The objective of this study was to examine the validity and feasibility of four standardized aerobic fitness tests to either measure O2peak or to estimate O2max (e O2max) in patients with major depression disorder (MDD). To this end, all subjects (n=43) performed one maximal cardiopulmonary exercise test with gas exchange measurement (CPET) on a bicycle ergometer. Additionally, three submaximal tests (Åstrand-Rhyming bicycle ergometer test [ART], Physical work capacity test [PWC], and 6-min walk test [6MWT]) were performed within two weeks in counterbalanced order. e O2max from the submaximal tests was compared to the measured O2peak from CPET using rANOVAs, Bland-Altman plots, and correlation analyses. Feasibility outcomes (e.g., perceived exertion, discomfort, pretest anxiety, etc.) were compared via rANOVAs. On group level, e O2max estimated submaximally via ART and PWC did not differ from the CPET-based O2peak, whereas there was a bias in the 6MWT, as differences of the means increased in participants with higher O2peak. During CPET, only 56% achieved a primary or secondary criterion of maximum (physiological) exertion. On the group level, O2peak and e O2max determined with the different tests showed a sufficient degree of agreement (r≥.54, ICCs≥0.66, p<.001), but on the individual level, marked differences occurred between CPET-based O2peak and e O2max. Three of four CRF tests (CPET, ART, PWC) proved to be feasible and could be integrated into everyday therapy and monitoring of patients with MDD as an estimate for improvement of aerobic fitness. For the exact measurement of O2peak, CPET remains the gold standard, also in patients with MDD.
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