Beyond the madness: a balanced approach to standardization, practicality and innovation in exercise physiology threshold assessment

With great interest, we read the reply by Chavez-Guevara et al. (2024a) regarding the initial discussion, 'Stop the madness! An urgent call to standardize the assessment of exercise physiology thresholds' (Chavez-Guevara et al., 2024b). We are pleased to find consensus on several of our key points (Sperlich & Gronwald, 2024), particularly the recognition of system-dynamic complexity and the interconnections between physiological subsystems, which are crucial for validating paradigms linking physiological thresholds. Nevertheless, we feel the need to clarify three specific points discussed in their response as they are relevant for both the scientific and practical community: We agree with Chavez-Guevara et al. (2024a) that some standardized approaches, such as those proposed by Merrell et al. (2024), already exist and should be implemented where applicable. While these frameworks for standardizing test conditions and prerequisites are indeed valuable, they fall short in addressing critical domains, such as the determination of exercise physiological thresholds. This limitation extends to the development of global databases for maximal and submaximal physiological metrics. Further standardization in areas such as the use of blood lactate concentrations or oxygen uptake for decision making requires more than the simple adoption of test condition checklists. While the creation of checklists for threshold determination, analysis, and reporting can enhance consistency and assist those who may be overwhelmed by the diversity of assessments, these measures alone are insufficient to capture the inherent complexity and variability of physiological responses during exercise. Chavez-Guevara et al. (2024a) suggest that relying solely on technological advancements (e.g., computational models or wearable technologies) is insufficient to fully comprehend the complexity of physiological thresholds, and we agree with this. However, our position is not an argument for a purely 'technoscientific' approach but rather a blend of technological innovation and system-dynamic physiological insight. We do not reject classical methods like lactate threshold or gas exchange analysis. Instead, we propose that emerging approaches, such as those based on heart rate variability or muscle oxygen saturation, can complement traditional techniques. Assessing objective markers of internal load to analyse the complex dose-response relationships during exercise requires valid, reliable procedures and precise measurement principles that can be further developed through technological innovation. Such advancements have the potential to contribute to a more holistic understanding of organismic responses, serving as proxy measures of exercise 'dose' alongside traditional objective markers of internal load (e.g., oxygen consumption, heart rate, blood lactate concentration), external load (e.g., power, speed), and subjective markers of internal load (e.g., rating of perceived exertion). An additional critical consideration is the day-to-day variability in physiological responses, arising from both technical and biological variations, which poses significant challenges for research as well as practical applications. For example, fluctuations in physiological markers such as oxygen uptake and blood lactate levels can result in misleading conclusions when solely relying on standardized testing methods (Zinner et al., 2023). Complementary technologies, such as wearable devices, enable continuous monitoring (Duking et al., 2022) and could assist in detecting and accounting for these daily fluctuations – provided these devices are valid and reliable. This real-time monitoring offers a valuable means to assess and mitigate the impact of day-to-day variability, thereby improving the accuracy of physiological assessments. Chavez-Guevara et al. (2024a) also raise concerns regarding technological innovations such as AI and computational models. While we acknowledge these concerns, we advocate for the continued development and refinement of these technologies, as long as they are employed with methodological rigour. Wearable technologies, AI models, and other computational approaches hold considerable promise for improving the transferability between laboratory and field settings, as well as for enabling real-time data collection. This is particularly valuable when compared to relying solely on exercise and training prescriptions derived from CPET protocols, which may fail to account for varying field conditions in the days or weeks following testing. However, the successful application of these technologies requires interdisciplinary collaboration to ensure their validity and reliability. In their counterpoint, Chavez-Guevara et al. (2024a) emphasize the importance of accuracy over practicality in exercise physiology threshold assessments, particularly in clinical or athletic settings. While we agree that accuracy is critical, we contend that, in some cases, a high level of precision may not be necessary for effective decision-making. For instance, when classifying individuals as 'fit' versus 'unfit' for basic health assessments or fitness programmes, precise physiological thresholds may be less essential. This may also apply to health and preventative sports, where approximate training zones could suffice, given that most recreational athletes lack access to precise training controls. In such scenarios, general markers or rough estimations can provide adequate guidance for practical decision-making without requiring the highest levels of accuracy. Furthermore, when working with patients in clinical settings, where compliance and safety are paramount, practicality may outweigh the need for absolute precision. High-performance athletes and clinical patients often require different diagnostic approaches, and practical limitations should not be viewed as obstacles but as considerations for test adaptation, ensuring effective decision-making without undue burden (e.g., fatigue or unnecessary test exhaustion). This balance remains critical for both ethical reasons and ensuring adherence to interventions. In sum, while we are aligned on many key points, we maintain that technological innovations, combined with methodologically robust, practical, and adaptable testing protocols, hold the potential to advance a more comprehensive and individualized understanding of exercise physiology thresholds. As researchers and practitioners, we see our role as facilitating both the progression and application of these innovations, ensuring that future standards accurately capture the complexity of the field while remaining practical and adaptable to diverse populations and areas of application. 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. No competing interests declared. All authors have approved the final version of the manuscript and agree to be accountable for all aspects of the work. 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