Reversibility in Sport is a very understood phenomenon, but it is no less worrying because it is understood. In fact I found three spellings on my spell check, and so got even more confused. If you want it in one sentence, "it's better to keep doing something otherwise you forget how to do it". Now then I am generally doing a lot even when I am not even climbing 8a, but if I am not doing 8a, how can I do 8a?
Well, and it is very complicated, but a hard climb is often the same as a an easier climb with smaller holds! It can be that simple, but small holds or sloping holds are not a simple thing of simply pulling up.
Unfortunately technique plays a huge part, it's the submerged part of the iceberg. Above is a photo of climbing in boots, light Alpine boots, the techniques to placing the foot and pushing are so different to friction on a pair of slippers as to feel like a different sport to many. When I climb in boots like these I always come back to rock climbing way better. But if I stay climbing with these I just get good with these boots, and forget friction smearing, and pushing the rubber into the features.
Lots of things are reversible, some things are not, you could say they are reversible in both directions, but you would have no front and back then. High standard rock climbing although a narrow band of the broader mountaineering has an immense number of parts which constantly need using, otherwise they reverse back to a lower level. People sometimes can only climb on one cliff, because it has crimps or pockets, but not on another cliff. 9a climbing doesn't translate into high end crack climbing. This may all sound obvious but it's amazing how people forget this.
My message is unless you have a very special task, try and keep hold of your skills, muscle memory and whatever stamina and power you have. Or at least stay in contact with it.
A good example of all this was when I went on a 40 meter pitch that had loose rock, crumbling (even more disconcerting), biggish run outs, a 7c+ bit on finger jams that hurt, and finished with a nice crack. Wow, by the time I got to the top of that I was a mess. A real mess, bleeding, bruised and battered, the rope had taken a severe work out too. Yep I was out of touch with my skill sets. There you go, but knowing these things doesn't protect me. You have to protect your skills and muscles, and energy systems, otherwise they fly away.