You already knew that exercise will give you those washboard abs. But did you know that it will also give you a washboa--ehem--quick-witted brain?

In 2004, neuroscientist Taeko Harada and colleagues asked whether there might be a direct link between aerobic exercise and cognitive functioning. So, they recruited a bunch of 27-year olds, and randomly assigned half to jog for 12 weeks while the other half did not jog. Then they were given tests of cognitive ability.

Not only did the joggers do better than the non-joggers, but cognitive performance in the joggers fell two weeks after they were asked to quit their jogging routine. Since then, a giant body of literature has emerged, linking aerobic exercise to all sorts of mental benefits, from problem-solving and attention, to stress relief and a reduced risk of Alzheimer's and dementia.

But don't just take my word for it, check out two great books on the amazing mental benefits of exercise: John Medina's Brain Rules and--for a more in-depth look--John Ratey's Spark.