Assessment of exercise capacity typically is performed on a motorized treadmill or a stationary cycle ergometer. In the United States, however, treadmill exercise is generally the preferred modality.
Furthermore, untrained subjects will usually terminate cycle exercise because of quadriceps fatigue at a V˙ O2 that is on average 10% to 20% below their treadmill peak V˙ O2.13
Cycle ergometry also requires subject cooperation in maintaining pedal speed at the desired level, usually 60 rpm, although modern ergometers that are electronically braked maintain a steady work rate at variable speeds.
Several studies have demonstrated a consistent relationship between exercise capacity determined with a treadmill and a cycle ergometer, although the latter mode of exercise tends to produce a lower peak V˙ O2.14,15
Cycle ergometry may be preferred in subjects with gait or balance instability, severe obesity, or orthopedic limitations or when simultaneous cardiac imaging is planned.