Abstract: A method for prescribing an exercise regimen for a particular subject to either maximize cardiovascular performance or to lose weight involves the use of a microprocessor-based cardiopulmonary exercise system to measure oxygen uptake and carbon dioxide production on a breath-by-breath basis. These measured quantities are used to calculate energy expenditure and a subject's respiratory exchange ratio from which a fat metabolization curve can be plotted. By examining the length of a plateau in the curve where the fat substrate utilization is maximized, and noting the average heart rate in this zone, a target heart rate for optimal weight loss is arrived at. If the goal of the exercise is cardiovascular improvement, the anaerobic threshold can readily be determined as the midpoint between maximal fat utilization and the maximum acceleration towards the point where the respiratory exchange ratio becomes equal to 1 or the fat metabolism goes to 0.