Exercise prescription: principles and current limitations.

Exercise prescriptions must be both safe and effective, while maximizing patient compliance. Safety can be threatened by physical injury, cardiac emergencies and environmental hazards. Risk can be reduced by individualizing the prescription, although the stress ECG contributes little to the prevention of the exercise catastrophe. Effectiveness of a prescription must be gauged by development of aerobic power and muscular strength, reduction of obesity, improvement of flexibility and control of coronary risk factors. The variability of patient response limits the potential for accurate laboratory prescription of exercise; fine tuning must depend upon the patient's immediate reactions.