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Eat Less or Exercise More? (Part 2) - The Best Cardio To Lose Fat & NOT Muscle

Updated: Jul 19, 2021

In our last post, we discussed how the focus of any fat loss plan is always going to be creating a calorie deficit via your diet.

Supplement this nutrition plan with a sound weight training program to sculpt your body and reveal that beach-ready body you’ve always wanted once the fat is melted away!

Weight training is not really going to help you burn a lot of calories so if you’re reaching the limits of what you can do with your diet, you’ll probably need to start doing some dreaded…


You’ve probably heard of the term anabolism, it refers to the building of cells, hence professional bodybuilders take ‘anabolic steroids’ to help them grow and build giant muscles!

The opposite of anabolism is catabolism, the breakdown of cells.

What you might not know is that too much cardio, especially certain specific types of cardio, can actually lead to catabolism, leading to the breakdown and destruction of your valuable muscle tissue!

This means that certain types of cardio can actually undo all your hard work lifting weights and going back to what we discussed in our last post, if you’re not careful, you’ll lose both fat and muscle, potentially harming your metabolism and leading to an overly skinny physique which might not be what you’d been hoping for if your objective is to achieve a fitness model-esque physique!

Jogging vs gym body shapes
This is simply a visual representation how different forms of training can influence the appearance of your physique and is in no way a commentary on which is best, we leave that up to you.


Our muscles, roughly speaking, are made of either fast or slow twitch muscle fibres.

Fast twitch muscles fibres are the ones responsible for generating explosive energy while slow twitch muscle fibres are less energetic and have more endurance.

It’s generally the faster twitch muscle fibres that we’re targeting when lifting weights to tone and sculpt our physiques.

To minimise muscle loss and allow you to even continue to gain muscle, you need to select a cardio modality that minimises fast twitch muscle fibre activity and is predominantly a slow twitch muscle fibre driven activity.

This means you should avoid cardio that requires you to forcefully move your body and is impactful to your joints!

If the exercise gives you that lactic acid burn in your muscles and makes you really out of breath, then it’s likely using those fast twitch muscle fibres and might induce catabolism causing muscle tissue breakdown!

Gentler forms of cardio, like simple walking, hardly activate your fast twitch muscle fibres and are predominantly slow twitch muscle fibre driven activities!

These are your best cardio choices to burn calories while minimising muscle loss, leaving your fast twitch muscles fibres untouched, rested and fresh for your weight training sessions!

So, with the science in mind, here are our recommendations for cardio modality of choice, form best to worst, to burn calories and get rid of that last bit of stubborn body fat without losing muscle:

1. Walking (Best)

2. Incline treadmill walking / walking uphill

3. Swimming / Elliptical machine (uses the whole body and not just your legs to burn more calories)

4. HIIT / Cycling (including Spin classes)

5. Jogging (Worst)

Sure - jogging will burn a tonne of calories but catabolism and muscle loss will be high, possibly taking you further away from your physique goals.

If you’re not bothered about losing muscle, joint impact damage or looking aesthetic, then jogging and HIIT might be right for you but for the rest of us, things are about to get easier, you can literally walk it off!

How Much Is Too Much?

Doing too much cardio, even the recommended types such as walking and incline walking, still run the risk of inducing catabolism and muscle loss if you do too much.

Your cardio should not leave you so tired and sore that you can’t train with weights effectively, if it is, then it’s time to ease off!

Here are some suggestions to keep your cardio on point:

1. If your cardio machine shows calories burned or you’re wearing a smart watch, avoid burning more than two times your body weight in pounds (lb) in one session.

For example, if you weigh 150lb then aim not to burn more than 300 calories in one session, doing so increases the risk of catabolism / muscle loss.

2. Keep cardio sessions short and sweet, anything more than 60 minutes in one session can induce significant catabolism / muscle loss.

3. Divide your cardio to make it less catabolic and more manageable.

For example, if you take a 10 minute walk after each meal, you can easily hit 30 minutes of cardio per day (in just 5 days you’ll hit the medical recommendations of 150 min of cardio per week).

4. Just moving around more in your day to day activities will increase your NEAT (Non Exercise Activity Thermogenesis) and burn more calories!

Get off the bus one stop early, walk around when talking on the phone, stand when doing stuff, take the long route, it will all add up and get you to your goals faster!

If for some bizarre reason you do want to lose muscle, say you feel your legs have become too muscular, then simply follow the opposite of the recommendations above.


Here are some suggestions for cardio timing to optimise physique results:

1. Perform cardio on non-weight training days to minimise the negative impact it might have on your aesthetic physique goals.

2. If you’re strapped for time and have to perform all your training in one session, perform your cardio after your weight training.

If you perform your cardio first, you run the risk of being too tired to lift optimally.

3. People usually feel less hungry while performing cardio and for a while afterwards.

If you time your cardio so you perform it as far from your last meal as possible and just before when you would normally start to feel hungry, you might be able to keep your hunger at bay longer which in turn will allow you to further increase your calorie deficit and achieve your fat loss goals faster!

You do not have to wake up at 5am to perform your cardio on an empty stomach, this has been researched thoroughly and you’re not going to burn more fat by doing this!

Done & Done!

So there you have it folks, the key to achieving that beach ready body is to trim up with a nutritional calorie deficit, sculpt up with some weight training and walk off anything that’s left!

The next time you see those joggers, remember - it’s all about training smarter – not harder!

Thanks to the science, we know why the tortoise beat the hare!

See you at the beach!

Dr. Bobby Stryker

Team Flow

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