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Purpose The portable metabolic analyzer COSMED K5 (Rome, Italy) allows for switching between breath-by-breath (BBB) and dynamic micro-mixing chamber (DMC) modes. This study aimed to evaluate the reliability and validity of the K5 in BBB and DMC at low, moderate, and high metabolic rates. Methods Two K5 simultaneously operated in BBB or DMC, whereas (i) a metabolic simulator (MS) produced four different metabolic rates (repeated eight times), and (ii) 12 endurance-trained participants performed bike exercise at 30%, 40%, 50%, and 85% of their individual power output at V˙O2max (repeated three times). K5 data were compared with predicted simulated values and consecutive Douglas bag measurements. Results Reliability did not differ significantly between BBB and DMC, whereas the typical error and intraclass correlation coefficients for oxygen uptake (V˙O2), carbon dioxide output (V˙CO2), and minute ventilation (V˙E) ranged from 0.27% to 6.18% and from 0.32 to 1.00 within four metabolic rates, respectively. Validity indicated by mean differences ranged between 0.61% and -2.05% for V˙O2, 2.99% to -11.04% for V˙CO2, and 0.93% to -6.76% for V˙E compared with MS and Douglas bag at low to moderate metabolic rates and was generally similar for MS and bike exercise. At high rates, mean differences for V˙O2 amounted to -4.63% to -7.27% in BBB and -0.38% to -3.81% in DMC, indicating a significantly larger difference of BBB at the highest metabolic rate. Conclusion The K5 demonstrated accurate to acceptable reliability in BBB and DMC at all metabolic rates. Validity was accurate at low and moderate metabolic rates. At high metabolic rates, BBB underestimated V˙O2, whereas DMC showed superior validity. To test endurance athletes at high workloads, the DMC mode is recommended.

A simplified V-slope method was used to visually determine the first point of departure from linearity of carbon dioxide output (VCO2) plotted against oxygen uptake (VO2). The point at which VCO2 departed from a line with a slope equal to 1.00 was visually selected as the gas exchange threshold during incremental exercise. The simplified method of threshold detection was compared with a computerized V-slope method. Both methods were used to determine the gas exchange threshold during incremental cycling (10 W.min-1) in 17 untrained female subjects. The thresholds occurred at 41.1% and 45.1% of VO2max using the computerized and simplified V-slope methods, respectively. The correlation between the oxygen uptake measured at the threshold using the two methods was 0.95. Power output, VO2, and heart rate values determined at the gas exchange threshold using the simplified V-slope method were significantly higher than the corresponding values obtained using the computerized V-slope method. The simplified V-slope method consistently placed the gas exchange threshold at the work rate that was about 10 W above the power output determined by the computerized method. Although the two methods were highly correlated, the simplified V-slope method tended to overestimate threshold values determined from a computerized gas exchange method.

The purpose of these experiments was to determine the effects of oral caffeine ingestion on the kinetics of oxygen uptake (VO2), expired carbon dioxide output (VCO2), and expired ventilation (VE) in the transition from rest to exercise. Nine male subjects underwent three repetitions of constant load cycle ergometer exercise (approximately 80% ventilatory threshold) on two occasions. A single blind experimental procedure was followed, with one trial being performed 60 min after the subject ingested caffeine (7 mg X kg-1), while the second trial required the subject to ingest a placebo with the treatment order being counterbalanced. Ventilation and gas exchange were monitored by open circuit techniques. The data from three repetitions of the same protocol were pooled and modeled with a single-component exponential function incorporating a time delay: (formula; see text) Kinetic analysis of VO2 revealed no significant difference (P greater than 0.05) in the mean response time between treatments. In contrast, the mean response time for VCO2 and VE were longer (P less than 0.05) for the caffeine trial when compared to the control experiment. These data suggest that caffeine will influence both VCO2 and VE kinetics in the transition from rest to work and should be considered by investigators when planning experiments to study ventilatory and gas exchange kinetics during exercise.