​The Moxus Modular Metabolic System Evaluated with Two Sensors for Ventilation Against the Douglas Bag Method

The ability to assess the true oxygen uptake in humans has been a continuing aspect of research for centuries. Beginning with the classic Douglas bag method, this method sets out to measure oxygen consumption and energy expenditure with high validity and reliability. Currently, other automated methods have been employed to more accurately assess these measures. The discussed device, the moxus metabolic system is an automated metabolic system, utilizing a mixing chamber and precise gas analysis.

To investigate the differences between the Douglas bag method and the Moxus metabolic system, each ventilation sensor was tested twice on different days, to understand reliability measures. These measures, such as the coefficient of variation and typical error were calculated and used in comparison to the Douglas bag method, along with data pertaining to each device’s validity. The researchers selected thirteen well-trained endurance athletes, who were all accustomed to cycling as a work mode.

The participants performed one pre-test to decrease the learning effect and then four tests for data collection. The trials were performed on a Monark pendulum ergometer cycle. The graded exercise began with 9 minutes at 50 W and VO2maxmeasurements at a cadence of 90rpm and 2 minutes of exercise at 180 W. The VO2max was calculated through averaging the largest consecutive values across 60 seconds at maximal exercise. As for the Douglas bag method, it was calculated through intervals of 30 seconds and 10-second intervals for the Moxus metabolic system. Also blood samples were collected to assess to ensure there was minimal lactate accumulation and then again 3 minutes after trials to assess average blood lactate accumulation.

When comparing reliability amongst the methods, there were no reported differences between test-retests in any of the variables at varying powers. For validity, VO2max had presented an increasing deviation between the two methods and seemed to have been related to the size of the measured values. As for resting VO2 no statistical differences were reported with either form of evaluation. In addition there were no significant difference in respiratory exchange ration between the Moxusand Douglas methods of assessment. Some possible limitations that could have imposed an effect on the results were found from biological variations between participant’s physical fitness and ability to perform the trials. In addition, laboratory conditions such as humidity when assessing inspiration and expiration could have some effect on the measurements.

As demonstrated through the trial and analysis, only small variations were found at VO2max but none at all other powers. Further research about the specific validity and reliability of differing methods within a laboratory setting are still needed to ensure the true measurements of these devices.