Madness or progress? The dilemma of standardizing exercise physiology thresholds

With great interest, we read the opinion article by Chavez-Guevara et al. (2024) in The Journal of Physiology advocating for the standardization of methods in assessing exercise physiology thresholds to enhance precision, accuracy and reproducibility, as well as to resolve existing inconsistencies in the field. Although the intent to standardize methods is commendable, we wish to highlight several reasons why a protocol 'madness' has occurred and argue that solving this 'madness' may be impractical, if not impossible. Tailored protocols ensure relevant data collection for the distinct nature and interplay of various cardiovascular, haemodynamic, pulmonary and metabolic features, accommodating the needs of patients with chronic diseases, as well as the general and athletic population of different ages. Thus, cardiopulmonary exercise test (CPET) protocols must vary widely in exercise modality (e.g. cycling, running), intensity progression (step or ramp increment, inclination), step length and measurement techniques (e.g. gas exchange, blood lactate) to account for the typical interindividual characteristics of each population and setting. This diversity extends to the statistical methods for data analysis, such as linear and polynomial regressions, expert ratings, consensus finding and advanced computational models such as machine learning algorithms. This variation in CPET protocols is crucial to address specific research objectives, population characteristics (e.g. age, sex, fitness level), exercise modalities, measurement techniques, statistical approaches and study goals. We acknowledge that inconsistencies have arisen because of the replacement of validated test protocols with standardized ramp characteristics, step lengths and increments. Additionally, replacing validated physiological reference point calculations with those derived from entirely different test protocols, which have varying ramp characteristics, step durations and intensity increments, has contributed to these inconsistencies. We support the authors' proposal to standardize the application of already validated test protocols in specific populations and to avoid the indiscriminate interchange of calculations and test protocols. The practical implications of testing protocols for decision-making regarding the intensity, duration and frequency of subsequent training sessions are crucial. Invasive or exhaustive testing can lead to fatigue or extended recovery periods, affecting an athlete's training process. In this case, a balance between diagnostic depth and practical limitations is necessary. Additionally, different application fields, such as clinical settings vs. high-performance sports, have varying demands for diagnostic precision and resources. Non-invasive and cost-effective methods are prioritized in clinical settings to enhance patient compliance and manage healthcare costs. Conversely, high-performance sports justify more detailed assessments despite higher financial costs and invasiveness. The need to cater to specific needs within different contexts further complicates the quest for universal standards. Moreover, the reductionist approach of simplifying protocols to create universally practical methods, such as those intended to compare results between studies, often fails to capture the complex nature of physiological subsystems. This includes novel, promising internal load indicators with the potential for exercise physiology threshold determination. It is crucial to balance simplification for standardization with the need for detailed, specific insights provided by more complex protocols and models. This balance is essential to accurately evaluate system-dynamic regulatory processes and the acute responses of the organism during exercise. Investigations and validation studies of the relationships between blood lactate, ventilatory, cardiovascular and metabolic thresholds should consider the involvement of different physiological subsystems. The inter-relations among these subsystems and applied testing protocols could lead to deviations in agreement (Jamnick et al., 2020), thus shifting the understanding from physiological 'thresholds' to physiological 'transitions'. Consequently, the question arises whether there can be an 'absolute' gold standard approach. This would necessitate defining approved limits of agreement based on the population and field of application, such as clinical settings, recreational sports or high-performance sports. Therefore, it is imperative to appreciate the system-dynamic complexity and interconnections of physiological subsystems, as well as to critically evaluate whether a simplified approach can truly serve as a universal standard. Practitioners often develop a deep understanding of the acute training response and chronic adaptation specific to their preferred assessment protocols and evaluated populations. Introducing new standardized protocols could disrupt these established practices, undermining years of experiential knowledge and data history of tested individuals. Thus, although standardization may benefit from a theoretical perspective, practical application often requires modified protocols tailored to specific athletes or patient groups. The experiential 'bench to bedside' knowledge held by practitioners is a critical asset that should be leveraged rather than diminished by standardization efforts. As Chavez-Guevara et al. (2024) mention, '… why should we then insist on coming up with novel methods?' A common goal is to reduce invasiveness and enhance usability and compliance. This involves introducing novel methods and measurement principles based on technological innovations implemented, for example, in wearable applications, depending on the field of application and the evaluated population. In the field of exercise and training prescription, it is essential to consider further development to create long-overdue concepts for defining training volume (e.g. duration, distance) in addition to intensity demarcation (Tschakert et al., 2022). This reflection extends to understanding why prescriptions from CPET protocols for prolonged exercise can lead to highly heterogeneous physiological responses depending on exercise duration. Day-to-day fluctuations in physiological measures (Zinner et al., 2023) and personal as well as external influences (e.g. environment) (Gronwald et al., 2020) in connection with established CPET protocols reveal significant limitations of physiological threshold determinations in the laboratory when transferring to field conditions for days and weeks post testing as a result of altered dose–response relationships. We agree that organizing regular meetings for experts to share best practices is valuable for the community. However, reaching a consensus among experts is doubtful because of the need to adjust established workflows and the difficulty in comparing previous findings. Although standardization in exercise physiology testing is commendable, a single test protocol cannot capture the complex nature of physiological responses. Modifiable, problem-specific approaches that incorporate new methodologies and technologies are essential. Additionally, practitioners' experiential knowledge should be considered to maintain established training dose–response relationships. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. The authors declare that they have no competing interests. B.S. and T.G. conceived or designed the work, drafted the work or revised it critically for important intellectual content, and approved the final version of the manuscript submitted for publication. Both authors agree to be accountable for all aspects of the work. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed. No funding was received.