Open circuit spirometry

Peak aerobic power was measured at baseline using an individualized treadmill protocol with open-circuit spirometry (ParvoMedics; Sandy, UT). Subjects warmed up to determine the level walking speed that elicited a heart rate of ~70% of age-predicted maximal heart rate. During the test, this speed was maintained and treadmill grade was increased by 2% every 2 minutes. Heart rate was monitored continuously using a 12-lead electrocardiogram (Quinton Q4500; Quinton Instruments, Seattle, WA) and blood pressure was measured during each exercise stage. VO₂ peak was the average of the two highest consecutive 30-second VO₂ measurements.

Maximal aerobic power was measured at baseline and 4 months in the WL group only, to facilitate exercise prescriptions, using an individualized treadmill protocol with open-circuit spirometry (ParvoMedics, Sandy, Utah). Subjects warmed up to determine the walking speed that elicited a heart rate of approximately 70% of age-predicted maximum. During the test, this speed was maintained and treadmill elevation was increased by 2% every 2 minutes. Heart rate was monitored continuously using a 12-lead electrocardiogram (Quinton Q4500; Quinton Instruments, Seattle, WA) and blood pressure was measured during each exercise stage. VO_2max was confirmed by one of the following criteria: 1) heart rate within 10 beats per minute of age predicted maximum, 2) respiratory quotient ≥1.1, or 3) plateau in VO₂.