Amazing finding about exactly HOW exercise wards off depression, and why it might be a totally different pathway than antidepressant medications. Basically exercise seems to convert a chemical INSIDE MUSCLE CELLS from one associated with depression to one that is not. Instead of changing brain chemistry after the fact, it prevents this chemical from reaching the brain at all.

That is a fascinating finding. Chemistry wants us to exercise!

Within the muscles, endurance-type exercise prompts the activation of a protein called PGC-1a1. This protein does a lot already: It promotes the growth of blood vessels, increases the efficiency with which the cells use energy, ensures that fatty acids are broken down for the body's use, and guards against muscle atrophy.

But the authors of the latest study show that activating PGC-1a1 in the muscles also increases the production of kynurenine aminotransferases inside of muscle. And the presence of these enzymes catalyzes a chemical change in kynurenine, converting it into kynurenic acid.

In mice, and very likely in humans too, chronic stress increase levels of kynurenine in the brain -- and high levels of kynurenine appear to induce depression. But kynurenic acid can't get into the brain, because it can't get across the blood-brain barrier. So, when PGC-1a1 levels in muscle are high, and kynurenine gets converted into kynurenic acid, levels of kynurenine in the brain naturally drop.

How very interesting.

Engaging in exercise is great. But finding a way to mimic exercise's antidepressant effect could also be of "great therapeutic value" to patients who are not helped by antidepressants or who find hard exercise difficult, the authors suggested.

I wonder if in fact it is "hard exercise" that is needed, or whether simple movements every day could be enough. I'd also like to know if there's a difference (in this context) between anaerobic and aerobic acitivty.

The article doesn't say but I'm curious too. Time for more research!