How vigorously are you able to work out? The answer may predict how long you will live.

In a recent study, people who had the ability to reach a certain level of exercise intensity when they worked out tended to live longer than the people in their age group who couldn't reach that intensity level. Boost your exercise capacity -- and your longevity -- with interval training by adding short bursts of more intense activity to your workout.

Not everyone's health allows for intense physical activity, so before engaging in interval training, consult your healthcare provider if you have a medical condition, physical limitations, or are exercising for the first time. An example of interval training would be jogging for a few minutes here and there during a long walk. Or, you could temporarily increase the resistance level on your exercise bike for a few minutes once or twice during your workout. Interval training may eventually increase your exercise capacity, which is a measurement of how vigorously you're able to work out expressed in metabolic equivalents (METs). One MET is roughly equal to the amount of energy -- in the form of oxygen -- the body uses when sitting or at rest. The higher the MET value during an activity, the more oxygen the body requires to perform that activity. Activities with an MET value of 3 include walking a dog, yoga, and golf. To expend 6 or more METs try jogging, swimming laps, or bicycling more than 10 mph. If you're able to work out and reach at least 85 percent of the MET value predicted for your age group, you're in good shape. If not, incorporate changes slowly into your workout routine to improve your exercise capacity.