Reliability Of A Wearable Metabolic System During High-intensity Treadmill Testing

Wearable metabolic systems are lightweight, portable devices that allow for exercise testing using a dynamic mixing chamber or breath-by-breath analysis, in a laboratory or field setting. Because even the smallest change in outcomes can have significant implications for clinical populations and athletes alike, establishing the reliability of wearable metabolic systems is critical. PURPOSE: The purpose of the current study was to determine the test-retest reliability of a wearable metabolic system breath-by-breath analyzer during high intensity treadmill testing. METHODS: This trial of healthy, eligible adults aged 18-29 years compared metabolic outcomes in 2 maximal cardiopulmonary exercise tests (CPET) on a treadmill using the Bruce protocol. Primary outcomes included measurements of oxygen consumption (VO2), and carbon dioxide production (VCO2) and secondary outcomes included Respiratory Exchange Ratio (RER), Minute Ventilation (VE), Tidal Volume (VT), Respiratory Frequency (RF), fraction of oxygen in expired air (FeO2), and fraction of carbon dioxide in expired air (FeCO2). Measures were recorded during the final 2 minutes of each 3-minute stage. Both CPETs were performed at the same time of day, 2 to 21 days apart depending on participant availability. A within-subjects analysis was performed for test-retest reliability. RESULTS: 24 participants (15 males) with a mean (SD) age of 25.4 (2.8) years completed both CPETs and were included in the analysis. Intra-class correlation coefficient (ICC) was used for test-retest reliability. Excellent reliability (ICC = 0.98-0.97) was observed across all stages for VO2, VCO2, VE, VT, RF. RER did not show good reliability (ICC = 0. 0.40-0.31) in the early stages but did reach moderate reliability (ICC = 0.69) by stage 3. FeO2 showed moderate reliability (ICC = 0.50-0.55) in the early stages and increased to near excellent reliability (ICC = 0.84-0.87) by stage 4 and FeCO2 showed moderate reliability in the early stages (ICC = 0.74-0.77) and increased to excellent reliability (ICC = 0.9) as participants neared peak exertion. CONCLUSIONS: This wearable metabolic system is a reliable measure of direct expired gas exchange variables at submaximal and maximal intensities during treadmill testing in healthy young adult men and women.