Having been an athlete for most of my life, I figured I knew my way around the gym. On a typical day, I'd hit the treadmill or elliptical machine for 30 minutes, then move to the weight machines. And that's what I started to do when I recently joined a gym. Then I got my assessment -- you know, the review of your habits a lot of gyms do. And the review told me I was doing something wrong.

Hit the weights hard, the assessment said. Then go to cardio.

What?

"The body needs to burn through its sugar source first before it taps into the fat," says Iman Nikzad, who runs the fitness program at my LA Fitness near Irvine, Ca. "You burn the sugar while doing the weights then burn the fat while doing the cardio."

I did some more research and, turns out, he's right and I was wrong. The optimal workout is a 10-minute warm-up on a low-impact cardio machine followed by 30 minutes of weights and then 30 minutes of intense cardio.

Yes, really.

"Efficiency is the key when structuring any workout, so long-duration cardio should not be done in the beginning of the session," says certified strength and conditioning specialist Jim Smith. "The most intensive training should be done first in the workout, when you are at your best."

By starting with weights, you alert your muscles to trigger the proteins that churn through calories while you train. So even though you're probably spent after 30 minutes of weights, your body is ready to eat fat faster than it would if you started by "telling" the body to attack sugar.

A lot of people get this wrong, thinking weight training diminishes the effect of the cardio work. It's the opposite. Just remember the phrase: "Muscle eats the fat." If you want to lose the flab -- and who doesn't? -- you want your muscles as active as possible. That means starting with weights.

And if you only have 30 minutes total, go for weights instead of cardio. That sounds counterintuitive, since we feel sweating is "proof" we're losing fat. But you will lose a lot more fat by pushing and pulling weights and then going on a brisk walk in your neighborhood (or even at the mall). The guy or gal who is dripping buckets on the Stairmaster is getting a good workout, but you're likely getting a better one by getting sore and not getting soaked.

Nick Bromberg contributed to this story.