Who needs a bag?

In this issue of Medicine & Science in Sports & Exercise sub((R)), Hopker et al. ( super(4)) report on the reliability of gross efficiency as measured using the Douglas bag technique ( super(3)) (often miscited), finding a total within-subject variation of 1.5%. This excellent reliability is considerably better than previously reported results in which breath-by-breath systems were used (e.g., Moseley and Jeukendrup [ super(6)] and Noordhof et al. [ super(7)]). The article of Hopker et al. ( super(4)) focuses largely on a meticulous investigation of the Douglas bag technique itself, particularly sampling reliability, residual volume of the Douglas bag, gas exchange between the Douglas bag and ambient air, and measurement of the gas volume. To be sure, they could have been even more complete by detailing exact methods of gas analyzer calibration via zero and span gases plus a midrange gas standard. Nevertheless, to their credit, they have previously reported on the equally important issue of accuracy and reliability of power measurement during cycling ( super(5)).