 1. The intervention is a combination of possible benefits from oxygen and the disadvantage of canister weight. These cannot be separated. Placebo control is impossible because there is no means of providing placebo weight. Attempts to control solely for oxygen use without taking canister weight into account are clinically meaningless. In a recent COPD, chronic obstructive pulmonary disease study, cylinder weight was reported as a barrier to use by 93 of study participants. 