Sound mind, sound body

I'm sixty years old and serious about physical fitness. Almost every day I get on the rowing machine and crank out twenty minutes at a sweat producing pace, do at least twenty minutes of brisk walking, lunges, situps, pullups, dips, pushups and more. I'm strong and healthy.

That's great, but I also believe in challenging my mind. I read a lot; science and history, almost never fiction and I'm constantly learning new 'puter stuff.. but how do you measure that?

When I'm on that rowing machine, I can feel the heat of my body and the sweat that comes with it. When I do those dips, I can feel the burn in my arms - I know I'm challenging my body. When I squeak out that last pullup I drop off the bar panting a little - I know it's hard physical exercise.

But how do we measure mental effort? Yeah, sometimes I can tell that I've worked hard mentally because I feel burned out at the end of the day and need rest. But I don't usually feel like that, so am I challenging my mind enough or am I just coasting? It's hard to tell, isn't it?

I've been thinking that I ought to do some things that I don't want or need to do - like learn Emacs (I'm a vi fan). Pushing myself out of my comfort zone in something I have to use every day (I write these posts with "vi") would certainly be a mental challenge, wouldn't it?

I think I'd also like to learn another language. I had a little French and a lot of Latin in school; maybe tackling Spanish would wake up a few lazy neurons.

What about you? Do you challenge your mind and your body? Any tips for either?