Figure 2: Schema of the submaximal-intensity exercise experiment (SEE) setup. Note: (A, B) The experimental gas (H2 gas or artificial air as the control gas) was supplied using a gas cylinder (A) and buffered in a 200-L Douglas bag (B). (C) Subjects inhaled the gas through a one-way valve and a respiratory mask. (D) Exhaled breath was sampled at a rate of 150 mL/min and respiratory parameters were detected by a metabolic gas analyzer. (E, F) Exhaled gas was collected using a 50-L Douglas bag (E) to measure breath acetone concentration, which was measured by gas chromatography (F).