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WHY Is Cardio Catabolic?


I've been here for a while and read all the posts about how endurance work is catabolic and the devil for muscle gain. I've never actually seen why it is though. I tried search but didn't come up with much (feel free to flame if you can come up with the answer easily with search). I'm looking for an actual physiological breakdown as to why it is catabolic (surely it must be more than the expansion of energy), and what is the best way to minimise the catabolic effects. I play aussie rules which is played on grounds much bigger than soccer, rugby, and grid iron fields. Endurance is a key requirement.


im no expert by any means but i guess they're not trying to say that cardio is catabolic necessarily but that putting your body in a negative nitrogen balance is. the addition of long bouts of cardio will put your body in a negative nitrogen balance faster than weight training alone. i believe that as long as your nutrition is sound around these cardio sessions (i.e. taking in a moderate amount of protein before and after) you should not lose any great amount of muscle doing up to 30-40 minutes a day if you want. this may not be accurate if you're a true ectomorph. those guys have it tough. some guys put themselves in a negative nitrogen balance pickin up a pencil.


all strenous exercise is catabolic, i mean you are putting energy demands on your body. Which diverts blood away from the alimentary canal(inhibiting digestion) and supplying gases and releasing stored nutrients to tissue. This "releasing" is a catabolic process, thats the definition really of a catabolic pathway.

When talking about cardio being catabolic, people generally mean that long distance, or endurance cardio, tends to put an excessive amount of stress on your tissue. Excessive is relative, mainly meaning it really breaks down more than you'd want it to.

Apparently it is to my understanding that long endurance cardio trains the CNS in a similar fashion weight training does, but gears it toward a different goal. In heavy compound lifts, we put " too high" demands on muscle tissue, and the body responds in kind to maintain homeostasis- growth to prevent further microtrauma of those heavy weights.

In long distance running, you signal the body to gear towards homeostasis, but for endurance. Hence the body begins to shed excess weight(or read, inhibits- growth).

-Whether this second point is actually supported by evidence i really do not know.


from a high level perspective, catabolic = not growing. cardio = burning calories. to grow, you need calories. the more calories you are burning the harder its gonna be to get out of that catabolic state.


Insulin and glucagon conflict; you can't have both high. Aerobic work = increased demand for gluclose = more glucagon = less insulin (which is the primary anabolic hormone, depending on semantics).

Also, cortisol and testosterone seem to conflict; Aerobic work = more cortisol release = less available testosterone (and you know what that does) while cortisol is elevated. When doing long duration aerobic work, protein breakdown increases in response to energy demands and a couple other minor reasons.

Extremely simplified, but the full explanation is around here somewhere in search.



The different goal part is definately right, but what do you mean by similar fashion?



similar fashion in an extremely vague and general sense. Basically I meant that it also trains the CNS in response to training, as does weight lifting. I was not alluding to any mechanism of action or pathway.




But what if you drank a drink like Surge while you were doing cardio, would it still be counter-productive on a bulking diet? I'm on a bulking diet and I would love to reap the rewards of a healthy cardiovascular system but I'm hesistant to add cardio in some of my off days for fear that I'll be burning precious muscle.


haha man don't worry too much. Yes you can chug half a serving of surge about 15-20 minutes before your cardio session to take some strain off your body.

What were you going to do, run a marathon? You can still run for a bit(consensus is don't be afraid of a 20-30 min HIT session if you take some surge before it).

and it's kind of interesting though, the way people react to cardio and it's catabolism. I mean shit, if exercise was that rapidly catabolic, we'd be losing muscle as we trained.

Don't worry too much about it man, just don't turn into a track and field allstar and you'll be fine.


late reply i know..
with aerobic work,your body simply likes to break down protein for gluconeogenesis.this protein comes from your muscles obviously.its for this reason that an endurance athlete would actually require more protein than a bodybuilder since s/he wouldnt want to hit a brick wall in the middle of a race. if u take a look at the RDA for protein req's for athletes (and i know everyone on this site hates what the RDA has to say about protein reqs, you'll see its higher for endurance athletes than strength athletes.


Just decrease rest periods between sets to like 30 seconds.


I think part of cardio's negative image would be the fact that long duration exercise can convert type II muscle fibers to type I (fast twitch to slow twitch). Since type II have a much higher potential for growth, this is bad for weight lifters.

Also, I don't really have the specifics on it, but I remember reading that you can't develop maximal endurance and maximal strength concurrently, so that may play in.


I was under the impression that the reason it is catabolic is that as soon as your body has used up the energy it has stored from what you have eaten, it begins to take that energy from body stores like fat and muscle. The longer the endurance of the cardio, the more it uses the stored fuels.

I would do a search in the articles section for the answer to this. I am thinking there was a round table on it, but I am not sure.



Here are a couple of links I found...




Hope this helps...



While this statement is basically correct, it's more the reason long-duration aerobic work is counterproductive to strength athletes and bodybuilders than it is why it's catabolic. Technically, even lifting is catabolic as well until the anabolic response kicks in afterwards.



I'm going to jump in with both feet and see if I can't make a fool of myself...

1) Amino acids can be used as a fuel for exercise or other processes.

2) Levels of substances in the bloodstream are generally kept within certain ranges.

3) As the aminos in the bloodstream are consumed, the body will look to other sources.

I don't really know if the body attempts to regulate low amino acid levels in this way, but I think proteins are vital to many processes. Anyway, if so, it could help explain the effect of one set of muscles growing at the expense of another.


OK you want to reap the healthy rewards on your cardio vascular system. Do a multiple heavy sets of DL's, squats, etc and tell me your HR isnt throough the ROOF. You are training the cardio cascular system with weight training.

Heck get a tire and flip it a ton, do sledge hammer work etc.

Also not sure if it was mentioned but along with what was stated about cardio the de/retraining of the CNS, the tendency of it converting muscle fibers from fast to slow twitch, also the fuel used for moderate and higher cardio (running jogging etc) is glycogen. Once you replete those stores then the body turn to protein your muscle to make more. Hnce muscle loss.

Now I dont feel cardio should be GONE during a bulk just choose it wisely go hike with a back pack, do strong man stuff, a set of Heavy breathing squats, occasonal jogs, drag a sled, and keep eating. No reason to tunmr into someone who cant climb a few flight of stairs but if strenght and sixe is the goal a ton of mod and high cardio isnt your friend.

Ive been doing much of the above along with just tons of walkking Oh and short but intense sprints and my endurance capacity is still OK not the best its ever been but ok and Ive packed on a say 20+ lbs this year.


This doesnt necessarily mean you cant train for strength. Low rep stuff plus Interval training compliment each other well.


It sure is Jacross. Not really answering your question but this will probably be of interest to you. Most AFL and VFL teams are backing off on the long bouts of continuous endurance training in the off-season and pre-season. They are now doing 1km intervals. They basically do a flat out km followed by 5 minutes break. Repeat several times. I heard the Western Bulldogs did 16 of these Little wonder why there are so many ACL injuries with them.

The general feel with the coaches is that they are gaining aerobic fitness without losing too much quality mass.

The old 30-60 minute phartlek runs are a thing of the past for the AFL teams.