Will cardio ruin my muscle gains?

(Image credit: Unknown)

Do you avoid cardio at all costs? Many men who are trying to pack on muscle do, thanks to the widely held belief that that it puts muscle tissue in a catabolic state, which means it will eat away at your hard-earned gains. But in fact you shouldn’t fear cardio, according to research conducted at the Mid Sweden University in Östersund.

The researchers wanted not only to test whether cardio would reduce muscle size but also whether, as they theorised, it could actually ‘elicit greater muscle hypertrophy than resistance exercise alone’. Put more simply, they thought adding cardio to weight training could increase muscle size, not reduce it. To find out they got a group of subjects to perform unilateral knee extensor exercises five weeks. They performed a 45-minute cycle with one leg, and coupled this with maximal concentric-eccentric knee extensions, done in four sets of seven reps at 75-80% of their one-rep max. The other leg was only subjected to the knee extensions.

After five weeks, the scientists then used magnetic resonance imaging (MRI) to assess the area and volume of the quadriceps femoris (the muscle on the front of the leg) and biopsies of the vastus lateralis (on the side of the leg) to determine the cross-sectional area of the muscle fibres themselves. In the leg that performed both cardio and strength training, quadriceps femoris volume increased by 14% while in the leg that did strength training alone it increased by just 8%. Muscle fibre size in the vastus lateralis increased by 17% in the leg that did cardio and strength training, compared with 9% in the strength-rained leg. The researchers concluded that cardio combined with strength training showed a ‘more robust increase in muscle size compared to strength training alone’.

Why was this? There are a few possible explanations. First, cardio is a fast and 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 working or recovering muscles. Cardio has also been found to improve insulin sensitivity, which means it makes your body more effective at processing carbohydrates so greater levels of carbs and amino acids are taken into the muscles, leading to greater growth. Finally, improving the efficiency of the cardiovascular system also means you recover faster between sets and therefore have an increased overall workout capacity, which can load the muscles above their habitual level and stimulate more muscle growth. 

So add some cardio to your strength training and don’t worry about it having a detrimental effect on your muscle – in fact, your gains could actually be accelerated.

Ross Edgley is a sports scientist at The Protein Works. Click here for more information.

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Ross Edgley

Ross Edgley wrote for Men’s Fitness UK (which predated and then shared a website with Coach) when he was a sports scientist, working for brands such as Myprotein. Edgley went on to perform a series of physical feats, including swimming all the way around Great Britain in 157 days. He has written the books Blueprint: Build a Bulletproof Body for Extreme Adventure in 365 Days, The World's Fittest Book and The Art of Resilience, as well as contributing to publications such as GQ