I've never been a big fan of the "muscle memory" concept. The brain runs the show, and practice is the key to learning.
I'm not a trainer, have received no "formal" shooting instruction since my Army days back in the 70s, so I MAY be misunderstanding the use of the term, but..
isn't "muscle memory" just the current buzz word term for what we used to call "training"??
The what, and how you do something once you have learned it to a level where you don't have to stop and think about what and how to do it??
I don't know about "speed shooting" a bolt action in matches, that's not my world, but I know a thing or two about what works for me for hunting and for fun.
It varies a little bit with different rifles, but the "open hand" method works very well for me, when speed matters. Also there is no reason to take the rifle off your shoulder, until you need to recharge the magazine.
Seen in in the real world often, and on the "silver screen" constantly, a supposed expert with a bolt action, taking it down from their shoulder, looking down at the rifle, then working the bolt.
I'm not a fan of checkered bolt knobs (for anything where rapid fire is even a remote possibility). The bolt knob should be smooth, so the open hand (palm, for most of us, fingers for some) can slip around it easily.
Open hand lifts the bolt handle, with enough of a cup (or curl) around to pull it all the way back, then flip your hand around the handle push forward, and down when closed. Takes much less time to do than say (or write).
No wrapping of fingers around the handle, no need.