How does cardio cause muscle loss?

SLHysell

I see it mentioned here often that when you focus on cardio when losing weight, you lose muscle and fat. Does anyone have a sciency explanation of how that works?

prdavies1949

Its a load of rubbish promulgated by those who like to pick things up and put them down again. I have lost over 100lbs and believe me that was all fat. I now have more muscle than I have ever had and I haven't lifted anything. (Stands back and waits for flaming)

dannymacros

it all depends on your diet and routine.

20yearsyounger

My understanding is that when you are in a deficit you lose fat and some muscle. Cardio itself doesn't cause you to lose muscle. Resistance training helps you to retain some muscle you do have. You also lose muscle naturally if you don't use them.

auddii

20yearsyounger wrote: »

My understanding is that when you are in a deficit you lose fat and some muscle. Cardio itself doesn't cause you to lose muscle. Resistance training helps you to retain some muscle you do have. You also lose muscle naturally if you don't use them.

^This.

prdavies1949 wrote: »

Its a load of rubbish promulgated by those who like to pick things up and put them down again. I have lost over 100lbs and believe me that was all fat. I now have more muscle than I have ever had and I haven't lifted anything. (Stands back and waits for flaming)

^And was that verified by composition testing before and after or just going off that you can see more muscle now and are stronger?

Lasmartchika

prdavies1949 wrote: »

Its a load of rubbish promulgated by those who like to pick things up and put them down again. I have lost over 100lbs and believe me that was all fat. I now have more muscle than I have ever had and I haven't lifted anything. (Stands back and waits for flaming)

That's what I've noticed around here... if you're not lifting you're doing it wrong. And will never be exercising correctly until you lift. As if there aren't any other types of exercises besides lifting. (...Waits for beheading. :laugh: )

jrline

Muscles that don't get used do become weaker. As long as you are doing some strength/resistance training it will be minimal. I lost 100lbs doing cardio now I am doing strength training along with my cardio.

redfisher1974

The stuff we thought was gospel back in the 90's is now picked apart... I bet when we are gone and our kids are on here they will look at whats being said today and disprove all of it with the new gospel....Cheers.

tigersword

It's basic physiology. The human body actually prefers to save fat and lose muscle in a starvation situation (yes, dieting is technically starvation.) This is because the body can live much longer with fat stores than without them.

Average weight loss is about 75 % fat and 25% lean mass (muscle, water, bone, etc.) The larger the deficit, the more that ratio swings toward lean mass. Without proper fuel, cardio can lead to massive deficits that can lead to serious muscle loss.

Hornsby

When you lose weight, you lose muscle and fat. If you are doing nothing but running all day, my question would be, why would anyone think they wouldn't lose some muscles that aren't being used? It's common sense.

Holly_Roman_Empire

You lose some muscle with fat when you are in a calorie deficit regardless of what type of exercise you are doing. If you want to retain most of your muscle, resistance training is the most efficient way to do that.

sijomial

It's likely someone will lose some muscle along with their fat as they lose weight unless they take active steps to mitigate that.
Not because of the ridiculous idea that cardio burns muscle for fuel but often just because you are carting around a lighter body all day long.

Glycogen and fat are the preferred fuels and you have to go to ridiculous extremes with cardio (think repeated ultra marathons not running an odd 5k here and there!) to very inefficiently use muscle as fuel.
Another point often missed is that not all cardio is created equal - resistance based cardio can have quite different effects to running for example.

I suppose I should declare that I believe in a foot in both cardio and strength training camps for optimal results, 3x a week cardio (including some really long cycle rides) and 3x strength training worked well for me.

yopeeps025

prdavies1949 wrote: »

Its a load of rubbish promulgated by those who like to pick things up and put them down again. I have lost over 100lbs and believe me that was all fat. I now have more muscle than I have ever had and I haven't lifted anything. (Stands back and waits for flaming)

congrats on your weight lost but muscle atrophy does exist so just because you see definition does not mean you gain more muscle without progressive overload.

bold is 100% impossible.

leggup

Cardio does not cause you to lose muscle. Eating at a deficit will cause you to lose weight. That weight will come from fat, muscle, tissue, etc. Lifting while you lose weight will help you retain a larger percentage of the muscle you would otherwise lose during your deficit.

People who start out overweight/obese often have a lot of muscle (needed to carry around the excess pounds). A 300 lb person is literally carrying around 300 lbs every day. If that person starts losing weight, he's going to be carrying less and less. The muscles that were straining and working to carry around his frame (thus, working out those muscles), are no longer working as hard. He will lose that muscle slowly over time unless he adds resistance training designed to help him maintain some of that muscle. Muscle: if you don't use it, you lose it.

Jams009

It doesn't cause it, it just does little to prevent it, and in certain circumstances can increase it.

Being in a calorie deficit causes muscle loss (as well as fat loss) and cardio increases that deficit making the loss occur faster.

There's more to it than this, but one reason muscle is lost in a deficit is that muscle requires more energy to maintain than fat does. So when your body is in a calorie deficit it will burn muscle for energy as well as fat in order to reduce energy expenditure and therefore reduce the deficit.

Weightlifting also increases calorie expenditure and therefore the deficit, but unlike cardio it also encourages your body to hold on to the muscle (it thinks it needs it).

So a lot of people prefer weightlifting to cardio for fat loss.

A bit of both would be the ideal; weightlifting to keep the muscle, cardio to increase calorie deficit.

999tigger

20yearsyounger wrote: »

My understanding is that when you are in a deficit you lose fat and some muscle. Cardio itself doesn't cause you to lose muscle. Resistance training helps you to retain some muscle you do have. You also lose muscle naturally if you don't use them.

+1 thanks for saying it as its is.

belgerian

It also depends on how obese you really are depends on how much muscle vs fat you loose to begin with. Someone with 20lbs of fat will loose more percentage of that in muscle than someone with 200lbs of fat to loose.

kgeyser

britishbroccoli wrote: »

Cardio does not cause you to lose muscle. Eating at a deficit will cause you to lose weight. That weight will come from fat, muscle, tissue, etc. Lifting while you lose weight will help you retain a larger percentage of the muscle you would otherwise lose during your deficit.

^This. We all lose muscle as we lose weight. Resistance training helps retain lean muscle mass, but you also have to get enough protein while doing the resistance training. Someone posted an article showing the difference in muscle mass lost, but for the life of me I can't remember what the article was called. I think SideSteel posted it, I'll dig around in ETP to see if it's there somewhere.

Edit: I'm not sure if this is exact article I'm thinking of, but this article talks about the role of protein in preserving lean muscle mass while in a calorie deficit.

SLHysell

Jams009 wrote: »

It doesn't cause it, it just does little to prevent it, and in certain circumstances can increase it.

Being in a calorie deficit causes muscle loss (as well as fat loss) and cardio increases that deficit making the loss occur faster.

There's more to it than this, but one reason muscle is lost in a deficit is that muscle requires more energy to maintain than fat does. So when your body is in a calorie deficit it will burn muscle for energy as well as fat in order to reduce energy expenditure and therefore reduce the deficit.

Weightlifting also increases calorie expenditure and therefore the deficit, but unlike cardio it also encourages your body to hold on to the muscle (it thinks it needs it).

So a lot of people prefer weightlifting to cardio for fat loss.

A bit of both would be the ideal; weightlifting to keep the muscle, cardio to increase calorie deficit.

This is the most informative and thought out answer I've see so far. I bolded part of it because that is the part that I've always had a problem with. Why on earth would the body burn muscle instead of fat since fat's purpose is to store energy for use when we don't have fuel. The bold text sort of answers that, but the question that then comes to mind is, how on earth is running 5 miles not teaching your leg muscles and your core muscles that they will be needed? Why would your body burn those muscles up? Obviously you are making a demand on them. To me, it doesn't really jive with the theory that resistance teaches your body to keep your muscles because it "thinks it needs it".

EDIT: I did a couple of edits only to fix typos.

jeremywm1977

Jams009 wrote: »

It doesn't cause it, it just does little to prevent it, and in certain circumstances can increase it.

This probably sums it up best.
If you want to do only cardio like treadmill, elliptical, or running, and you enjoy it and can maintain such a routine, and such a routine has caused you to lose weight..........then great, you're already doing more than the next person doing nothing.

As far as the physiology behind your question. If, for instance, all you are doing is running, then over time you are going to become a more efficient runner. Unfortunately, your body is going to work to strengthen those muscles needed to run to create an improved economy of motion, but those muscles not used in your selected workout are going to atrophy.......you body will adapt to improve your selected method of exercise by burning the muscle no longer needed.

Yes, if you maintain a calorie deficit, you are going to appear more muscular-ish, but that is because the fat that previously covered those muscles is burning too.......it's kind of a lose/win.......you're burning fat, but you're also burning muscle which is probably a greater component in burning fat than that 30 minute run you just did.

In the end, do what you want, do what you can maintain and consistently do, and anybody who wishes to tell you you're doing wrong can just go away.

wolfsbayne

jeremywm1977 wrote: »

Jams009 wrote: »

It doesn't cause it, it just does little to prevent it, and in certain circumstances can increase it.

This probably sums it up best.
If you want to do only cardio like treadmill, elliptical, or running, and you enjoy it and can maintain such a routine, and such a routine has caused you to lose weight..........then great, you're already doing more than the next person doing nothing.

As far as the physiology behind your question. If, for instance, all you are doing is running, then over time you are going to become a more efficient runner. Unfortunately, your body is going to work to strengthen those muscles needed to run to create an improved economy of motion, but those muscles not used in your selected workout are going to atrophy.......you body will adapt to improve your selected method of exercise by burning the muscle no longer needed.

Yes, if you maintain a calorie deficit, you are going to appear more muscular-ish, but that is because the fat that previously covered those muscles is burning too.......it's kind of a lose/win.......you're burning fat, but you're also burning muscle which is probably a greater component in burning fat than that 30 minute run you just did.

In the end, do what you want, do what you can maintain and consistently do, and anybody who wishes to tell you you're doing wrong can just go away.