I posted this before somewhere on the board, but it warrants posting again ...

It's long, but full of good info:

The arguement in favor of fasted early morning cardio goes something like this:

(1) WHEN YOU WAKE UP in the morning after an 8-to-12 hour overnight fast, your body's stores of gylcogen are somewhat depleted. Doing cardio in that state causes your body to mobilize more fat because of the unavailability of glycogen.

(2) EATING CAUSES A RELEASE of insulin, which interferes with the mobilization of bodyfat. Less insulin is present in the morning; therefore you burn more bodyfat when you do your cardio in the morning.

(3) THERE'S LESS CARBOHYDRATE (glucose) in your bloodstream after an overnight fast. With less glucose available, you'll burn more fat.

(4) IF YOU EAT IMMEDIATELY before a workout, you have to burn off carbs you just ate before tapping into stored bodyfat.

(5) WHEN YOU DO CARDIO IN THE MORNING, your metabolism stays elevated for a period of time after the workout is over. If you do cardio in the evening, you will benefit from it, but you fail to take advantage of teh afterburn effect because your metobolic rate drops dramatically as soon as you go to sleep.

Research supports this theory. A study performed at Kansas State University and published in Medicine and Science in Sports and Exercise showed the subjects burned a kilogram (2.2 lbs.) of fat sooner when the exercised in a fasted state in the morining than when the did it later in the day.

The researchers measured respitory gas exchange, caloric expenditure, and carbohydrate/fatty acid metabolism and found that the amount of fat burned during aerobic exercise amounted to 67% of the total energy expenditure in the morning after a 12 hour fast. That's substantially higher than the 50% expenditure achieved when the subjects did the same exercise later in the day or after eating.

A similar study published in the Journal of Applied Physiology looked at the effects of aerobic exercise on lipid oxidation in fed vs. fasted states. The researchers conculded, "Our results support the hypothesis that endurance training enhances lipid oxidation in men after a 12-hour overnight fast."

Yet another paper, "Optimizing Exercise for Fat Loss," reports, "The ability of exercise to selectively promote fat oxidation should be optimized if exercise is done during morning fasted metabolism."

When it comes to "real world fat loss", few people have more experience than Chris Aceto (nutrition guru/advsior to many pro bodybuilders).

Aceto is a firm believer in morning cardio. He unequivocally states, "The fastest way to tap into stored bodyfat is to do cardio first thing in the morning on an empty stomach."

Aceto believes that looking at calories only in terms of energy in vs. energy out is "limited thinking." He asserts that there are more factors involved in real-world results than just energy balance. It all comes back to the old arguement, are all calories created equal?

"Absolutely not!" Aceto declares. "A calorie in not just a calorie, and exercise physiologists freak out when they hear that."

"These guys are working from the assumption that it's just a matter of calories in vs. calories out, period," Chris continues. "With that line of reasoning, they'd be forced to say that if I consumed nothing but candy bars and Coca-Cola and took in 100 calories less than maintenance, I'd lose weight. We know it's not that simple. You have to account for ratios of carbs, protein, and fat."

"Then there's meal frequency: From real-world results we know you put on more muscle mass from five or six meals a day than from three meals a day. There are more things involved than just calories."

There are many other reasons you might want to consider making morning cardio a part of your daily routine. Landry, despite his doubts about whether the fuel source matters admits, "If I had to pick a single factor I thought was most important in a succesful weight-loss program, it would have to be exercise first thing in the morning."

Here are some of the additional benefits of doing cardio early in the morning:

- It makes you feel great all day by releasing mood-enhancing endorphins.

- It energizes you and wakes you up.

- It may help regulate your appetite for the rest of the day

- Your body's circadian rhythm adjusts to your morning routine, making it easier to wake up at the same time every day

- You'll be less likely to blow off your workout when it's out of the way early.

- You can always make time for exercise by setting your alarm earlier in the morning.

- It increases your metabolic rate for hours after the session is over.

Of all those benefits, the post exercise increase in your metabolic rate is the one most talked about. Scientists call this afterburn effect "excess postexercise oxygen consumption," or EPOC.

Looking only at the number and type of calories burned during the session doesn't give you the full picture. You also need to look at the number of calories your elevated metabolism continues to burn after the workout is over.

That's right -- work out in the morning, and you burn calories all day long.

You burn somewhere between 10 and 30 calories extra after exercise at an intensity of less than 60 to 65 percent of maximal heart rate (MHR). In other words, a casual stroll on the treadmill will do next to nothing to increase your metabolism.

EPOC does increase with the intensity (and duration) of the exercise, however. According to Willmore and Costill in Physiology of Sport and Exercise, the EPOC after moderate exercise (75 to 80 percent of MHR) will amount to apporximately .25 calories per minute, or 15 calories per hour. That would provide an additional expenditure of 75 calories. An extra 75 calories is definately no earth shattering, but it does add up over time. In a year, it would mean (in theory) that you'd burn an extra 5.2 pounds of fat from the additional calories expended after your workouts.

One way to get a significant post-exercise afterburn is high-intensity interval training (HIIT). You alternate brief periods of high intensity work (85% of maximum heart rate or more) with brief periods of lower-intensity work. Studies on the effects of HIIT have demonstrated a much higher EPOC, which can add substantially to the day's calorie expenditure.

In one study scientists from the University of Alabama compared the effects of two exercise protocalls on 24 hour energy expenditure:

- Group #1 cycled for 60 minutes at a moderate intensity.

- Group #2 performed HIIT, cycling for 2 minutes at high intensity followed by 2 minutes at low-intensity.

The group that performed HIIT (group #2) burned 160 more calories in 24 hours than the low intensity group.

That would translate to an extra 11.8 pounds of fat burned in one year if they did HIIT five days per week instead of conventional low-intensity training.

Ironically, weight training has a much higher magnitude of EPOC than aerobic training.

Studies have shown increases in metabolic rate of as much as 4-7% over a 24-hour period from resistance training.

Yes - that means bodybuilding does burn fat – albeit through an indirect mechanism. For someone with an expenditure of 2500 calories per day, that could add up to 100 - 175 extra calories burned after your weight training workout is over.

The lesson is simple: Anyone interested in losing body fat who is not lifting weights should first take up a regimen of bodybuilding, then – and only then – start thinking about the morning cardio!

A common concern about doing cardio in the fasted state, especially if it’s done with high intensity, is the possibility of losing muscle. After an overnight fast, glycogen, blood glucose and insulin are all low. As we’ve already concluded, this is an optimum environment for burning fat.

Unfortunately, it may also be an optimum environment for burning muscle because carbohydrate fuel sources are low and levels of the catabolic stress hormone cortisol are high. It sounds like morning cardio might be a double-edged sword, but there are ways to avert muscle loss.

All aerobic exercise will have some effect on building muscle, but as long as you don’t overdo it, you shouldn’t worry about losing muscle. It's a fact that muscle proteins are broken down and used for energy during aerobic exercise. But you are constantly breaking down and rebuilding muscle tissue anyway. This process is called "protein turnover" and it’s a daily fact of life. Your goal is to tip the scales slightly in favor of increasing the anabolic side and reducing the catabolic side just enough so you stay anabolic and you gain or at least maintain muscle.

How do you build up more muscle than you break down? First, avoid excessive cardio. Aceto suggests limiting your cardio on an empty stomach to 30 minutes, and then it would be "highly unlikely that amino acids will be burned as fuel." He also mentions that "a strong cup of coffee should facilitate a shifting to burn more fat and less glycogen. If you can spare glycogen, you’ll ultimately spare protein too." You might also want to consider experimenting with the thermogenic ephedrine-caffeine-aspirin stack (or it’s herbal equivalent).

Second, give your body the proper nutritional support. Losing muscle probably has more to do with inadequate nutrition than with excessive aerobics. Provide yourself with the proper nutritional support for the rest of the day, including adequate meal frequency, protein, carbohydrates and total calories, and it’s not as likely that there will be a net loss of muscle tissue over each 24-hour period.

Third, keep training with heavy weights, even during a fat loss phase. Using light weights and higher reps thinking that it will help you get more "cut" is a mistake: What put the muscle on in the first place is likely to help you keep it there.

Still petrified of losing your hard-earned muscle, but you’d like to take advantage of the fat-burning and metabolism-boosting effects of morning cardio?

One strategy many bodybuilders use is to drink a protein shake or eat a protein only meal 30-60 minutes prior to the morning session. The protein without the carbs will minimize the insulin response and allow you to mobilize fat while providing amino acids to prevent muscle breakdown.

In conclusion, it seems that morning cardio has enough indisputable benefits to motivate most people to set their alarms early. But let’s talk bottom line results here:

Does it really result in more "real world fat loss" than aerobics performed at other times of the day or after eating? I have to believe it does. Experience, common sense and research all tell me so.

Nevertheless, this will obviously continue to be an area of much debate, and clearly, more research is needed. In the meantime, while the scientists are busy in their labs measuring respiratory exchange ratios, caloric expenditures and rates of substrate utilization, I’m going to keep waking up at 6:00 AM every morning to get on my elliptical.

References

1. Aceto, Chris. Everything you need to know about fat loss. Club Creavalle, Inc. (1997).

2. Bahr, R. Excess post-exercise oxygen consumption – Magnitude, Mechanisms and Practical Implications. Acta Physiol Scand. Suppl. (1992) 605. 1-70.

3. Bergman, BC, Brooks, GA. Respiratory gas-exchange ratios during graded exercise in fed and fasted trained and untrained men. Journal of Applied Physiology. (1999) 86: 2.

4. Brehm, B.A., and Gutin, B. Recovery energy expenditure for steady state exercise in runners and non-exercisers. Medicine and Science in Sports and Exercise. (1986) 18: 205,

5. Brybner, BW. The effects of exercise intensity on body composition, weight loss, and dietary composition in women. Journal of American College of Nutrition, (1997) 16: 68-73

6. Landry, Greg. The Metabolism System for Weight Loss. Greg Landry. (2000).

7. Maehlum, S., etc al. Magnitude and duration of post exercise oxygen consumption in healthy young subjects. Metabolism (1986) 35 (5): 425-429.

8. McCarty, MF. Optimizing Exercise for Fat Loss. Medical Hypothesis. (1995) 44: 325-330