aerobic exercise and muscle atrophy

Can anyone tell me the specific physiological mechanism(s) by which aerobic (oxidative) training induces muscle atrophy and impairs strength development? Also, is there a certain volume of aerobic training beyond which these changes occur and below which they do not occur?

another factor is aerobic exercise over 90 minutes requires BCAA to continue, if you dont suppply them, your body takes them from muscle tissue. so if you are doing alot of long slow distance training, not only are you suppressing test levels (see a study posted by carson last week) but you are using your muscle tissue as fuel.

im kinda talking out of my a$$ here, i dont have a study on hand to back this up, but when i was still a triathlete, i seem to remember reading this. ill search for some resource for this to back it up.

It is not that aerobic exercise causes muscle atrophy, many factors play into this. For one, it is when the aerobic exercise is taken to a level where caloric intake doesnt meet the demands of tissue breakdown and chronic increases in metabolism. Protein catabolism occurs with repeated foot-strike, especially if the running occurs on hard surfaces (pavement). Also, strength/ power gains will level off and decrease since CNS work will be limited since high intensity work will not be done at 100% if high volumes of aerobic work is being performed. Also, as Charlie says “form follows function”, so your body naturally wants to weigh as little as possible if you are in endurance sports.

As a result of the pre-workout BCAA supplementation, degradation of proteins inside the quadriceps muscles was considerably reduced during exercise. This is a potentially positive effect, since proteins broken down during exercise must be replaced before subsequent workouts so that an athlete can continue training at a high level. In other words, BCM intake before exercise may lead to a lower requirement for muscle repair after a workout - and a quicker recovery from a strenuous exertion.

there is quote from a study that backs up (to an extent) what i said in my above post and underneith is a link to a summary of a couple of different studies that talk about BCAA.

You are correct Nightmare
I dont have the studies either, but these are factors. I remember reading once that male distance runners have a higher percentage to produce female offspring (I believe due to Test. levels) and if you notice, they are usually thinning up top.

Aerobic training also raises cortisol, and therefore, lowers the testosterone/cortisol ratio significantly.


there´s been a far bit of research into this topic, or at least into the topic of interference of concurrent aerobic and strength training. The mechanisms are not too clear. But check out these articles, and you can also check the references of these articles.

Maybe we need to define what is meant by aerobic training in this case. Are we talking about tempo, or high intensity VO2max work, or LSD, or…

It seems to me that once again a discussion comes around to illustrating the wisdom in Charlie´s system. Tempo is important, but at low intensities. I haven´t read much of the newer stuff (research) on the interference of aerobic training on strength, but the older studies simply over trained the subjects IMO with volume and the intensity of the aerobic work was too high.

Charlie is very careful to avoid over training and uses tempo to his advantage. Charlie has shown that they go hand in hand when used correctly.

Intensity is the key to avoiding interference. If you are talking about other sports, you have to prioritize the training in terms of what you want to accomplish, or what you want to avoid.

this article was published in the
july 2002 issue of muscle media. thought the group may find it interesting:

"If you’ve sworn off cardiovascular exercise because of its supposed
deleterious effects on muscle growth, your convenient
“out” has just been banished to the scrap heap of lame excuses.
According to new research published in the respected journal
Medicine and Science in Sports and Exercise, intense aerobic
activity performed three days a week, concurrent with weighttraining
exercise, does not seem to impair muscle growth or
In the study, 30 healthy male subjects were randomly
assigned to one of three training groups that performed 10
weeks of high-intensity strength training (45 minutes a day,
three days a week); intensive cardiovascular exercise (20 minutes
a day, three days a week); or concurrent strength and cardiovascular
exercise (three days a week, respectively). Results
showed that both the strength-training-only group and the
concurrent strength-training and cardio groups experienced
similar increases in quadriceps and hamstring strength and
hypertrophy (growth) with, surprisingly, the concurrent group
experiencing 4 percent more growth in type II muscle fibers
in the quadriceps. “Our findings indicate that concurrent performance
of both strength and endurance training does not
impair adaptations in muscle strength, muscle hypertrophy and
neural activation induced by strength training alone,” write
Dr. J.P. McCarthy and colleagues from the University of
Wisconsin-Madison. “The results provide a physiological basis
to support several performance studies that consistently indicate
three days a week of concurrent training does not impair
strength development over the short term.”


I wasn´t trying to say that aerobic training should be banished from a program. See above.

Also, my post re: testosterone and endurance training was also not intended to condemn it or endurance athletes. Like anything, a little does me good, a little more may be better, but that doesn´t imply that lots will be even better.

I was thinking more about the misguided people who want to reduce BF% and so do 50+ km running per week to get lean.

As far as the study by McCarthy, one has to interpret it very very carefully. Look at the subjects used. They would probably benefit from ANY training program. I would not try it with athletes or even very fit individuals trying to get fitter.

McCARTHY, J. P., M. A. POZNIAK, and J. C. AGRE. Neuromuscular adaptations to concurrent strength and endurance training. Med. Sci. Sports Exerc., Vol. 34, No. 3, pp. 511-519, 2002.

Purpose: The purpose of this study was to examine muscle morphological and neural activation adaptations resulting from the interaction between concurrent strength and endurance training.

Methods: Thirty sedentary healthy male subjects were randomly assigned to one of three training groups that performed 10 wk of 3-d·wk-1 high-intensity strength training (S), cycle endurance training (E), or concurrent strength and endurance training (CC). Strength, quadriceps-muscle biopsies, computed tomography scans at mid-thigh, and surface electromyogram (EMG) assessments were made before and after training.

This is for me a classic example of the standard University study - sedentary subjects or P.E. students - what can you really say afterwards?

I am not dead against the Body for Life program - I tried it myself a couple of years back after too many sad moments looking in the mirror, and it worked great for me. But I would not call myself an athlete anymore.

I’ll take the bait…

“Combining resistance and endurance activities apars to interfere primarily with strength performances at high velocites of movement. When strength & endurance training are done in excess maximal power performances is blunted. Possible explanations for the less-than-optimal strength-and-power development include adverse neural changes and the alterations of muscle protein in the fibre” (Kraemer, 1994)

Two points, in particular, I noted from this:

  1. aerobic activity has a particular impact on “strength performances at high velocites of movement”. While limit strength impact may not be huge, the impact on other activies down the force/time curve may be more dramatic.

  2. aerobic activity must be “in excess”. This addresses the second part of Brian’s original question.

What does this mean? I would imagine that this level of excess would vary from sport to sport. What may be an excessive volume of aerobic work for a 100m sprinter may not be excessive for a soccer player. It varies. Charlie states:
"Low intensity work will not lower testosterone levels unless the demands of effort and volume far exceed the conservative threshold proposed by me (75th percentile for no more than 2200 meters/ session) "

For a 400m sprinter this level is pushed out even further to 3000m per session/ 9000m per week.

For the lab rats, also check out:
Dudley, G.A., and Djamic, R. Incompatibility of endurance and strength training modes of excercise. Journal of Applied Physiol. 59: 1446-1451. 1985.

Dudley, G.A., and S.J. Fleck. Strength and Endurance training: are they mutually exclusive? Sports Med 4:79-85. 1987.

:wink: carson and GF

i was just stirring the pot alittle. dont laugh at me but i just got a copy of the “10 years of muscle media” on CD-rom, so im going to be full of little interesting tibits.

as i guy that has gone from one extreme (ironman training) to my current thought as “any thing with a corner is long distance”, i much perfer taking anything cardio in moderation. everything feels and works better, t levels are way better and ironically, my body comp is better now (doing 20 minutes of cardio a week) than when i was doing 20+hr/week.

How about Nightmare’s “thought of the day” from Muscle Media. LOL.

On this topic, for athletes invloved in sports with a high strength and endurance aspect (does it exist?), Zatsiorsky reccomends alternating cylces of strength or endurance emphasis. He went into quite some detail on it but its Friday, my brain is sore and the memory isn’t the best…