Many physique athletes stay away from cardio in fear that it will burn up their precious muscle.
A new study, published in the journal PLoS One, followed two groups of trained male subjects. One group switched off between performing continuous cycling (varying between 30 and 60 minutes,) or interval cycling (6-8×2 minutes,) before hitting the iron, while the other group only lifted weights and did no cardio. Both groups received a protein supplement immediately post-training. After seven weeks, the group that did the cardio experienced greater increases in lower-body muscle fiber size as well as more training-induced alterations that lead to hypertrophy. Scientists theorized that the cardio did not boost growth by inhibiting catabolism, but rather contributed to various anabolic factors that triggered muscle stimulation.