Muscles are sexy and functional. (There's nothing hotter than heaving a 25-pound bag of cat litter into your cart, right?) Well, add another bonus of brawn: mood booster. According to Swedish researchers, muscle has a special protective power against depression and anxiety.
In the study, researchers found that as rodents' muscle mass increased, the more they released an enzyme called KAT. This enzyme, explains Jorge Ruas, Ph.D., and the study's lead author, converts a metabolite called kynurenine—which your body produces when you're stressed (and which can lead to inflammation and toxicity)—into an acid that can't pass through the blood-brain barrier. Basically, this effectively short-circuits signs of depression and anxiety. The more muscle, the more KAT, and the greater the relief of symptoms. Their findings were confirmed in a small study of human subjects too.
While it's not known exactly how kynurenine works, people with depression or anxiety show high levels of it in their blood—and previous studies have shown that reducing the chemical consequently reduces the symptoms of mood disorders. Ruas says that while we typically think of depression or anxiety as being a problem just in our brains, other systems in the body are involved too. "This study shows how muscle talks to the brain." And since human muscle accounts for 30 to 45 percent of your body weight, activate more muscle will have great benefits, he explains.
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And while the rats did mainly cardio, Ruas says that any exercise that increases muscle mass would have the same benefits. So hit the weights, drop into the yoga studio, or get your Crossfit on. The important part of is the intensity at which you work out. Know that intensity will vary for each person depending on your fitness level, but a basic rule of thumb is that finishing the workout should be difficult.
And remember: It's just as important to work on reducing the stressors in your life that are contributing to any mood problems as it is to keep your fitness in check. For the best of both worlds, set up a workout that challenges you physically and has some meditative benefits too. Power yoga, for example, calms your mind—even while your legs are shaking.