气阈值的相关性。研究方法：回顾性分析198名接受采用斜坡递增负荷方案的跑台心肺运动试验的职业足球运动员数据，提取其最大摄氧量、通气阈值与心肺最优点。心肺最优点定义为心肺运动试验中任意一分钟内的通气量与摄氧量比值的最小值。根据场上位置将运动员分为守门员、中后卫、左右边后卫、中场球员与前锋。针对连续变量，根据其数据分布特征分别采用独立样本t检验、单因素方差分析、曼-惠特尼U检验或克鲁斯卡尔-沃利斯H检验进行组间比较；分类变量则采用卡方检验进行比较。采用Pearson相关分析检验心肺最优点与其他通气指标的相关性，统计学显著性阈值设定为5%。研究结果：心肺最优点的均值±标准差为18.2±2.1，其对应的运动速度较通气阈值对应的运动速度低4.3±1.4 km·h⁻¹。守门员的最大摄氧量（62.1±6.2 mL·kg⁻¹·min⁻¹）整体显著偏低（p<0.05），但心肺最优点在不同场上位置的运动员间未出现显著差异（p=0.41）。心肺最优点与最大摄氧量（r=0.032，p=0.65）、通气阈值（r=-0.003，p=0.96）均未观察到显著相关性。研究结论：职业足球运动员在递增速度的亚最大运动过程中可便捷测得心肺最优点，且该指标不受运动员场上位置的影响。其与最大摄氧量、通气阈值无相关性，提示心肺最优点可为运动员机能评估提供独特且互补的信息。未来仍需开展相关研究以明确心肺最优点在运动员机能评估中的实际应用价值。（《国际心血管科学杂志》2018年；[在线先行出版]，页码0-0）