During each 30-min exercise period, minute ventilation was measured at 10 and 20 min using a section of corrugated tubing placed between the valve on the facemask and a
Fleisch pneumotachograph (General Medical Corp., West Sacramento, CA); flow signals recorded from the pneumotachograph were amplified (Validyne Engineering Corp., Northridge, CA) to yield volume signals and then recorded on a visicorder (Honeywell 1858; Honeywell Test Instruments Division, Denver, CO).