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There are big promises out there; exercise gurus come from every angle to peddle their latest metabolizing workout plans. One common promise is that your metabolism will churn at an increased rate long after you perform their xyz workout. They might even claim that this will free you to eat whatever you want, whenever you want it.

It's time to set the record straight. There is such a thing as exercise after-burn. This means that, after performing exercise, your body burns additional calories above and beyond its resting state until that resting rate is stabilized. This period of time can range from 15 minutes to 48 hours. The process is called excess post-exercise oxygen consumption or EPOC. During this after-burn period, the body increases its oxygen intake to replace oxygen stores necessary to power certain energy systems in the body. Muscular energy known as ATP-PC is spent during exercise; this ATP must be replaced. To do this, an increased level of oxygen consumption is required. Increased oxygen also helps remove lactate buildup in the muscles, increases ventilation, improves blood circulation, and restores body's temperature to pre-exercise levels. In short, exercise takes the body from its normal, resting state, to a state of energy debt. EPOC returns the body back to its efficient, resting state.

How metabolic after-burn can help you

The duration of EPOC is linked directly to the intensity of exercise. High-intensity cardiovascular exercise has been clinically proven to have the greatest impact on after-workout oxygen consumption. Multiple studies show a 5% increase in metabolism that can last for minutes or days based on the intensity of that exercise. Scientists use a criterion called VO2 max, whsich measures the maximum oxygen uptake, or the maximum cardiovascular ability of a human. VO2 max is reached when a human exerts enough effort in duration and intensity to reach a stable level of oxygen uptake even with an increased level of exercise intensity.

Bahr and Sejersted in 1991, conducted a study in which subjects exerted different levels of oxygen uptake while engaging in 80 minutes of cardiovascular activity, 29%, 50%, and 75% of VO2 max to be exact. The subject that ran at 75% of VO2 experienced a 5% gain in his metabolism for 10.5 hours after exercise. The subject that ran at only 29% of VO2 max only experienced 20 minutes of metabolic after burn. This translated to 150 extra calories burned after exercise for the subject that ran at 75% of VO2 max and a mere 5 extra calories burned for the subject that ran at 29%. Some studies have even shown up to a 48-hour increase in calorie burn after exercise if the exercise is sufficient in duration and intensity.

This translates to a significant boost in metabolism, but only if you engage in high-intensity.

cardiovascular exercise for a significant duration of time. An extra 150-calorie burn in 10 hours doesn't allow you to pound down a hamburger combo meal and feel good about it, but it is like running one mile at about a 10-minute mile pace.

The conclusion

When those exercise gurus promise big boosts in your metabolism by using their magic workouts, don't run out for a box of ding dongs. Though you will gain a boost in your metabolism -- and don't get me wrong, any boost is a good boost -- you can easily lose the benefits from that boost by over-eating. In short, work out hard, work out long, and keep that metabolism churning.

- Craig, Nybo