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Why You Bulk Up With Resistance Training, Not Endurance Training

Researchers find out how and why cardio falls short when it comes to building muscle.

Peroxisome proliferator-activated receptor-gamma coactivator PGC-1α. That’s the very long name of the gene activated by both endurance and resistance exercises. So, why do you bulk up with one and not the other? A study published in the American Physiological Society Press Release has the asnwer.

First, some not-so-general knowledge: Proteins turn certain processes in our body on and off, and make them faster or slower. Their duties and instructions are imprinted on sections of our DNA (genes), but proteins can come from the same gene and turn on other genes. Stay with us. When only one portion of a gene’s code is read, you have what’s called an isoform. Researchers have found that isoforms of PGC-1α exist and the specific isoform produced depends on the type of exercise someone’s performing. 

In this study, researchers at the University of Jyväskylä in Finland examined the isoforms present shortly after volunteers exercised and the genes those isoforms turned on. Samples were taken from the thigh muscles of healthy men after they performed high-intensity resistance exercises or moderate-intensity endurance exercises. 

The researchers found both endurance and resistance exercises produced isoforms PGC-1α exon 1b, PGC-1α exon 1b' and truncated PGC-1α, while only endurance exercise produced PGC-1α exon 1a isoform. In short, endurance exercise only activates genes that increase endurance capabilities (i.e. the growth of new blood vessels are stimulated), whereas with resistance exercise, you get new blood vessel growth along with the gene that promotes muscle growth. 

If you didn't really understand (or care about) any of that science, here's all you really need to take away: Next time you're at the water cooler, ask if your coworkers know why resistance training builds muscle while cardio does not. You'll wow them when you drop the fancy answer: It all has to do with a little gene called peroxisome proliferator-activated receptor-gamma coactivator. (We recommend practicing pronouncing this before you use it in real life.)

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