I've heard it two ways:

1) Maintain no more than 85% of your max heart rate to burn fat. Greater than 85% will promote muscle wasting.

2) Go hard for 20 minutes and don't worry about your heart rate and you'll burn fat more effeciently WITHOUT muscle wasting. And you'll continue to burn fat for up to an hour after you get off the machine.

Thoughts ????

oh, that is just bad lol

Heart rate plays a very large role in what kind of endurance training you're going for. The higher intensities will isolate certain types of 'energy pathways' such as your lactate anerobic (glyocytissomethingorother) system which is hit more so when you work at around say 85% for a certain duration.

But you can go look that stuff up yourself, about the fat burning, you burn fat more efficiently (as opposted to lactate or glycogen - atp, pc, etc) when you work at lower intensities. This is why for an essential cardio workout it's easy to begin with a low intensity for 20-40 minutes. Around that 60% intensity you're burning more fat than muscle glycogen (actually i think your body hits reserves in the liver first, eh?). But as is commonely said, if you're more athletic to hit your THR zones higher up to the 85% area mainly because it gives conditioning to the other active systems that one must incorporate in their endurance training.

Another thing to note, go for at least 30 minutes, 30+ minutes is when your body really starts to condition your aerobic endurance (02, breathing, etc) so 20 minute is minimum, but over 30 is perfered. Especially in runners/walkers of any kind, a ten minute warm up and cool down is also good to add. So i always suggest a simple 20-30 min low intensity cardio workout for anyone trying to just burn fat and feel healthier, but if you're trying to condition yourself at all, 3 to 4 days at least of 50 min workouts, of course minimum. Eventually moving up to longer durations at lower intensities and working at higher intensities to build them up.

Another thing to note to anyone who does run, get a heart rate monitor for when you run, it's a great help to know your heart rate as you're working out, especially on longer runs.

But if you really want, you can find the Sport's Coach link through my links page on my website in my profile. I find the site great and gives lots of info on stuff like this, i read through the stuff often to keep it fresh in my mind and know i'm training right.

I understand that method is the conventional wisdom. But almost everything I've read recently about cardio says that low-intensity, long duration is "old technology." Pick up a Muscle Media or a Muscle and Fitness magazine sometime and see what they're saying about cardio now. Exercise physiologists with several more Ph.D.'s than me are reporting findings from extensive research that suggest high intensity, shorter duration will burn more fat without wasting muscle.

Believe me, I'm not a masochist that gets off to killing myself on a piece of cardio gear. I'd love to dail it back if it's more effective to do so. But I want to make sure I'm getting the bang for my buck. And there seems to be some conflicting information out there.

I just read yesterday, and don't remember where, that you want to be somewhere in between going all-out and a moderate pace and that you want to work out for at least 40 minutes for optimum fat-burning. I think I saw that bit of advice on the cool running website. Personally, I think you should use a variety of intensities.

That's a general rule and it does not take into consideration sparing muscle mass. That kind of advice is dished out to cardio-bunnies. Sprints and low intensity are probably the safest as far as sparing muscle and getting quality cardio. If you're not cutting, long, moderate intensity cardio sessions are fine, but if you are on a restricted calorie diet and trying to get lean and keep muscle, you have to be a little more careful.

There was something posted here ~ a week ago saying that some studies have been done that claim that consuming some whey protein before cardio (like in the AM, as opposed to doing it on an empty stomach) will still burn fat and help spare muscle since the protein doesn't have any effect on you blood sugar levels. Anyway, just something to consider.

and what names are behind this latest research? I'd like to look into this and see what's being discovered, but moreover, i'd like to see what has actually been proven and not just what seems to be good at this time. Science is something that develops over time so you can't take all new findings as sound proofs.

What about the fact that to metabolise fat it must be in the presense of oxygen. If someone is going over their aerobic threshold, obviously they're not going to be able to utilize fat as a fuel source well at all. This is why at higher intensities it conditions other energy 'pathways' to be more efficient. Endurance training is done at higher levels, fat burning at lower levels.

What is the new data that disproves this?

I'm not a personal trainer ... I'm not a doctor ... I'm not an exercise physiologist. I just read everything I can get my hands on about health and fitness. I'm not trying to disprove any theories or any science I'm just asking about something I've read and continue to see in what I feel are reputable magazines. All my fitness magazines are at work. I'll try to get around to finding some of the articles early next week and posting some of the information that's causing my confusion. Stay tuned. I appreciate your input.

Enter High Intensity Cardio in your search engine. The article below is typical of what you'll find. I'll post the research referred to in this article in the next post.

Twenty minutes of high intensity cardio increases your aerobic capacity (VO2max) dramatically, maintains lean muscle mass, boosts your metabolism during and after exercise, and burns more fat calories than 30-45 minutes of low intensity cardio. Sound too good to be true? It’s not. In one research study participants who engaged in 90 sessions of traditional cardio over a 20 week period lost 1% bodyfat, while participants who engaged in 25 sessions of moderate intensity cardio then 35 sessions of high intensity cardio over a 15 week period lost 3% bodyfat. Additional studies have shown that participants who engaged in short high intensity training lost 9 times more fat than those who performed long low intensity training. Longer low intensity cardio can actually be counterproductive for more fit individuals because it burns up hard earned muscle decreasing fat burning. It’s also incredibly boring and time consuming and doesn’t do much for your aerobic capacity.

I apologize for the length. The numbers in parenthesis refer to references at the end of the article (that I didn't include).

As exercise intensity increases, the proportion of fat utilized as an energy substrate decreases, while the proportion of carbohydrates utilized increases (5). The rate of fatty acid mobilization from adipose tissue also declines with increasing exercise intensity (5). This had led to the common recommendation that low- to moderate-intensity, long duration endurance exercise is the most beneficial for fat loss (15).

However, this belief does not take into consideration what happens during the post-exercise recovery period; total daily energy expenditure is more important for fat loss than the predominant fuel utilized during exercise (5). This is supported by research showing no significant difference in body fat loss between high-intensity and low-intensity submaximal, continuous exercise when total energy expenditure per exercise session is equated (2,7,9).

Research by Hickson et al (11) further supports the notion that the predominant fuel substrate used during exercise does not play a role in fat loss; rats engaged in a high-intensity sprint training protocol achieved significant reductions in body fat, despite the fact that sprint training relies almost completely on carbohydrates as a fuel source. Some research suggests that high-intensity exercise is more beneficial for fat loss than low- and moderate-intensity exercise (3,18,23,24).

Pacheco-Sanchez et al (18) found a more pronounced fat loss in rats that exercised at a high intensity as compared to rats that exercised at a low intensity, despite both groups performing an equivalent amount of work. Bryner et al (3) found a significant loss in body fat in a group that exercised at a high intensity of 80-90% of maximum heart rate, while no significant change in body fat was found in the lower intensity group which exercised at 60-70% of maximum heart rate; no significant difference in total work existed between groups.

An epidemiological study (24) found that individuals who regularly engaged in high-intensity exercise had lower skinfold thicknesses and waist-to-hip ratios (WHRs) than individuals who participated in exercise of lower intensities. After a covariance analysis was performed to remove the effect of total energy expenditure on skinfolds and WHRs, a significant difference remained between people who performed high-intensity exercise and people who performed lower-intensity exercise.

Tremblay et al (23) performed the most notable study which demonstrates that high-intensity exercise, specifically intermittent, supramaximal exercise, is the most optimal for fat loss. Subjects engaged in either an endurance training (ET) program for 20 weeks or a high-intensity intermittent-training (HIIT) program for 15 weeks. The mean estimated energy cost of the ET protocol was 120.4 MJ, while the mean estimated energy cost of the HIIT protocol was 57.9 MJ. The decrease in six subcutaneous skinfolds tended to be greater in the HIIT group than the ET group, despite the dramatically lower energy cost of training. When expressed on a per MJ basis, the HIIT group's reduction in skinfolds was nine times greater than the ET group.

A number of explanations exist for the greater amounts of fat loss achieved by HIIT. First, a large body of evidence shows that high-intensity protocols, notably intermittent protocols, result in significantly greater post-exercise energy expenditure and fat utilization than low- or moderate-intensity protocols (1,4,8,14,19,21,25).

Other research has found significantly elevated blood free-fatty-acid (FFA) concentrations or increased utilization of fat during recovery from resistance training (which is a form of HIIT) (16,17). Rasmussen et al (20) found higher exercise intensity resulted in greater acetyl-CoA carboxylase (ACC) inactivation, which would result in greater FFA oxidation after exercise since ACC is an inhibitor of FFA oxidation. Tremblay et al (23) found HIIT to significantly increase muscle 3-hydroxyacyl coenzyme A dehydrogenase activity (a marker of the activity of oxidation) over ET.

Finally, a number of studies have found high-intensity exercise to suppress appetite more than lower intensities (6,12,13,22) and reduce saturated fat intake (3). Overall, the evidence suggests that HIIT is the most efficient method for achieving fat loss. However, HIIT carries a greater risk of injury and is physically and psychologically demanding (10), making low- and moderate-intensity, continuous exercise the best choice for individuals that are unmotivated or contraindicated for high-intensity exercise.