Want to burn more fat? Here's how to schedule your cardio for research-driven results.

You've finally found a cardio routine that works for you. It pushes you (but not too hard), fits into your busy schedule and, best of all, it has helped you maintain a lean, shapely figure. But there's still that one little question that, if cleared up, might take your training to the next level. It's the ever-present quandary that has yielded so many contradictory answers from personal trainers and fitness experts alike: When exactly is the best time to do cardio? We've done the legwork to find the research on the topic, and here we offer the pros and cons of doing cardio at various times during your workout week. The answers to your (fat) burning questions are right under your nose.

6:30 AM
First Thing in the Morning
Come on, what's wrong with getting up an extra 45 minutes early and knocking that cardio out of the way for the day? You get it done before you even have time to fully wake up and realize what you're doing. Many people swear that doing cardio first thing in the morning -- especially before breakfast -- is the best way to burn fat and get the day started right.

Pros
"Doing cardio on an empty stomach can result in burning more fat," confirms Michele Olson, PhD, professor of exercise physiology at Auburn University in Montgomery, Alabama. "The body is engineered to spare its carbs, so when exercising on an empty tank, the body will use more fat for fuel in an effort to save as much stored carbs as possible."

But wait, there's more: During the night, the body slips into a fat-burning cycle to preserve glycogen for the brain. Studies show that you can take advantage of this by doing cardio first thing in the morning before eating and promote the usage of fat for fuel by working muscles.

Cons
So if it were really that simple, how come everybody doesn't do cardio this way? "Research shows that the amount of extra fat burned is not an appreciable amount," notes Olson. "Furthermore, there's no significant increase in total caloric expenditure whether you exercise on an empty stomach or after a meal," she says, citing a study published in the International Journal of Sports Medicine (1998). Additionally, you risk dipping into muscle protein for fuel, which is counterproductive to keeping your metabolism high.

Bottom Line
"Weight control is based on total calories burned, and during cardio the body uses a combination of carbs and fat as fuel," Olson points out. In other words, while doing cardio right after waking up is effective, doing it later in the day will give you virtually identical results. Besides, why risk losing muscle when all you have to do is eat a little something before your workout? Your best bet is to take an amino acid supplement or ingest whey protein without added carbs. A research study confirms that when amino acids are taken before cardio, more fat is used as fuel. So you'll be able to train harder and burn more calories and fat overall.

30-Minute Intermediate Interval
1. Warm-up: 5 minutes
2. Moderate intensity: 30 seconds
3. Low intensity: 60 seconds
4. Sprint: 30 seconds
5. Low intensity: 60 seconds
6. Complete steps 2-5 six more times
7. Cool-down: 4 minutes

Carbs During Cardio You did your cardio, burned that fat, and now can't control your appetite. What gives? Try sipping Gatorade on the treadmill or stair-stepper. Ingesting a carbohydrate drink (like Gatorade) during a cardio session helps prevent overeating following exercise, reports the International Journal of Sport Nutrition and Exercise Metabolism. Study participants who ingested the carb drink ate significantly fewer calories throughout the remainder of the day. --Michele Olson, PhD

7:00 PM
Before or After Lifting?
Unless you have kids, you probably don't like to wake up any earlier than absolutely necessary. If rising with the sun to do early morning cardio sounds about as appealing as watching reruns of the Anna Nicole Show, you may opt to do it before your weight training at the gym. Good idea or bad? "It depends on how much, how long and how intense," states Olson. And, of course, it depends on your goals. Let's break it down.

Before:
If you're training for an endurance event -- a half-marathon, triathlon, etc. -- you'd do right to put cardio before any other workout. That way, you pour the most energy and effort into the session to produce optimal performance results.

Or you might want to do cardio before your weight workout for the warm-up effect. "If the cardio workout is light, it can serve to warm up the muscles, which in turn encourages you to move right into high-intensity lifting without having to do as many warm-up sets," Olson explains.

After:
On the flip side, if shaping the body of your dreams is your main objective, you may want to save cardio for after your weight workout. "An intense cardio workout will take away from an effective weight-training workout," Olson says. "Cardio burns both fat and carbs, and those carbs won't be available for weight training if you do cardio first. That's a problem since they're the key source of energy for weight training; you may not be able to lift at a beneficial intensity."

You can also burn more fat by increasing your lean mass, which eats up calories all day long. So for building a little muscle, weight training should take priority in your workout. This way, your energy level will be high and your intensity won't suffer during the part of your program that matters most to you. You may not be able to work at the same intensity if you do cardio after weights -- especially on leg day -- but you might tap into fat stores more quickly.

Bottom Line
Put cardio first if endurance performance is your main focus. Otherwise, "You'll burn more fat and total calories by doing cardio after weight training," Olson remarks. "But following a high-rep, light-weight, circuit-type program with cardio will burn more total calories from both carbs and fat."

35-Minute Steady-State Cardio
1. Warm-up: 5 minutes
2. Steady-state ride: 25 minutes
3. Cool-down: 5 minutes

Best type of cardio No matter how you prefer to sweat, interval training is your best bet. Michele Olson, PhD, explains that interval training is the most effective method of aerobic exercise when it comes to fat-burning and cardiovascular conditioning. "This is an efficient way to do cardio since interval cardio somewhat mimics weight training (an effort followed by rest between sets)," says Olson. "Research shows that more fat and total calories are burned with this approach. And since interval cardio is more intense than steady-state cardio, you'll continue to burn more fat and calories following the workout." A typical interval session includes 20-30 minutes of alternating sprinting for 30-60 seconds with walking or jogging for 30-60 seconds. You can do this on any piece of cardio equipment or outside on a track or pavement.

1:00 PM
On Non-Weight-Training Days
Doing cardio and weight training on separate days is the most effective scenario, states Olson. If you want to get the most out of your cardio without undermining your weight workout or vice versa, the only logical way to do it is on days that you don't lift.

Pros
"The amount of stress on the body from doing a high volume of exercise [such as when you do weights and cardio in the same workout] may detract from gains in fat-burning and metabolic-boosting muscle mass," Olson explains. High-intensity, long-duration workouts may cause your body to break down muscle protein for energy, according to a study published in the International Journal of Sports Nutrition and Exercise Metabolism (2001). This is why splitting up cardio and weight training is so effective.

Cons
This is a good choice for those who want to maintain or build muscle and decrease bodyfat, yet it may mean you're training every day. That could present some problems if you have limited time, high demands at work, home or school or all of the above. Also, training every day or almost every day may compromise your body's recovery ability, reducing your ability to build fat-burning muscle tissue and affecting your immune system.

Bottom Line
Doing cardio on non-weight-training days is the best approach according to studies, which show that total caloric expenditure is increased when each respective workout is done on separate days. More days training equals more calories burned, equaling less fat on your frame. Just be sure you have at least one complete day off from training each week.

40-Minute Advanced Interval
1. Warm-up: 4 minutes
2. Run: 2 minutes
3. Sprint: 1 minute
4. Jog: 30 seconds
5. Complete steps 2-4 nine more times
6. Cool-down: 3 minutes

Michelle Basta Boubion is a personal trainer and recreational athlete who enjoys marathons, triathlons and ice cream, but not necessarily in that order.
By Michelle Basta Boubion, NSCA-CPT
Photos by Michael Darter