If you asked me a few years ago what I thought about doing cardio when muscle building, I’d have quoted the following:

‘Never run when you can walk. Never walk when you can stand. Never stand when you can sit. Never sit when you can lay down. Never lay down when you can sleep’.

While this may be true at times, for most of you, cardio will have a place during muscle building. Here’s why:

Advantages of cardio during muscle building phases

 1.    Improved Recovery

When kept at low to moderate intensities, cardio can act as a form of active recovery. By pumping blood through the muscles after training them, many of you will experience enhanced recovery.

The common practice after a heavy leg day is to put your feet up for the next 5 days until the soreness and/or fatigue diminishes. But I’ve found that doing nothing at all can be counterproductive, and that by adding in low intensity cardio you’ll actually recover quicker.

One thing to bear in mind is that most forms of cardio are lower body dominant, so if you want to get the same benefit in the upper body, you’ll need to use different machines like rowers, skis or Airodyne bikes.

2.     Maintain Work Capacity

When training purely for muscle growth, it’s not uncommon to lose a lot of your work capacity and level of conditioning.  If your program is based predominantly around getting stronger in the 5 to 10 rep range with near complete rest periods (as most good muscle building plans will be), you’ll probably experience this loss in capacity pretty quickly.

With this drop in conditioning comes a reduced ability to recover both during and in between sessions. The fitter you are, the better you’ll be able to sustain quality volume, perform higher rep sets and maintain performance throughout a session.

If you’re that person who’s out of breath from a few sets of arms, you’ll need to be doing some cardio to have a decent level of baseline fitness.

3.     Increased Appetite

The response of appetite to exercise is largely variable from person to person. What I’ve found is that high intensity exercise like interval training or very hard leg sessions will blunt your appetite for a couple hours. On the other hand, cardio done at low to moderate intensity can help increase it – especially if it’s done first thing in the morning.

This can be a great addition for someone who is struggling to get enough food in.

4.     Improved Nutrient Partitioning

A potential benefit that’s not often discussed but worth mentioning is the ability to improve your nutrient partitioning, which is to do with where your calories ‘go’ to when you eat. In the case of muscle growth, we want more calories going to our muscles, and less to our fat cells.

The best way to trigger improvements in nutrient partitioning is training, especially weights and HIIT.

While we may want to limit HIIT during muscle building phases (more on that later), implementing it in a non-interfering way can help you to both stay in shape and keep you leaner during calorie surpluses.

On a similar note, keeping some cardio in your muscle building phases will allow you to maintain fat burning pathways, and some of the body’s ability to use fat for fuel. This means when it is time to cut (as you will need to at some point), your body won’t go through the ‘lag’ period it often has while it ramps up it’s fat burning pathways again.

5. Health 

The other factor at play here is the increasingly sedentary lifestyle most of us live.

Aerobic fitness has been shown to have strong links to health and keeping it at a good level can reduce your risk of certain diseases, such as heart disease. For this reason, I recommend that everyone does some form of aerobic activity on a regular basis, regardless of your goal. 

Potential drawbacks of cardio during muscle building phases

Despite the apparent benefits of adding cardio when muscle building, there are still some potential drawbacks you may want to consider.

1.    Losing Calories to Muscle Growth

While in theory this sounds like a clear problem for anyone with muscle building goals, this would only be applied to the extreme case of a ‘skinny ripped hardgainer’.

For everyone else, this is a non-issue, and shouldn’t deter you from adding a little cardio in to reap some of the benefits listed above. If you’re burning up an extra few hundred calories from cardio, this can easily be replaced in the day.

That being said, if you’re a skinny hardgainer, adding some cardio may help increase your appetite (which is typically very low). This could then be a useful strategy to enable you to eat in a consistent surplus. Give it a try and see if it helps or hinders your gains.

2.    Overtraining / Impaired Leg Recovery

The main concern I’d have with adding cardio into muscle building phases would be the risk of impaired recovery, both systemically (whole body) and locally (specific muscle groups).

However, this usually occurs in two situations – when it’s too excessive and too intensive.

Anyone who’s dieted hard knows the feeling of jelly legs you’ll get towards the end of a diet when you’ve been doing a lot of cardio for weeks on end. This is fine during fat loss phases, but if your goal is muscle growth, this may impact your ability to be progressive in the gym.

Most forms of cardio are lower body dominant, so if you’re someone who enjoys cardio and requires a decent amount during muscle building phases, you may want to consider rotating machines to keep the legs fresh.

So should you do cardio during muscle building phases...and how?

In my opinion, with the potential exception of the extreme skinny hardgainer, most of you will benefit from keeping some form of cardio in your training, year round.

The drawbacks discussed only come into play when the intensity and amount is too high. If it’s kept low to moderate, there should be no concerns.

Here are some guidelines that work well…

During muscle building phases, aim for 1-3 30-45  minute cardio sessions to reap the cardiovascular benefits, burn off a few calories and add some active recovery from your weight training.

The key is to make these sessions low to moderate intensity, with a maximum intensity of 60-70% of your maximum heart rate.

Now, if you’re someone who enjoys the high intensity work, I would cap it at once per week for 15-20 minutes. Any more and you may risk running into recovery issues.

I personally like to keep at least 5-10 minutes of high intensity work once a week in my own off-season training for the cardiovascular benefits, and to get my heart rate up really high.

When should you do cardio?

In an ideal world, you’ll want to separate your cardio and weight training.

If you’re training three or four days a week during a muscle building phase, I’d keep cardio to your off days.

If you train more often, then I’d aim to separate the sessions by at least 4 hours .

If timing is an issue, then you can also add it onto the end of your resistance training sessions.

Concluding the cardio and muscle building question

To sum up, I think the benefits far outweigh any potential negatives of implementing cardio during your muscle building phases.

The key is in the dosage, and not overdoing it. 1-3 30-45  minute low to moderate intensity sessions a week should suffice in allowing you to reap the rewards of improved recovery, work capacity, appetite, and nutrient partitioning, without running into any possible overtraining issues.