## 8 Perspectives and Limitations  
This literature review focuses on the COP as an emerging prognostic marker that has garnered increasing attention in diverse populations. Recent research suggests that the COP may serve as a greater indicator of mortality risk than conventional measures, such as \(V^{\prime}\)O\({}_{2}\)max and maximum heart rate, because this marker considers cardiovascular and pulmonary capacity and the interplay between these systems.  
With advances in technology, novel tools and devices may be developed to measure and monitor the COP more accurately and efficiently, facilitating a deeper understanding of how the COP is related to mortality in different populations. Furthermore, investigating this marker could enhance our understanding of the underlying mechanisms linking cardiorespiratory fitness and health, thereby aiding in the identification of strategies for preventing and treating chronic diseases associated with physical inactivity and sedentary lifestyles.  
So far, it is worth noting that the COP does not have a scientifically robust basis; there is a lack of mechanistic studies that demonstrate the potential and originality of the COP as an independent index, despite some existing work illustrating some possible prognostic value, especially in clinically impaired individuals. For instance, individuals with cardiorespiratory complications commonly present high basal levels of ventilation at rest, which, in turn, predisposes these individuals to a high probability of demonstrating an elevated COP. In addition, it is unclear what additional clinical and prognostic information is gained by examining the COP metric because elevations in \(V^{\prime}\)E-\(V^{\prime}\)CO\({}_{2}\) at the VT1 point and \(V^{\prime}\)E-\(V^{\prime}\)CO\({}_{2}\) slope would provide obvious prognostic information that is sought when ordering a CPET. In this way, this substantial oversight is concerning because a large number of studies published by the [PERSON] and [PERSON] group clearly detail the significance of gas exchange and ventilatory response during the part of the exercise that is being proposed in these more modern studies, such as the COP. Another point that requires attention concerns the heterogeneity of the studies reviewed, especially in terms of the subtypes of HF, sex, age group, type of ergometer used, and level of physical conditioning. Additionally, it is worth noting that the COP has poor performance in multivariate models, some of the reasons being the complexity of the data and the interaction between multiple variables, as demonstrated by a study that used different adjustment models for conventional risk factors and found important reductions in COP prediction after multivariate analyses [23; 24]. For example, collinearity can lead to instability problems in the model coefficients and make it difficult to identify the real impact of the COP on predictions or relationships between variables. Furthermore, in some cases, the COP alone may not be sufficient to represent all aspects of cardiorespiratory health or disease severity. Subgroup analyses can provide a more detailed and accurate view, adjusting the interpretation of the COP according to the specific characteristics of the patients.  
Finally, additional studies are required to gain a deeper understanding of the potential of the COP as an independent marker in both healthy and cardiovascular patient populations.