When it comes to staying in shape, I believe inertia is the biggest obstacle. That first step is the hardest. Once you get to the gym or the pool or the ball court, whatever, once you start your warm-up, you are good. It might be hard, you might be tired, but generally, my experience is, that far, you will go for it, and after you are done, you'll be glad you did.
But, ah, that first step. That's where fitness gets made or broken.
In lifting, they tell you that if you take care of the big muscles, the little ones take care of themselves. It seems to be true, but sometimes, the little stuff is what trips you up.
There's a Safeway store about a block from my house. Three-four minute walk, counting the two intersections you have to cross, you hit them right. (And best you cross those quickly. The narrower one gives you eighteen seconds protected in the crosswalk; the wider one, you have twenty-three seconds. I walk fairly fast, and it takes me twelve seconds to make the narrower one, and seventeen across the wider street. People who move much slower have to dodge traffic given back the green light. I've seen folks take thirty-five seconds to amble across, and this is a busy four-lane street, speed limit going from 4o mph to 45 in the next block.)
Today, I needed to run by the store to get some milk for the cat. It was gray, drizzly, about forty, and as I stepped outside, I thought, "Hmm, maybe I'll just take the car."
For a round-trip under two blocks, and not really any faster in the automobile, time you crank it up, make the block and lights, park, get into the store and then do it the other way to get home.
I was tempted.
I decided to walk.
I think that's how physical decline sneaks up on you. Well, you think, it's cold and nasty out, I'll just drive over, no big deal. And it's not a big deal, but once you default to taking the car instead of hoofing it, then some other small choice will pop up, and having folded once, it is easier to fold the next time. You'll eat too much of something you really don't need. Skip a workout because you feel a little under the weather. Put off doing your exercise routine until tomorrow. No big deal.
Then you find yourself having a third beer and chowing down half a bag of Fritos, and wondering how come your pants have shrunk so much in the wash, why your belt needs a new notch, and how come you get winded going to collect the mail ... ?
Friends, rust never sleeps, and entropy is always hiding in the bushes waiting to pounce. You need to pay attention to them or they will get you. (Well, to be honest, they will get you anyway, eventually. But you can delay it some ...)