In recent years, there have been some interesting studies showing that the acute anabolic signaling pathway may be blunted when aerobics and resistance exercise are combined. Previous research has observed only modest hypertrophy gains when endurance training is combined with resistance exercise. Therefore, scientists have suggested there may be an “interference effect” when cardio is performed at the same time as resistance exercise. Before you throw your treadmill out, it should be clear that these studies were done after one training session. Before we go any further let’s recap the original study. Researchers took trained men and assigned them to either one of two conditions: One experimental trial consisted of a bout of resistance exercise followed by a bout of endurance exercise (cycling) while in the other trial subjects performed the reverse exercise order (endurance then resistance exercise). Muscle biopsies were taken before, 15 minutes after exercise, and three hours after exercise. The results came out as “doom and gloom”—no matter how you look at it. Cardio before resistance exercise suppressed IGF-1 Ea (a gene splice of IGF-1) mRNA and also induced small declines in mechano growth factor (-27%). Resistance exercise then cardio increased genes for muscle tissue breakdown. For example, muscle breakdown genes were elevated Atrogin (21%) and MuRF (53%) mRNA. In summary, for the optimal anabolic effect, both resistance exercise/cardio together in close proximity likely results in an acute “interference” of key anabolic signaling pathways.
But again keep in mind this was a single study, the question is: Does long-term aerobic and resistance exercise blunt muscle hypertrophy? Well, in a recent issue of Journal of Applied Physiology, an interesting article titled “Aerobic exercise does not compromise muscle hypertrophy response to short-term resistance training” should put your mind at ease. The study was done for five weeks and tested the effects on combined weight lifting with cardio (45 minutes). It was interesting in the way that they performed the study, they used one leg for resistance exercise only while the other leg they used for resistance exercise and one-legged cycling. At the end of the study, there was no difference in the muscle sizes between both the legs measured. In fact, they found slightly greater increases in muscle mass with the combination of cardio and resistance exercise. The results suggest that aerobic exercise when combined with resistance exercise does not suppress muscle gains and may even be beneficial.