In‐Field Validity and Inter‐Unit Variability of Metabolic Carts During Simulated Exercise

, and 1.93%-4.24% for RER. No consistent relationship between system age and accuracy was observed, nor between annual maintenance and accuracy. The validity of metabolic carts for measuring respiratory gas variables varied significantly even between identical systems, despite passing manufacturers' calibration checks. Furthermore, inter-unit variability of most systems exceeded intra-unit test-retest variability, thus necessitating caution when using devices interchangeably, as this may increase measurement noise, even within the same laboratory. Most inaccuracies seemed related to technological errors, although some user errors were also identified, indicating the need for a holistic approach to identify errors.