Mid Sweden University

Purpose: It is essential to validate portable metabolic systems, not only in laboratory settings, but also in field measuring conditions, such as prolonged moderate exercise at low temperatures, high humidity and with external wind.

Methods: VO₂, VCO₂, RER and V_E were measured using the Oxycon Mobile (OM), with a windshield, during cycle ergometer exercise: (I) indoors at three submaximal workloads with no wind or with external wind (13–20 m·s^-1) from front, side and back; (II) at two submaximal workloads outdoors (12 ± 2^oC; 86 ± 7% RH), with and without a system for drying the ambient air around the air sampling tube; and (III) at one workload outdoors for 45 min (5 ± 4^oC; 69 ± 16.5% RH). Any physiological drift was checked for with pre- and postmeasurements by the Douglas bag method (DBM).

Results: A minor effect of external wind from behind was noted in RER and V_E (-2 and -3%)._. The system for drying the ambient air around the gas sampling tube had no effect on the measured levels. A small difference in VCO₂ drift between the OM and DBM (1.5 mL·min^-2) was noted in the stability test.

Conclusion: Heavy external wind applied from different directions generally does not affect the measurements of the OM. Furthermore, when using a unit for drying the ambient air around the gas sampling tube, the OM can accurately measure VO₂, RER and V_E   at submaximal workloads for at least45 min under challenging conditions with regard to humidity and temperature.