"Rust never sleeps;" and "Use it or lose it." Two old sayings worn smooth by time and repetition, but as true as they ever were.
Why mention it today? Two activities bring this up for me: First, a guitar piece, El McMeen's dropped-D instrumental arrangement of the old love song "The Water is Wide," which I used to could play from memory but now can't.
The other is how tight my hamstrings and low back have gotten because I haven't paid attention to keeping them stretched. Strong and flexible are better than either alone.
For me, loss of guitar repertoire happens because a piece stops getting played and fades from memory. In my case, it's because I started spending more time on the pieces I practice with the other old folks at the Closet Musicians' jam. When you have more than you can play in a single session, some of it doesn't get practiced.
There are folks who have immense repertoires, who can play a hundred songs without going blank on the lyrics or forgetting a chord change. And if you play a piece often enough and long enough, it does tend to burn itself into your memory. "House of the Risin' Sun," in A-minor is one that I should be able to remember after I'm dead, given how long I've played it.
Stuff I practiced for a couple years that I haven't played in a couple years? Not so much. Robbing Yarrow to play McCartney . . .
I have noticed that if I go back to a mostly-forgotten piece, muscle-memory sometimes will give me a nudge in places and my fingers seem to be able to do a five or six-note run on their own. Somewhere down in the mental junkyard, some portion of it is not completely rusted through.
Ditto the tight muscles groups. As long as I can do the physical things I normally do, the stretches to be able to do just a little more tend to get put onto the back burner. But what happens, insidiously, is that the djurus stop going quite so low, or the range-of-motion on a hoisted weight is maybe a hair less. It sneaks up on you.
Yesterday, you could bend at the waist and put your hands on the floor; today, you can't scratch your knee unless you sit down. Bad. Bad.
Do I need to be able to drop into a full split? No. Would I like to be able to do so? Sure. But the cost versus the gain is a factor; I'm not going there. However, there is a balance point and I do need to achieve that.
Fortunately, I know what to do to remedy both of these creeping forms of entropy and it's simple: Practice the stuff I want to keep, and take a little extra time during the workout to lengthen the muscles that have shortened.
There are three steps involved here:
First, you have to be aware that there is a problem.
Second, you have to determine the solution.
Third, you execute the remedy.
Easy to remember with the acronym: BAD SEX ...
"Simple" and "easy" aren't the same, of course, and sometimes that third step is a killer, but the three-step approach is useful for a lot of what you run into in your life.