Validity and reliability of the K5 wearable metabolic system during high-intensity treadmill testing in healthy, young adults

Background The COSMED K5 portable metabolic system (K5) enables field-based assessments of gas exchange variables. This study evaluated the validity and test-retest reliability of K5 relative to the laboratory-based ParvoMedics TrueOne2400® system (PM) during treadmill cardiopulmonary exercise testing (CPET) in healthy young adults.Methods Thirty-one adults (mean age 25.8 ± 2.8 years, 61.3% male) completed three Bruce protocol CPET trials: one using PM and two using K5. The order of the first two trials was randomized and counter balanced; the third used K5. Breath-by-breath data were averaged over the final 90 seconds of each CPET stage. Validity was assessed using paired comparisons and Bland-Altman analyses. Reliability was evaluated using intraclass correlation coefficients (ICC).Results The K5 demonstrated excellent test-retest reliability for oxygen consumption (VO2) and carbon dioxide production (VCO2) (ICC = 0.90–0.98). Relative to PM, K5 values for VO2 and VCO2 were slightly higher at lower intensities and lower near peak intensities (P < 0.01). Bland-Altman analyses revealed proportional bias for VO2 and VCO2 across workloads.Conclusions The K5 is a valid and reliable device for treadmill CPET in healthy young adults. Small systematic differences exist relative to PM at extreme workloads yet remain within acceptable clinical limits, supporting its utility for longitudinal and applied assessments requiring portability.