A common strategy for people trying to lose weight is to focus on calories, so they make calorie burning the biggest aim of all their workouts, with the added goal of being in the "fat burning zone". See our new page on The 7 Steps to New Year's Weight Loss. People often do very long and repetitive cardio sessions — walking or jogging for an hour or more at a relatively low, even level of intensity. But this isn't necessarily the most efficient way to burn off unwanted fat, and it's certainly not the most effective way to achieve and maintain a strong, lean body over time.

To do that, you need to boost your metabolism, which regulates your body's ability to become (and stay) lean. And shifting your metabolism depends on improving your fitness and supporting your goal with good nutrition, which is 70% of your ability to get the results you want.

When your body turns food and oxygen into energy — something it does throughout the day, virtually all day — it burns calories. That process takes place in your cells' mitochondria, which need oxygen to burn those calories efficiently. So the more oxygen your body is capable of processing per minute (a function of your VO2 max — more on that in a moment), the more calories it can grind through on a given day.

In other words, being fit helps your body run more like a finely tuned machine — one that's naturally inclined to eliminate excess weight.

"People who have a higher level of fitness burn more calories even while at rest and asleep," Hyman says. Exact numbers are difficult to nail down because each person's resting metabolic rate is unique (based on muscle mass, age, genetics and even climate). Still, some experts estimate that fit, muscular adults can burn an extra hundred calories or more per day — while at rest.

It's important to note that in the course of their daily activities and workouts, fit adults can and do burn a couple thousand more calories daily than unfit, more sedentary ones.

And here's the beauty of it: Fit people are naturally more inclined toward activity and tend to exert themselves at higher levels. That's because exercise and activities of all kinds become easier as your fitness improves, and even intense levels of exertion become more comfortable. All of which makes calorie-burning activities a much more appealing proposition, thus further increasing active inclinations.

This is what's known as a "benevolent circle" (as opposed to a vicious one) — and the more fit you become, the more you can take advantage of its fat-burning effects.

Copyright (c) 2008 Charles Carter