But research conducted at the Department of Health Sciences at Mid Sweden University shows there’s no need to shirk swimming, your weekly five-a-side game or even regular runs.
In fact, far from burning away the hard work you put in on the gym floor, the researchers found cardio can actually increase muscle size. Ten men aged between 25 and 30 were put through a five-week training programme. With one leg they regularly performed a 45-minute cycle and 7 reps of knee extensions; with the other they just performed the knee extensions. An MRI of both legs post-programme revealed the muscles in legs subjected to extra cardio work increased in volume by 14% and 17%, compared to 8% and 9% in the legs put through just strength work.
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Obviously, a regime inundated with endurance training won’t help you gain muscle. For one, University of Carolina research found ‘chronic exposure’ to prolonged endurance work could lower testosterone. But 30-45 minutes cardio a few times a week? Provided you’re eating enough food to fuel all your workouts, this could actually increase muscle mass. After all, cardio is probably the quickest and most efficient way to increase the number of capillaries (small blood vessels) that network through your muscles. And the more you increase their number, the more efficiently your body is able to transport oxygen, nutrients and hormones to working or recovering muscles. Essentially, cardio optimises the pathways your body uses to repair the damage dealt by your weights work.
Finally, cardio has also been found to improve insulin sensitivity, which governs how effectively your body processes and uses carbs. Improved insulin sensitivity results in greater levels of carbs and amino acids being taken up into your muscles. The result? Again, increased growth.
So don’t abandon your park runs or weekend football just because you want to add muscle mass. Cardio and weights can be perfect allies in your goal to build a bigger physique.