In brief:It is accepted that circuit weight-training programs are effective for developing and maintaining muscular strength, but it is less clear that these programs are aerobic and will develop and maintain cardiorespiratory fitness. The authors evaluated the Nautilus Express Circuit (NEC) in terms of the American College of Sports Medicine recommendations for developing and maintaining cardiorespiratory fitness. They studied energy cost (oxygen uptake) and heart rate responses in ten men and eight women during the 20-minute weight-training program. Although heart rate responses were maintained within recommended ranges, VO2responses were not. The authors concluded that the NEC elicited only minimal aerobic exercise intensity.