Test-retest reliability of a portable gas analysis system under free living conditions.

Introduction: K4b2 (COSMED Srl Italy) is a portable device that is considered valid and reliable for measuring oxygen uptake (VO2) and carbon dioxide production (VCO2) under laboratory conditions. Objectives: Evaluate the test-retest reliability of K4b2 during walking, stair climbing and descending stairs under free living conditions. Methods: Twelve participants completed two self-selected comfortable paced walking tests and 20 participants completed two self-selected comfortable paced stair climbing and descending tests. VO2 and VCO2 were measured during the tests using K4b2. Results: ICCs for VO2 (ICC & 95% CI: 0.91, 0.72-0.97) and VCO2 (0.91, 0.72-0.97) of walking demonstrated high reliability whereas reliability was moderate for stair climbing (VO2: 0.82, 0.6-0.93; VCO2: 0.73, 0.44- 0.88) and low for descending stairs (VO2: 0.67, 0.33-0.85; VCO2: 0.51, 0.1-0.77). Conclusion: K4b2 is a highly reliable device for VO2 and VCO2 measurement during self-paced walking in free living environment.