Does cardio build muscle?

By Marwan / July 9, 2014

Does Cardio build muscle? There is a lot of talk about whether or not cardio wastes muscle or builds muscle.  That last statement will definately shock a few people! Before we talk about how cardio can build muscle lets start by looking at reasons for some of us choosing to do cardio.

Here are some factors:

Goals – What your goal is, building muscle or losing fat or both

Body type – Certain body types need to do more cardiovascular training than other body types so an endomorph generally would need to do more cardiovascular work than say an Ectomorph.

Reasons – similar to goals, is it conditioning for a specific sport or just general conditioning?

OK, so now that we have established the factors let us talk about whether cardio builds muscle or burns muscle.  The answer is not as home and dry as some some would suggest.  There are several factors to consider as to whether or not cardio builds or burns muscle.

Firstly we need to look at the different types of cardio which are

Low Intensity – the least likely to have an affect either way, you can go on for a long time without ever really tapping into your glycogen stores

Moderate Intensity– the least likely to build muscle but can waste muscle.

Whenever I go to the gym I see people doing “steady” cardio.  They seem to think that steady cardio taps into their “fat stores” which they think will help them burn fat!! How wrong can they be!  You see whilst steady cardio indeed does tap into the fat stores, it is overall calories burned that will really help you drop down body fat %.  Also long spells of steady cardio does promote the release of cortisol (the stress hormone) which wastes muscle and increase body fat.  Have you ever seen marathon runners with muscles?

High Intensity– The most likely to build muscles and burn fat whilst also most likely to waste muscle depending on duration and intensity and available energy.

High intensity cardio will burn more calories after you stop exercising.  Research shows that the body can burn calories up to 72 hours post exercise after High Intensity Interval Training.  HIIT increases fat oxidation as it causes a greater increase in the hormones that speed up fat metabolism namely growth hormones, catecholamines, Epinephrine and Norepinephrine.

HIIT training also increases the uptake of the Glucose Transporter GLUT-4 (helps uptake the nutrients to the muscle cells).  HIIT also uses more muscles in the body.  Arms pumping, heart pounding to pump more blood around the body, knees and hip flexors.  The more nutrients are delivered to the muscles the faster they recover and the faster they grow!!

I tend to see a lot of people doing hours and hours a week of LISS (Low Intensity Steady State Cardio) and according to calculations they should be losing pounds, but they can’t lose anything because your metabolism adjusts to low intensity exercise. It just doesn’t cut it because it’s just a calorie burn at that time, not 24 hour energy expenditure. If you do LISS all the time, you’re basically trading calories in and calories out and you can cut these same calories through diet and still get the same effects.

A study conducted by Wilson et al. From the University of Tampa, FL, shows when you add in LISS you get a temporary boost in weight loss. Subjects lost a couple of pounds the first week and after that they lost nothing. This happened because their metabolism completely adjusted to that and that became their new set point to what they had to do just to maintain. LISS with a low calorie diet is terrible for fat loss and could cause muscle loss. During a low calorie diet, LISS cardio is more catabolic (muscle wasting) towards muscle as opposed to HIIT cardio being much more muscle sparing.

So can HIIT burn cardio? The answer is yes it can and I will explain why.  There are 2 ways that muscle can burn glucose (blood sugars) and that is through aerobic work (with air) and anaerobic work (without air). For example, long bouts of LISS cardio is considered aerobic work and weight training or HIIT cardio can be classified as anaerobic work.  Energy is released when ATP is broken down, energy is required to rebuild or re-synthesize ATP (Adenosine TriPhosphate)

  • Anaerobic system (Lactic Acid system) – Predominates in supplying energy for exercises lasting less than 2 minutes. Also known as the Glycolytic System. An example of an activity of the intensity and duration that this system works under would be a 100 m sprint.
  • Aerobic system – This is the long duration energy system. An example would be running a marathon.

The human body’s primary source of energy would be carbohydrates in the form of glycogen.  Glycogen is stored in the muscles and the liver.  The second one is the fats and third would be proteins.
When is the best time to do HIIT?
I would recommend you doing HIIT either on your day off or away from your weight training session, either first thing in the morning or in the evening.  You can do it after a weights session but the chances are you would’ve depleted your glycogen stores by that time, and the intensity wouldn’t be there because of possible fatigue.  If you do just make sure you sip on a BCAA drink before you do any cardio.

How long should I do cardio for?
Again I would recommend no more than 15-20 mins if you are doing HIIT or LISS.  If you are doing HIIT for any more you may risk muscle loss and increased levels of cortisol.
The only time I recommend steady state cardio is after your weights session.  This is especially helpful for skinny guys, this type of cardio helps recovery from a weights session and rids the body of the waste toxins.

Muscle wastage doing HIIT will only happen if your body fat is really low enough in the 3-5% region and both the intensity and duration are high enough to burn through all the energy reserves.

Sprinter with Muscle
If you want to be like this guy above then do cardio that builds muscle. Do HIIT.

Marathon runners with little muscle
Or if you want to be like these guys above, cardio that increases your chances of losing muscle choose LISS.

My intentions weren’t to favour one form of cardio and bash the other, even though it sounded like that. My intent was to educate and notify you that times have changed and science is proving some good stuff with HIIT cardio. At the end of the day it’s up to you on what kind of cardio suits you best.

Having said that I WOULD recommend you do about 10-15 minutes of low to medium intensity cardio after your workout simply to flush out the toxins and the lactic acid from your body.  You will definitely feel fresher and your recovery will be much quicker.

So guys I hope you have learned from this article whether cardio builds muscle. Any comments leave them below.

About the author


Hi, my name is Marwan and I set up this site to help skinny guys and girls just like you to end their frustrations and have the body of their dreams. I believe there are no limitations to what mankind can achieve.