An Overview, Description and Synthesis of Methodological Issues in Studying Oxygen Consumption during Walking and Cycling Commuting using a Portable Metabolic System (Oxycon Mobile).

From the time of the independent discoveries of oxygen by Carl Wilhelm Scheele in Sweden and Joseph Priestly in England in the 1770s, there has been an ongoing chain of methodological developments, from the pioneering ones by Antoine Lavoisier until today, with the aim of measuring oxygen uptake and metabolic processes of man in motion (Mitchell and Saltin 2003). This historical development, has, not least during the last decades, also included both automated stationary and portable open-circuit metabolic measurement systems, which have been thoroughly reviewed recently (Macfarlane 2017; Ward 2018; Taylor et al. 2018). When two of the present authors (PS and HR) were trained as exercise physiologists, the golden standard method in this respect, the Douglas bag method (DBM), was the only, or the predominantly used method at our laboratory. In the 1990s, automated stationary open-circuit metabolic measurement systems started to be used, and HR evaluated some of them using DBM. He noted that it was not apparent that one could rely on the data produced in these “black box” systems. Still they have been used in many laboratories, and possibly there are a number of scientific articles based on them which might hold invalid data. One comment along that line was sent in 2001 as an e-mail from our teacher, professor emeritus Per-Olof Åstrand to an American colleague (Appendix 1). It ended with: “I have observed many odd data in the literature which can be explained as a consequence of uncritical use of modern, fancy electronic equipments without serious and competent evaluation of their accuracy”. For HR, these kind of experiences during the 1990s became an important impetus to develop a refined system for the Douglas bag method at the Laboratory for Applied Sport Sciences at the Swedish School for Sport and Health Sciences, GIH, in Stockholm, Sweden. That process was undertaken in close collaboration with Lennart Gullstrand at the Elite Sports Centre, The Swedish Sports Confederation, Bosön, Lidingö, Sweden. This text builds on that system, and many other developmental steps that have been taken since then. They have been applied to study a number of issues related to walking and cycle commuting, as part of the multidisciplinary research project on Physically Active Commuting in Greater Stockholm (PACS) at GIH. For its overall aims, see: www.gih.se/pacs One of the aims is to characterize the physiological demands of walking and cycle commuting in relation to absolute and relative demands of oxygen uptake (VO2). This is of interest in itself for understanding the nature of the physical activity during active commuting. Combined with other kinds of data one aim was also to better understand the potential health effects of active commuting. An important issue in this respect was to scrutinize whether the heart rate method for estimating VO2 (Berggren & Hohwü Christensen 1950) would be a reliable and valid method during cycle or walking commuting. To reach these goals we needed to use an automated mobile metabolic system. However, we had to work for a much longer time than expected due to a surprising number of diverse methodological challenges in measurements of both VO2 and heart rate (HR). They had to be considered and evaluated through a series of validity studies and checks. Some of the issues could be foreseen and were rather straight forward to handle, whereas others were unexpected, and the strategies to handle them had to be developed step by step as they appeared during the research process. Here this process will be first introduced, then described in more or less detail, and in cases of less details, we instead refer to issues in more depth in original articles. Finally, a synthesis of all studies and their consequences is elaborated on at the end of this appendix.Appendix in: Jane Salier Eriksson (2018). The heart rate method for estimating oxygen uptake in walking and cycle commuting: Evalutations based on reproducibility and validity studies of the heart rate method and a portable metabolic system. Doctoral thesis.FAA