Exercise doesn't just make you fitter. It also makes you smarter. Don't believe me? A whole host of studies prove that moving more leads to thinking better, which is a phenomenal thing to know if you're looking for a little inspiration to hit the gym. Still, it raises an interesting question: What exactly should you do when you get there?

If one of your primary goals when it comes to your fitness regime is to keep your brain sharp, should you spend long hours on the treadmill building your cardiovascular capacity? Are agility-promoting sports or dance classes better? Or how about pumping some good, old-fashioned iron? A new study offers some answers.

Bigger muscles, bigger brain

The research was focused on preventing cognitive decline and the development of dementia in older adults, specifically. It followed 100 people aged 55 to 86 as they pursued a specific fitness regime, measuring the effects on their brains through tests and MRI scans. After six months of training, the subjects showed not only improved cognitive function, but even growth in key areas of their brains.

What exactly were these folks doing? A simple, twice-a-week regime of weight training that involved lifting weights that were 80 percent of the maximum they could handle. This sort of resistance workout, it seems, not only grows your muscles, but also grows your brain -- literally.

The study's lead author, Yorgi Mavros of Sydney University, was so impressed with the results that he has recommend twice-weekly weight training for all who want to keep their mental faculties sharp as they age. In other words, all of us.

"The more we can get people doing resistance training like weight lifting, the more likely we are to have a healthier aging population," Big Think quotes him as saying. But the devil is in the details. "The key, however, is to make sure you are doing it frequently, at least twice a week, and at a high intensity so that you are maximizing your strength gains. This will give you the maximum benefit for your brain," he added.

Another proven path to a younger brain

Want more research-backed ideas on how to keep your brain functioning at its peak despite the passage of the years? Forget so-called "brain training" programs, which science has recently largely discredited, and instead think about taking up a simple meditation practice. Taking up mindfulness can turn the clock back on your brain, according to another recent study.