‘Cardio kills gains.’ It’s the gym bro myth that will not die. The statement has been around for decades and it’s one that many lifters still fear to be true today.

Is it true? No, not if it’s done right.

I used to avoid cardio like the plague. Then I realised in time that my lack of fitness was holding me back. Assuming that “gains” refer to one’s ability to get stronger and build muscle, doing too much can certainly “interfere” with progress. But so can doing too little.

 Why lifters need cardio

The truth is that a healthy dose of cardio will support your strength and muscle building efforts. It will also improve your health significantly. Aerobic fitness is one of the strongest predictors of longevity.

 Here’s a fun fact. weight training is mainly fuelled by the aerobic system. This is true of all activities that last more than 30 seconds and when you repeat short bursts of exercise (as with weight training), it becomes more and more aerobic.

 Consider this study that looked at the relative contributions of the 3 energy systems in repeated max effort cycle sprints. 

 The subjects did an all-out sprint for 30 seconds, rested 4 minutes and then repeated the all-out sprint. Notice that the contribution of the aerobic energy system (oxidative) went from 29% >> 44%! 

Now imagine a weight training session in which you repeat similar short burst exercise, not twice but around 20 times, with much shorter rest periods. It’s easy to see how the aerobic system will dominate very quickly and why your fitness will greatly impact your weight training performance.

Does cardio build muscle?

In a nuanced way, yes, cardio can help build muscle. When you build aerobic fitness, your body will undergo physiological adaptations that can mitigate fatigue and speed up recovery;

  • Your heart will grow bigger and stronger so that it is capable of pumping more blood (and therefore oxygen) with each beat.
  • You will build a bigger vascular network to deliver more blood (and therefore oxygen) to the working muscles.
  • You’ll increase the number and efficiency of the mitochondria (the power plants in your muscle cells) which use that oxygen to create energy.

Cardio benefits you and your gains in 3 key ways

Train harder, for longer

Handle the same weight for more reps, recover faster between sets and have more energy to push harder as the workout wears on. This adds up to handling more volume (reps x sets x weight lifted) which will give a more potent strength and muscle building stimulus.

Recover faster

After a workout, your body needs to swiftly repair and rebuild tissues bigger and stronger than before. This takes time and energy. A robust aerobic system speeds this process up. It ensures that the rate of recovery outpaces the stress of training. As the saying goes: train hard, recover harder.

Reduce injury risk

Nothing is a recipe for injury like “fatigue” + “heavy loads”. Fatigue impairs stability which increases your risk of form breaking down and becoming vulnerable to injury. The bigger your engine, the better you will mitigate fatigue.You will preserve good form and be safer.

How to do cardio without losing muscle

In the world of sports performance, doing “strength” and “cardio” training in the same program is standard.  The technical term for this is concurrent training. Almost every athlete follows a concurrent training program because most sports require a balance of cardiorespiratory fitness, strength and power. 

The challenge with concurrent training is that strength training can interfere with cardio performance /  adaptations and vice versa. The good news is that the “interference effect” (as it’s known) can largely be cut out if you are smart and strategic with your programming.

This means that it’s possible to reap the rewards of cardio and minimise the potential for it to slow down your strength and muscle building progress.

My own experience, before and after cardio…

Going back to my own experience, not doing cardio was holding me back. In the gym, I was constantly fatigued and had no “oomph” to push myself. My progress stalled. Outside the gym, I was tired and woke up drained very often, even if I slept 8+ hours.

Within a couple of months of including cardio in my training, my energy came back. I was sleeping better, recovering faster and pushing myself harder in the gym. Nowadays I train cardio 3 days per week and have done for the past several years. I’ts been a game changer!

How do you know what cardio training to do and when?

On the PRGRM App, you have cardio options in every program. We show you how and when to work that engine.

You’ll find out about:

  • The most effective cardio methods to support muscle & strength gains.
  • Methods to get your heart rate in the optimal zone.
  • How to schedule your cardio workouts relative to weight training (do the right work at the right time)