I’d love to run a couple of sessions, but it’s probably best to leave that to next year, unless someone specifically comes to me looking for one.
If we’re going to start talking about shock-loading joints and the like, imma need some more coffee, preferably Irished up…
The places you will always have tension are mostly your legs/feet and core. As soon as you’re standing on something less than a jug, you need to maintain tension in your feet to keep your weight on the holds, which can add up quickly, and with no core tension, you will flop about everywhere and severely limit your reach. Even just holding your core will often allow you to reach a hold you think you can’t. Ideally, you don’t really want your shoulders engaged the whole time, but it’s important that you know when to do so, such as in dynamic moves and anticipating just before you need them, to prevent injury as much as possible. However, particularly on overhangs, if you allow your shoulder to drop (ie. not locked) you will get much more from a rest, as you’re ‘hanging on your bones’ rather than having to use your shoulder muscles.
As I said several times, as super-complicated topic, which I’m not really qualified to talk about. These are just my thoughts on the matter, and not necessarily right or useful.