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Cardio on Lifting or Non- Lifting Days?

June 05 2008

Endurance training (or cardio) remodels your body to be more energy efficient (or fuel efficient) - it is akin to a super car which gets better and better mileage, the more and the more you drive. On the on the other hand, strength training makes you faster, stronger and bigger but lowers energy efficiency (fuel efficiency).

What is the Problem?

Besides a few studies, most have shown strength adaptations to suffer when endurance training (cardio) is combined with strength training

There has been a few mechanisms proposed to explain this limit set by endurance exercise on strength gains.

  • Concurrent endurance and strength training can increase the workload and make you overtrained, and cut into strength adaptation.
  • Another mechanism is endurance training can convert fast fibers into slow fibers and reduce the number of fast fibers, which could play a major role in limiting strength and muscle development.
  • Glycogen depletion has been proposed as another mechanism behind this phenomenon. 

Now that I have introduced the concept and mechanisms, let’s go back to the question of whether cardio should be done on lifting on non-lifting days. The mechanisms above do not really help in answering our question because they are chronic adaptations and their influence doesn’t change with changing the days you do cardio. So the question remains - but not for too long:

What is the Solution?

ATP is the energy currency of a cell: Just how money is vital for us, so is ATP for a cell. We keep track of our money, but who keeps track of the ATP in the cell? This highly important job is done by an enzyme called AMPK, and it is rightly termed as the ‘energy sensor’ of the cell.

The good news is that AMPK is always activated with endurance exercise (bcos of the high energy or ATP needs for endurance exercise) and most endurance adaptations are purported to signal through AMPK. The bad news is that once AMPK is activated it shuts of anabolic events, like protein synthesis to prevent further loss of energy or ATP.

AMPK activation has shown in both animal and human studies (not yet conclusive in humans) to play a causal role in reducing protein synthesis. The blunting of protein synthesis during resistance exercise and after endurance exercise is now shown to be partly due to AMPK activation.


Figure1: Molecular representation of how cardio blunts strength training adaptations via AMPK

If this—AMPK due to cardio blunts protein synthesis—makes any sense,  doesn’t it make sense to keep your cardio and strength training as far apart as possible?

This would make a lot of sense sense if AMPK is activated and only stayed elevated for a few hours. Fortunately for us, AMPK in human studies has shown to have a short life, and tends to return back to basal levels after 1-3 hours of endurance exercise.


In short , AMPK blunts protein synthesis and cardio increases AMPK. So keep your cardio and weight workout far apart, like on seperate days or morning/evening.

Note: AMPk activation in muscle is localized as shown by one-legged training studies. So it might be better to keep your cardio adjacent to upper body lifting days. As well, have your high-intensity cardio days and strength workouts far apart since AMPk activation is time and intensity dependent. Again, having a pre-workout shake becomes all the more important considering that extra cellular events, such as glycogen, glucose, and creatine phosphate availability, besides ATP depletion, can negatively influence AMPK activation,

For endurance weenies trying to increase endurance adaptations, the approach of having carbs before and after endurance sessions may not be a good idea because they are inhibiting the activation and activity of AMPK, which plays a major role in endurance training adaptations. 

*AMPK: AMP- activated Protein Kinase
*ATP: Adenosine Triphoshphate

Reference 1

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Juarez | Wed April 21, 2010  

How long does it take for AMPk to become elevated with endruance training?  What sort of training elevates AMPk (is there something more specific than “endurance training”)?  Could long resistance training workouts using higher rep ranges and shorter rest periods also elevate AMPk?

Seymour | Sat May 08, 2010  

Hi Anoop

I was surprised to read that a fast twitch muscle fibre can become a slow one? When I was taught I was led to believe that we are born and will die with the same percentage of white and red muscle fibres. I was told that we could only maximise what we already had. Is this not the case?

I would certainly be interested to change some of my red to white!

I have a possible solution for those wanting to ensure they do not interrupt the muscle building process with their fat loss exercises. What if they undertook a strenuous circuit regime and focused mainly on partially anaerobic excursuses? If the exercises were varied enough, kept up for long enough (45/60 mins) and done 2/3 times a week would this keep AMPk production down.

It must be possible to carry decent muscle, be strong and still maintain high levels of fitness?

Look at Rugby players!

(really like your site btw)

Seymour | Sat May 08, 2010  

Don’t ask what “excursuses” are just make sure you do them anaerobically!!!


Ha ha LOL

Anoop | Sat May 08, 2010  

Hi Seymour,

Thanks for the comment.

Type 2x/B can change to Type 2A. You cannot go from Type 2 to Type 1 or vice-versa.

I am not sure I understand your question.

Yes it is possible to carry decent amount of muscle, be strong and still maintain fitness. I think the problem only shows up when you try to maximize all these variables. One of the adaptations has to give for the other.

Seymour | Sun May 09, 2010  

Thanks Anoop

I realised after posting what you were getting at. Makes sense, if you are looking at trying to put on 15lbs of muscle then training for an Ironman would be counter productive!

I only ask as I sometimes get carried away in both departments so I guess I need to focus on what results I want! I love heavy gym sessions but I also love swimming, cycling and running. Best of both worlds smile

When Type2x/B changes to Type 2A, probably a stupid question but is this reversible?

I should probably study more and pick my questions more carefully!

Thanks again and I appreciate your patience!

Anoop | Sun May 09, 2010  

Hi Seymour,

The Type 2X is the default muscle. If you stop working out, all Type 2A muscles goes back to Type 2x. Nobody knows why this is.

And you are fine. All good questions. You can register in the forum if you have more questions. There are more people to help you too there.

Patty | Tue May 11, 2010  

Hi Anoop,
What if weight lose (being 20-30 lbs overweight) is your main goal? I’m reading a blog on “what is best - cardio before weights or weights before cardio). I gave up reading as it went back and forth for hours. Now after reading the above - Maybe doing both at the same time is not best. I understand it invovles Priority of your goals.

Now - what if you only have 2-3 days a week (max 4 days a week) 60 min to dedicate to working out?

or - if weight lose is your goal and you only have an hour 2-3 days a week. Does it really matter that much?

and if muscle strength/growth and a 10 lbs weight lose is your goal - what is best?

Thanks - Patty

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