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Aerobic Exercise Doesn’t Compromise Muscle Growth

Prior research has inferred that performing aerobic exercise (AE) concurrently with resistance training (RE) – specifically, if the RE was preceded by the AE – was contraindicated. The assumption was that the AE might limit the muscle building (myogenic) and protein break down (proteolytic) processes.

From the standpoint of developing strength, size, and speed enhancement – the mainstays of explosive sports like football – resistance exercise is a prerequisite to attaining these goals. Regular AE enhances the metabolic and morphologic processes that permit muscles to have greater resistance to fatigue, while increasing endurance and mitochondrial capacity.

It would make sense that RE and AE would be a match made in Heaven. However, research has reported that when AE was performed before RE – even with a time separation during the same day of concurrent training – there was a molecular interference in the mTOR (mammalian target of rapamycin) signaling pathway, which correlates with protein synthesis (muscle building).

Researchers in Sweden writing – “Aerobic Exercise Alters Skeletal Muscle Molecular Responses to Resistance Exercise” – which appears in the December 2019 issue of Medicine & Science in Sports & Exercise, chose to, “explore the effects of aerobic exercise on the acute molecular response supposed to control exercise-specific muscle adaptations to resistance exercise.”

The Swedes subjected one leg to aerobic and resistance exercise, which allowed for restored muscle function between bouts, while the other leg was exposed to resistance exercise only. It was hypothesized, “that aerobic exercise would interfere with the molecular response induced by subsequent resistance exercise.”

Nine healthy, physically active college student volunteered to perform a 45-min one-legged aerobic exercise (session) in the morning and four sets of RE for each leg 6 hours later. Hence, legs randomly chosen in a counter-balanced manner were subjected to either AE + RE or RE only.

Muscle biopsies were obtained pre and post RE sessions, which assessed muscle glycogen content, mTOR, and myostatin, which inhibits muscle hypertrophy (enlargement) – along with knee extensor (quadriceps) power.
The study concluded that, “in contrast to the posted hypothesis, it seems that concurrent AE + RE may enhance skeletal muscle anabolic environment,” which means that, “aerobic exercise can precede RE on the same day without compromising in vivo muscle power.”

The researchers point out that scheduling RE 6 hours after AE did not compromise the mTOR-related proteins. They do qualify their conclusion by commenting that, “it remains to be shown if cumulative exercise training, using the current paradigm, modifies chronic skeletal muscle adaptations, (i.e., muscle size and strength and power-related performance), compared with resistance training.”