The Cardio and Muscle Conundrum – By Sports Scientist Ross Edgley

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When trying to increase muscle mass many athletes will avoid cardio like the plague in fear it will plunge their muscles into a catabolic state and eat away at all their hard earned ‘gains’. But research conducted at the Department of Health Sciences at Mid Sweden University in Östersund, Sweden shows that maybe the cardio room shouldn’t be as feared as first thought. Here we breakdown the science surrounding cardio and gaining muscle, the results of which will surprise you.

Cardio and muscle loss
But before we analyse the findings from the study conducted at the Department of Health Sciences at Mid Sweden University in Östersund, Sweden, let’s look at where this fear of cardio comes from. Well, firstly the small, lean and light physique of a champion Kenyan runner probably doesn’t fill you average athlete with confidence.

But you have to understand these are athletes that undergo intense and prolonged forms of cardio that will produce physiological changes within the body that maybe aren’t conducive to building muscle. As scientists from Ohio University in Athens discovered, stating long distance runners had a higher proportion of slow twitch muscle fibres compared to power lifters. Slow twitch muscle fibers are far better for endurance but are also smaller in size so aren’t going to have you busting out of your t-shirt any time soon.

Long distance runner

Also, an argument could be made based on research from the University of Carolina that chronic exposure to prolonged endurance training’ could lower testosterone, again not great for those looking to pack on muscle. But it’s unlikely you are a champion Kenyan runner. Also it’s unlikely you are exposed to ‘prolonged endurance training’ which is why the research from Sweden is so relevant.


The Study:

Interestingly researchers wanted to not only test whether cardio would reduce muscle size but theorized that it could actually elicit greater muscle hypertrophy than resistance exercise alone. Put more simply they thought cardio plus weight training would actually benefit muscle size, not kill it.


The Test:

To test this they took ten, 25-30 year old men and had them perform 5 weeks’ worth of unilateral knee extensor exercises. On one leg they performed a 45 minute cycle and coupled this with 4×7 maximal concentric-eccentric knee extensions. So that’s a 1 legged cycle with 7 reps of knee extensions performed at about 75-80% of your 1 repetition maximum for 4 sets. The other leg was only subjected to 4×7 knee extensions.


The Results:

After 5 weeks of training scientists then used magnetic resonance imaging (MRI) to assess the cross sectional area and volume of the quadricep femoris (a muscle located at the front of the leg) and biopsies of the vastus lateralis (a muscle from the side of the leg) to determine the cross sectional area of the muscle fibres themselves. Results showed in the leg that performed both cardio and strength training, quadricep femoris volume increased by 14% compared to 8% in strength training alone. Also muscle fibre size in the vastus lateralis increased by 17% in the cardio and strength training leg compared to 9% in the strength trained only leg.

 Emma Storey-Gordon HIIT

The Conclusion:

Scientists in Sweden concluded that cardio combined with strength training showed a more robust increase in muscle size compared to strength training alone. When looking at how it does this, there’s a few possible explanations. Firstly cardio is probably the quickest and most efficient way of increasing the number of capillaries (small blood vessels) that network through the muscles. Increase their number and you increase the body’s ability to transport oxygen, nutrients and hormones to the working or recovering muscles. Cardio has also been found to improve insulin sensitivity which is essentially how effective your body is at processing and using carbohydrates. Improved insulin sensitivity results in greater levels of carbohydrates and amino acids being taken up into the muscles leading to greater growth and fullness. Finally improving the efficiency of the cardiovascular system will also you mean you recover faster between sets and therefore have an increased overall workout capacity which again can load the muscles above their habitual level and stimulate more muscle growth.

So as a final thought, will cardio kill your gains? Not according to our Swedish Scientists and many Strength and Conditioning coaches around the world, it could actually accelerate them.

Ross Edgley
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