## 7 Future Studies  
There is still a lack of information in the literature regarding the effects of interventions on the COP. However, some studies have shown associations between the COP and those cardiopulmonary variables that can be used to determine athletic performance [19]. Nevertheless, [PERSON] et al. [20] did not find the same association when evaluating 198 professional soccer players according to their different positions on the field, demonstrating that the COP is a distinct variable, although complementary to the analyzed variables (\(V\)'O\({}_{2}\)max and anaerobic threshold). Similarly, more recently, [PERSON] et al. [27] found no association between the COP and \(V^{\prime}\)O\({}_{2}\)max or ventilatory threshold in adolescent male and female volleyball players, corroborating the findings of [PERSON] et al. (2019). Additionally, there is still a lack of studies addressing the influence of the type of ergometer used, type of exercise, type of protocol, body position (prone, supine, reclined, sitting, or standing), diet (high in carbohydrates versus high fat), menstrual cycle, and medications on the COP, and/or the influence of ergogenic resources, and mechanistic and physiological studies. Finally, a clear advantage of the COP is that it does not require elevated levels of exertion during CPET, making it beneficial for individuals who are exercise intolerant or unable to perform the test. As a result, the COP serves as a valuable and applicable index, particularly for groups that require specialized expertise. In this regard, it is important to consider that individuals with panic disorder may experience compromised results during CPET because of phobic anxiety, which can consequently affect their breathing capacity ([PERSON] et al., 2018; [PERSON] et al., 2019; [PERSON] et al., 2019). [PERSON] et al. (2019) sought to test the hypothesis that exercise-related respiratory symptoms in patients with panic disorder are not abnormalities in cardiorespiratory interactions. To this end, the authors compared the COPs of patients with panic disorder with those of healthy individuals matched by sex and age. The results showed no significant difference in the COP between the patients with panic disorder and healthy individuals (21.9 \(\pm\) 0.47 versus 23.4 \(\pm\) 0.65 and \(p\) = 0.067). [PERSON] et al. (2019) tested 442 individuals with HF and reduced ejection fraction to evaluate and compare the prognostic power of several parameters during submaximal CPET for risk stratification and found that the COP had the greatest prognostic power among all analyzed parameters, even being superior to \(V^{\prime}\)O\({}_{2}\)max. Furthermore, a COP value \(\geq 36\) achieved 100% sensitivity and 89% specificity for predicting death and heart transplantation outcomes. Another interesting point was that the COP maintained its high predictive power regardless of sex, age, disease etiology (ischemic or non-ischemic), baseline heart rate (sinus rhythm or atrial fibrillation), and the presence of chronic kidney disease. In older adults, [PERSON] et al. (2019) found that after 18 months of detraining due to the limitations inherent to the SARS-CoV-2 pandemic, octogenarian older adults demonstrated changes in different submaximal parameters obtained from CPET when compared to the cutoff values existing in the literature, including the COP; 32% of the evaluated cases had values greater than 30, indicating a worse prognosis, according to a previously published study (2019). In summary, few studies have evaluated the COP in vulnerable populations, and there is an emerging need for new studies in special populations, particularly given that the COP is an index with prognostic potential. Recently, [PERSON] et al. (2019) demonstrated that the COP is a robust and promising tool for risk stratification in patients with HF. Through detailed analyses, the COP exhibited high sensitivity (100%) and specificity (89%) in predicting critical outcomes, such as death and heart transplantation, in patients with HF and reduced ejection fraction.