Why Cardio Burns Muscle?

Hi All,

I just had a quick question and was hoping to get some feed back.  I was talking to my friend about exercise and how it is commonly agreed that by doing cardio you loose more weight but a higher percentage of that weight is muscle.  He seemed to be under the impression that doing cardio burns  the current calories you have from eating then goes to burning fat, and I really didn't have a good, scientific reason on why cardio burns more muscle.  So I was hoping that someone could explain what actually happens in the body that causes it to burn muscle while doing a lot of cardio.  Any input, suggestions, ideas would be much appreciated.

Thanks All!

I happen to agree with your friend but my opinion is based on personal observation and not science.  I know there are posters here that will give the scientific explaination but I tend to believe that most people that are eating a healthy diet, doing regular cardio, and losing weight are losing mostly if not entirely fat.

"oh oh pick me i know the answer - waving my hand in the air"

spoke to the doctor about this the other day as ive been excerising hard 7 days a week for 2+months and lost absolutley nothing, nor did my body tone up or shrink.

the doctor said that due to working out very hard 90min spinning sessions my body was stressed. My body didnt know i wanted it to burn fat, it just thought i was over working and therefore tried to protect itself. It burnt muscle instead of fat as muscle uses a lot more calories to live than fat does. my body actually slowed my metaoblism and stored all the fat possible as it assumed that i was being overworked and underfeed so it went into stravtion mode.

so basically if you do cardio for too long eg over an hour or push your body to hard it will burn muscle to save your vital fat stores (arent our bodies annoyling efficient). The best way to burn fat is to work your body out at around 60-70%, which means wearing a heart monitor at the gym and not pushing yourself till you cant breath.

i hope this was helpful though im sure some of the real fittness buffs on here will point you to the helpful sites. in fact Mellor loves this question, que Mellor, im sure he'll be on here later

"Burning muscle" makes me cringe.  Your body can cannabilize muscle tissue for fuel in case of exttreme dietary deficiencies -- i.e., you are starving.  I think what is actually being discussed here is burning fuels stored in your muscles.  Those fuels are necessarily replaced during recovery.  But, if you keep your cardio workouts moderate, a significant amount of your calories should be coming from stored fat.  However, my HRM almost never gets above 50% for fat useage, which means that if I burn 1000 calories during a workout, 500 or less come from fat and that translates to less than 50 grams of fat or something less than 2 ounces.

Running doesnt burn muscle. It burns fat. Sorry I was in the military and ran a lot and was fit and toned and still able to do weights and everything. There was no muscle being burnt on my hour and a half two hour runs.  if that was the case I wouldnt have been able to carry my 100 pound ruck for 20 miles or buddy carries or a million other little things.

Absolutely, anyone can burn muscle. It is a phenomenom of not enough protein. Long distance runners do not look like wrestlers or weight lifters in most cases. Why? They burn so many calories that their intake of protein and in some cases total calories is deficient.
Once the body feels its under attack it will hold fat and burn muscle. We release a catabolic enzyme after working out hard for a period of 3 weeks. The body begins to look for extra protein. It can be avoided by the intake of 1 gram of protein per pound of weight per day. Whey protein supplements can help prevent muscle burn.
Lastly, I am cutting fat and saving muscle by adding protein. I still watch the protions of food servings but make sure I hold 2000 calories per day. Most lifteres use a 50% carb 35% protein and 15% good fat. Some do 60% carb 30%protein and 20% fat. At the end of the day these boys keep their muscle on. Cheers
M

This is a good topic, one I almost started myself.  I'm reluctant to use weights even though I understand the benefits of muscle on metabolism.  I'd rather have that scrawny runner look than look like I have any muscle.  I wonder if running six days a week and skipping weights would actually work best.

A lot of non-professional distance runners look like wrestlers or weight lifters because they are wrestlers and weight lifters.  Professional distance runners tend to be leaner because it was their lean slow twitch natural build that got them into the sport in the first place.

That doesn't help my case.  I'm basically trying to change my whole build through running. 

Thanks for all the Replies! I knew this is a pretty hot topic here on the forums, and I am sure each body is different on how it burns and how efficient it is, but its good to know as much about something as possible, so keep the theories coming! Thanks again for all your inputs.

I guess the way I see it is that if (from the previous example) you burn 1000 calories and only 500 of them are fat calories.... that leads one to wonder where the other 500 come from. I am in no way disagreeing that cardio is good for you, because i believe it is. But the way i picture it is if you are loosing weight, and you do cardio only that burns 1000 calories a day then you will burn 7000 in a week. Say 50% of that is fat, so the other 50% is coming from muscle, which is 3500 calories. Now if you are lifting only you dont burn as many calories, so say you burn 500 calories a day from lifting, but 80% of those calories are fat. So it takes 2 weeks to burn the 7000 calories, but only 1400 of them are muscle loss. Overall they have burned the same amount of calories, even though it took the person lifting twice as long, but the person lifting in my eyes burns more actual fat.  The person just doing cardio definitely looses more weight, and definitely looses more fat in the same amount of time, but also looses more muscle as well.

That is just the way I picture it in my mind I guess. Perhaps this is a wrong perception of how your body uses its fuels and what not, and please feel free to tell me differently. I guess another key point to this is that i am assuming the body is ina weight loss mode, i.e. in a calorie deficit and trying to loose weight. I would probably agree that if you are eating to maintain or even over maintanance this would not have as much of an impact on muscles. As others have said it comes from the nutritional deficit your body sees.  Also, please dont think I am saying to not do cardio, I think cardio is great and necessary, Im just trying to understand better how the body works and how it uses its fuels and what not.  

Thanks again for all the inputs, as i said this is just the way i picture things, and if people see them differently, or have other theories I would love to hear them. Thanks again for all the inputs! I love learning about this stuff.

 

(edited to explain a little more about where i am coming from)

Cardio does not burn muscle - it burns caories, like any other exercise. During low intensity exercise, your body burns a higher percentage of calories that come from fat. HOWEVER, what's important is the total amount of calories you burn during a workout. High intensity training for cardio is a must for fat loss. If you burn 100 calories during low intensity "fat burning" cardio, and you burn 300 calories during higher intensity cardio, you are actually burning more fat with the higher intensity cardio. Trust me - it's about total calories burned. It's also important to build muscle through weight lifting, because muscle is more metabolically active, and having a high percentage of muscle gives you a higher resting metabolism.

Please don't stop doing cardio if you are trying to lose body fat! Doing high intensity cardio 4-5 times per week, and strength training 3 times per week will help you lose body fat. 

 

" Say 50% of that is fat, so the other 50% is coming from muscle"  

Wrong.  The other 50% is from glycogen, in other words the food you eat.  If you haven't eaten enough food to supply all the needed glycogen your body will burn fat to make up the difference.

The burning of muscle thing is probably the most overhyped topic to ever come out of bodybuilding.  That's where it started.  Basically, there was a group of amateur bodybuilders who were so obssessed about losing any muscle mass at all that all they ever talked about was what kind of cardio burns the least muscle, what supplements can you take to preserve muscle (note - the L Glutamine scam supplement arose out of this and is one of the most popular supplements today with no clinical evidence to support it), worrying about burning muscle at night, etc.  They started posting on the internets and it became huge.  The one thing I have learned about bodybuilding is that out of scientific theories and results, the group as a whole pretty much takes what they want and leaves the rest.

It's a joke.  You do burn muscle while doing cardio.  Even moreso with weights.  You burn muscle walking the dog.  But it's pretty much irrelevant because your body repairs it and rebuilds it if it needs it.  You are likely always burning combinations of fat, muscle, and glycogen at the same time.

I appreciate what trhawley is trying to say, but when one has burned up the glycogen in the system, that takes 20 minutes on an empty stomach and 45 minutes if one has eaten, your body begins to canabalize muscle unless its fed. Do all Pro runners may have a tall and slender build? Or is it a biproduct of their activity. My son is 14years old. He looked like a football player. He took up running to get in shaper for basketball. His dimeneor changed from a football players appearance to now that of a distance runner. I think that one doesn't have to look bulky by liftiing weights. Women, don't produce testosterone, rather estrogen and will not have a bulky figure like a male might.  Just my thoughts and opinion. Great topic.
M

I know you guys would just die without your hour of cardio like Shape says, but it's not the best way to burn fat. In fact, studies show that cardio plus diet does not burn more fat then just dieting. That's number one. Secondly, you do burn muscle if you are not actively trying to protect your muscles if you're just doing cardio and dieting. Obviously no one wants to believe that, and that's fine.

This is a good topic, one I almost started myself.  I'm reluctant to use weights even though I understand the benefits of muscle on metabolism.  I'd rather have that scrawny runner look than look like I have any muscle.  I wonder if running six days a week and skipping weights would actually work best.

This is a great idea if you don't want to  eat much and don't want to protect your bones later in life. Also if you're female, chances are you'll never build up that much muscle without a lot of hard work. You do strength training to keep your muscle, not to be "skinny fat" which a lot of runners are. Sure they are very thin, but many still have skinny versions of their fatter selves.

I suggest you get a book or video by Covert Bailey.  He has an MS in microbiology from MIT, and he explains the cell biology during exercise in a way that we can understand it.  He will explain, like eastside says, how the cell burns glycogen, fat, and sometimes protein (or all 3).

I've actually never seen a "scrawny" runner, at least not in high school. All the XC and track runners are lean--the boys are particularly skinny but still have a good amount of muscle on them.

Eastisde: So, this has been invalidated?

Immediately after strength training, protein balance is negative (indicating muscle loss) due to the big increase in protein breakdown and the marginal increase in protein synthesis
 -. Canadian Journal of Applied Physiology; 20(4), 480-486, 1995.

Did something change when I wasn't looking?  This state persists for a few hours before protein synthesis starts to climb and protein breakdown starts to fall, so within a 24-hour period the balance is neutral or a slight net positive. That's the whole point of post-workout nutrition, to stop the protein breakdown and facilitate the protein synthesis due to training.

 This is also why endurance trainees get in trouble, including the endless bouts of cardio that effing Shape prescribes.

Immediately after an endurance-training bout, muscle protein balance is very negative because there's both a big increase in protein breakdown and a big decrease in protein synthesis. ... In these athletes there remains a large negative protein balance for 8 hours or more after endurance exercise
 -Meeting Minutes - Canadian Society for Exercise Physiology; 2000

Can you say muscle go buh-bhyeee? Without proper post-workout nutrition anyway, 'cause net protein balance is negative  in endurance trainees because if this. Those 8 hours of depressed protein synthesis in endurance athletes means you guys need to chug a lot more protein than us lifters if you don't wanna lose muscle.

Not much of a problem for the average runner of course - a jog around the block or even a 5k is not the same as a distance runner in training who does a half-marathon every day, and sprinters probably come under the strength training header since they're doing brief spurts of anaerobic activity.

 Cyclists however can easily wind up with elevated protein breakdown - good thing you guys tend to drink lots of sugar water (sports drink). Insulin inhibits the breakdown of muscle protein...

 And you do want to replace the glycogen stores pretty much immediately for optimal sports performance(Sports Med; 21(1), 7-17, 1996.) - it does make a difference for both us lifters and you endurance guys.

Plus, if glycogen stores remain remain low, muscle protein breakdown can result and lead to loss of muscle mass (Journal of Applied Physiology; 48, 624-629, 1980) - again not neccesarily a concern for the once-around-the-block amateur, but for the long distance/long duration crowd who spend hours on the elliptical, definitely. And for us lifters who're paranoid about losing muscle mass? Well, you know already - though it's actually much less of a problem for us.

 But the summary is that technically saying cardio burns muscle is a misnomer - it's the post-workout elevated protein breakdown and depressed protein synthesis that makes you lose muscle mass.

But it's a good enough lies-to-children version of what actually happens that I'll keep on saying it as a shorthand for this post.

(For optimal post-workout nutrition, endurance athletes should  consume a protein+carbohydrate mix every 2 hours post-exercise for 6 hours. That is, immediately after exercise, and at 2,4,6 hours afterwards.  ( American Journal of Clinical Nutrition; 72, 96-105, 2000. & 72, 106-111, 2000.)  I'd rather just lift heavy and have my one post-workout shake, thankyouverymuch.)

Melkor, you keep quoting Canadian sources... like that means something. ;-)

 

Seriously though, you said yourself that applied to endurance training and marathoners. Most of us that are just jogging a few miles or walking a 6 miles aren't going to burn muscle. Most burning muscle applies to extreme starvation or extreme endurance training. I don't think it applies to most of us with a lot of extra fat for the body to use, which is fats purpose. Right?

your body does not burn muscle for fuel, it will burn the amino acids that support muscle growth, that's where the problem is, all bodybuilders do cardio to lose fat for contests, but we increase our protein intake to prevent a protein deficiency. the only way to get your body to truly use muscle for fuel, is to starve yourself to death. if you keep your protein intake high enough, you will hardly notice a diff. in muscle mass.

Melkor, that was an epic rewrite of this:

http://www.johnberardi.com/articles/nutrition /puzzle_1.htm

But even he says:

"With this explained, I'd like to get back to the original objection. I believe that since the average trainee isn't training with the high frequency and intensity that could lead to large and persistent losses in muscle mass and metabolic rate, he or she has very little to worry about in terms of losses of muscle mass and metabolic rate. "