The Effects of 100% Oxygen on Soccer Players

To the Editor.—  In the article entitled "Effects of 100% Oxygen on Performance of Professional Soccer Players,"1 the authors acknowledged the placebo effect of ergogenic aids on athletic performance. However, they did not control for a placebo effect in their study, that is, they compared the exercise performance of subjects after the subjects had breathed an unknown gas (either oxygen or air), but they did not measure exercise performance after the subjects breathed a gas known by them to be air. Hence, the subjects' exercise performance may have been influenced by their believing that the gas they had breathed during prior recovery was oxygen. This possibility is not negated by the information reported on subject preference, whereby four athletes retrospectively selected air as the preferred gas, four chose oxygen, and two thought both unknown gases were oxygen. Only two subjects had no preference.Because the placebo effect on performance was