Reliability and Validity of the VmaxST Portable Metabolic Analyzer

Background: The reliability and validity of the SensorMedics VmaxST was tested. Methods: Thirty subjects (age = 24.5 ± 4.0 years, height = 174.8 ± 9.8 cm, weight = 70.3 ± 12.6 kg) performed treadmill exercise on three occasions, twice using the VmaxST and once using the SensorMedics 2900 system. Oxygen consumption (VO2; L/min) and heart rate (HR; beats/min) were measured continuously during three, 6minute stages: 80 m/min, 0% grade; 94 m/min, 5% grade; and 160 m/min, 0% grade, and VO2max. Results: Reliability was high, and measurement error was low for VO2 (Rxx range = 0.97 0.99, CI = 0.94 1.00, SEM = 0.03 0.08 L/min) and HR (Rxx = 0.94 0.99, CI = 0.88 1.00, SEM = 1.8 3.2 beats/min). Validity was high for VO2 (Rxy range = 0.92 0.98, CI = 0.84 0.99, SEE = 0.08 0.21 L/min) and HR (Rxy = 0.97 0.99, CI = 0.94 1.00, SEE = 0.9 1.8 beats/min). Mean differences in VO2 between VmaxST and 2900 were small yet significant (P < 0.001). Conclusions: The VmaxST demonstrated excellent reliability and validity for measuring VO2 and HR over several exercise intensities. Small overestimates in VO2 by the VmaxST are countered by low measurement error.