Before starting a vigorous exercise program, check with your doctor for guidance on how to pace yourself. Your doctor may recommend an office visit, including an electrocardiogram (EKG) and fasting blood tests for total and high-density lipoprotein (HDL) cholesterol, triglycerides and blood sugar. If you have multiple risk factors for heart problems, some physicians recommend that you have an exercise stress test, in which you walk on a treadmill for about 10 minutes. As you walk, the speed and incline of the treadmill are gradually increased, in order to raise your heartbeat. The exercise stress test may indicate a potential heart problem that would alter your approach to exercise.
Although not yet part of a standard medical evaluation, exercise specialists use a treadmill test to measure your VO2-max -- that's how much oxygen your body uses at maximum effort. This measure is often expressed as your MET level, which stands for metabolic equivalent.
One MET is how much energy you use at rest, two METs are twice the resting expenditure, etc. Sedentary individuals may only reach six to eight METs, depending on their age, whereas young endurance athletes may exceed 20 to 25 METs. This figure correlates closely with your aerobic fitness level. Researchers are actively studying if VO2 max measurements should be performed on a more regular basis.