As if growing muscle isn’t hard enough, then try adding cardio into the mix. A lot of lifters I know tend to stay away from cardio altogether, the problem with this is that these guys can barely make it up a flight of stairs without going in to cardiac arrest. Cardio is incredible for keeping us fit and healthy, as well as being an amazing tool in helping us to lean down if that is your goal. The problem is that cardio often gets demonised and the confusion stems from statements like “don’t do fasted cardio, you’ll lose your gains”, “LISS cardio will eat your muscle” and finally, “don’t do cardio after training or it negates your gains”.

Today I want to put your mind at ease, clearing up what is fact and what is fallacy.

Here are the worst and best types of cardio for those who want to preserve or grow muscle.

Cortisol - The Crusher of Gains.

Cortisol has three main functions when it comes to training.

1. Mobilisation of energy. Cortisol frees up stored glycogen and fatty acids. In addition, it has the ability to break down muscle tissue as a way of creating the necessary energy available to fuel muscle contractions. The more energy you need to mobilize, the more cortisol you'll release.

2. Adrenaline. Need a motivation boost? Cortisol has got you! This stress hormone increases adrenaline levels by stimulating the conversion of noradrenaline into adrenaline. Doing high volume cardio or pushing yourself hard will generate a high cortisol production.

3. Blood sugar balance. When blood sugar levels are too low, cortisol and glucagon get released to raise it again. Why is that important? Doing cardio fasted means your body needs to mobilize fuel, which will raise cortisol to a greater extent.

If you are trying to preserve muscle, cortisol manipulation is key. Cortisol has a significant correlation with muscle mass; the higher someone's cortisol level, the harder time he'll have building muscle.

Cortisol has the ability to increase muscle catabolism, leading to a breakdown of the tissue required for amino acids to be transferred into glycogen (energy/muscle fuel), which is also known as gluconeogenesis.

High levels of cortisol can lead to an efficient immune system, leading to slower muscle repaid and impaired growth.

And the last way the cortisol can impact strength and muscle gain is that is increases levels of myostatin. Myostatin plays a role in how much muscle mass your body can build. More myostatin means more challenges when it comes to building muscle.

The key takeaway? The best cardio we can do is the one that induces the least amount of cortisol release.

As we saw earlier, the 3 cardio types we want to avoid as they raise the most cortisol are those that:

1. Are high in volume or require a lot of energy
2. Pushing to your max, and;
3. Doing cardio fasted.

The Worst Types of Cardio For Muscle Preservation

 The worst types of cardio are going to be those that combine one or more of the points above.

1. Fasted Interval Training

A LISS walk in a fasted state is fine, what isn’t fine is doing intense interval training on an empty stomach.

Why is a fasted walk fine however intervals are a no go? On a fasted walk, yes, cortisol is released, however the intensity and energy expenditure is low. A LISS walk isn’t going to require a lot of glycogen mobilisation or caloric outlay, thus, although cortisol may be release, it won’t excessive.

Intervals, on the other hand, a recipe for a cortisol bomb. Firstly, you’re fasted. Secondly, intervals require a large amount of energy mobilisation and thus more cortisol is raised. This becomes even worse if you have a prolonged duration of time you are doing intervals for; volume is also added in to this mix.

2. Fasted Steady State Cardio At Moderate Intensity.

Let’s use cyclists for an example but it could be jogging or any other moderately intense cardio. Hours on a bike with long, continuous bouts of energy expenditure and cortisol release. A recipe for muscle loss. When you are fasted, as we know, cortisol is raised, now you have an increased your caloric expenditure from low to high which will ramp up your cortisol levels, putting your muscles at risk.

3. Post-Lift Cardio

When you're lifting, the mTOR activation from the training contributes to gaining muscle. Endurance work and cardio, on the other hand, requires a significant amount of energy, leading to an increase in AMPK levels, which is beneficial for losing fat, however it can inhibit mTOR which can damage gains. Releasing AMPK after a big lifting session has the ability to diminish anabolic response to your session. Thus, it's best to avoid cardio that'll mobilize a lot of energy right after your workout.


The Best Cardio?

The best type of cardio for maximising your gains is one that requires you to go all out for a short duration or go slow for a moderate duration. 

1. LISS (low intensity steady state) Cardio
Fasted or non fasted is fine. A gentle 45-minute walk won’t elicit too much of a cortisol response. It burns calories, allows you to preserve muscle mass and can have positive effects on your emotional wellbeing.

2. Go Hard Or Go Home
Hill sprints, sled push, the assault bike… choose an option and get to work. Proper interval training means you give 100 percent effort for a short burst and take the necessary time to recover so that you can go again. I like to utilise 20-30 seconds on and then rest for 2-3 minutes, letting the heart rate fall back down. Opt for no more than 20 minutes total including rest time (about 4-8 sets total). The longer rest periods will minimize adrenaline, and thus cortisol, lead to a better performance, which ultimately leads to a stronger physiological effect.
There you have it; the king of cardio is the one that keeps cortisol down.