Each subject performed 2 exercise tests. They were requested to abstain from food, coffee, and cigarettes for at least 3 h prior to testing. The first test was performed to familiarize subjects with the testing procedure and gas exchange apparatus, and to determine maximal oxgyen uptake. This test consisted of a modified Balke Ware protocol with the speed individualized from 2.5 to 4.5 mph depending on the subject s height and fitness. Tests were continued to volitional fatigue/dyspnea, and the Borg 6 to 20 scale was used to quantify subjective level of exertion each minute.
The second test, performed approximately 1 week later, was designed as follows. All subjects walked for 1 min at a workload of 2.0 mph/0% grade. Based on the initial test, an individualized peak treadmill speed was chosen for each subject. The ramp rate (rate of continuous change in speed and grade) was calculated using the following: (1) the baseline maximal oxygen uptake; (2) the predetermined peak treadmill walking speed; and (3) a projected test duration of 10 min for each subject. A computer program was written in Basic language to facilitate these calculations for each subject.