A better burn

Getting a clinical fitness test can help improve your sports performance -- and help you shed unwanted pounds. That's why I signed up for a VO2 max test and fitness assessment at the Institute for Exercise Medicine & Prevention (I.EM.PHIT), formerly part of Children's Hospital in St. Paul.

The VO2 max test -- which measures oxygen consumption, expiration rates, heart rates and daily caloric burn rates -- tells you the exact heart rate at which your body switches from burning fat as a fuel source to burning carbohydrates. This tricky little number, called your anaerobic threshold, can change how you exercise because knowing what it is -- and how to broaden it -- can help increase the percentage of fat you burn during workouts.

I.EM.PHIT, the University of St. Thomas, the University of Minnesota and some fitness facilities offer the test, which costs between $75 and $120.

According to the website ProMedical Healthcare, VO2 Max testing gives you "your ideal heart rate training zone," which allows you to create training programs that are more efficient, results-oriented and help you "burn fat more efficiently."

Luke Carlson, an exercise physiologist at Discover Strength in Plymouth, said that track athletes, coaches and kinesiology professors at the universities of Minnesota, Iowa and Wisconsin regularly use VO2 max tests to boost performance.

Even if you're not an athlete, knowing your anaerobic threshold -- and the other numbers the VO2 max test reveals -- can help you lose weight because it tells you how many calories your body burns each day when resting or active and when you burn fat. That way you can plan your caloric intake and exercise accordingly.

Taking the test

Off the bike, Coffey used calipers to measure my fat body mass, and had me grab the daylights out of a grip tester. Then his assistant Kevin measured my flexibility in inches as I reached for my shoes and again as I leaped for the stars in a vertical jump. I came back to the clinic the next day to get my results.

I consider myself fairly fit, but it turns out I have work to do. The test showed I burn 1,238 calories a day when sitting still and that when I exercise vigorously daily, that number jumps to 2,353 calories. My grip, reach and leg strength proved excellent. My vertical jump and oxygen uptake were "good." But the test showed my anaerobic threshold was low. And that's not so good, because the higher your anaerobic threshold, the more fat calories your body burns.

When my heart rate is at or below a lowly 113, I burn fat. When it's above 113, I burn carbs. During aerobics or spinning classes, I burn a lot of calories, but it turns out they are rarely fat calories. Rats.

Most folks who bike, jog or do some other aerobic activity get their heart rates pretty high and burn carbs. But some athletes my age also can burn fat when their heart rates are as high as 142 beats per minute. That's what I'd like to be able to do. Then, I could burn up my fat stores faster and more efficiently than if I just burned carbohydrates.

Coffey suggested I focus on interval training and plyometric (or jumping) exercises to keep my heart rate above 134 beats per minute (bpm) during each hour of cardio exercise. He suggested I take my heart rate through intervals to beef up endurance. Get the heart rate clipping at 134 bpm for two minutes, he said, then elevate it to, say, 160 bpm for two minutes and then bring it down again for two minutes and then back up. After three to six months of interval training, Coffey said, our bodies often reset and adopt an expanded fat-burning zone.

Athlete or not, nearly everyone can burn fat better with the help of training and a watch-like heart-rate monitor, Coffey said. What you need to do is estimate your targeted heart rate, which is the rate at which you'll need to train to burn calories more efficiently.

You can get a rough estimate of your maximum heart rate by doing this math: Subtract your age from 220, then multiply that by 80 percent to get the upper range of your target heart rate. To get the lower range, subtract your age from 220 and multiply by 65 or 70 percent.

Because I'd taken a VO2 max test, I knew that my actual maximum heart rate was 178 bpm. My next step was to try a workout in which my heart rate never fell below 134 bpm (75 percent of my maximum heart rate). I recruited a couple of friends to join me in an hour of interval training on a treadmill. We closely monitored our heart rates and varied them every two to three minutes.

At the end of 50 minutes, the heart rate monitor I wore said I'd burned roughly 560 calories, 25 percent of which were fat. That's pretty darn good. So good, in fact, that I'm going to keep doing interval workouts.

Staying at a constant heart rate, like so many of us do in aerobic classes or lunchtime jogs, isn't going to turbocharge a workout. My take-home message: Mix it up -- slow, fast, slow, fast.