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Does Cardio Kill Your Gains?

Cardio has a reputation as a muscle waster. Is this true or fair?
In this short article, I’ll give you the truth…


Firstly, some level of cardiovascular fitness is required to build muscle. You need to be able to recover between sets and perform high volume weight training to build muscle as fast as possible.

Achieving this level of conditioning isn’t that hard. If you have an athletic background, play sports on the weekend, have an active job, or do a lot of walking you probably have enough cardio fitness to thrive on bodybuilding style training. Even better, if you have this level of conditioning, your high-volume workouts will be enough to maintain it.

But some guys love doing cardio. It makes them feel better. If that’s you and you want to include some cardio in your training then, read on…

For hypertrophy (muscle gain) the research seems to show that High-Intensity Interval Training (HIIT) is better than (Low-Intensity Interval Training (LISS).

HIIT is stuff like sprints. Something where you give an all-out effort for a short duration. We are talking about extreme efforts here. Not working “quite hard”. Stuff like 50-100m sprints, a 20s-bike interval, or 100m on the rower done at 10/10 effort, with sufficient recovery between intervals to keep quality high.

This is not a case of doing 60s on/60s off on the treadmill. That is not true HIIT as the speed/intensity of effort you can sustain is not sufficient to be classified as high.

That would fall into a third category called MISS or Medium-Intensity Interval Training.

MISS is probably the type of cardio most likely to steal your gains. I’ll explain why in a moment.

HIIT seems to challenge similar energy systems to hypertrophy style training and, therefore, results in similar adaptations.

For this reason, it doesn’t interfere with your gains too much. However, because of its high-intensity HIIT is very draining and hard to recover from. This should be considered when including it in your training. It should be considered in the same way as a bodybuilding style workout when it comes to its impact on your ability to recover.

You wouldn’t just keep throwing extra weight training sessions into your program and think you could keep recovering and that applies to HIIT too. So, be conservative with the amount you do. When it comes down to it you might have to choose between lifting weights of HIIT. The choice is yours but, remember, if your goal is to get maximally jacked lifting weights will be more effective than doing HIIT.

LISS can actually aid recovery if the intensity is low enough. A brisk walk for example, can flush out the metabolic waste of a hard leg training session and actually speed your recovery. In this case it can be an effective muscle builder in its capacity to improve your recovery status.

Running a marathon or competing in triathlons are also LISS. These are much more likely to have negative consequences on your muscle gain. So, if your goal is maximum size and you regularly run 10km (or similar activities) then be aware it will impede your progress somewhat.

MISS is probably to be avoided at all costs. It is high enough in intensity to interfere with recovery without giving similar adaptations to weight lifting and the duration is long enough to burn a ton of calories and have a net catabolic (breakdown) effect. Longer intervals (>60s), short time trial style efforts like a 1km row, or 1 mile run also fall into this category and if done frequently could well rob you of potential gains.

What about if your goal is strength?

If pure strength gain is your goal it appears keeping all cardio to a minimum is most effective. You simply want to be sufficiently conditioned to be able to recover between sets to perform your weight training with good quality. Given strength training focuses on lower rep ranges and long rest periods, the cardio requirements are very low so a minimum level of cardio fitness is easy to achieve by just being vaguely active. Walk to work, walk the dog, take a stroll occasionally? Yep you probably have sufficed cardiovascular fitness to benefit from strength training.

Practical Tip:
  • Separating cardio and weight training reduces the interference effect. Leaving at least 6 hours between each seems to be required to minimise any potential negative effects.
  • Doing the cardio on different days to your lifting is even better.
  • Cardio (LISS) in the morning and weights in the afternoon/evening is probably the best bet if doing both on the same day
  • If you have to do it in one session then try and perform the cardio afterwards using muscles that were not worked during the weight training. For example, do cardio on an exercise bike after training upper body or do some battling rope conditioning after leg day.


Factor in your cardio to your nutrition

If your goal is muscle gain then you need a calorie surplus. Your weight should be going up over time. If your cardio eats away at your surplus and actually puts you in a deficit then that completely defeats the purpose of your bulking efforts.


PS Cardio is a powerful tool for fat loss/cutting. I will cover how to best incorporate that in another article. If you want a fat loss plan that includes cardio and weight training in a manner designed to MAXIMISE Fat Loss but MINIMISE Muscle Loss then, email me tom@tommaccormick.com and I’ll give the preview of my 8-week fat loss plan.

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