everything wrote:didn't even know all those distinctions existed. more interested in it for TCM theory curiosity. if those who can "do" make some distinction in meridian type for their yi->qi-> jin skill, though, then my curiosity is more IMA-oriented. we know sprinters have "fast twitch" "li" and marathoners use "slow twitch" "li", but doubt those athletes think about it or need to know too much theory on the fibers they use to win races.
In my teacher’s book he’s written 脈筋 Maijin. There’s 12 of them and have the same name as the acupuncture meridian that is in the same area. It’s a book about a qigong where you use open palms to pat your body and follow the meridians up and down the body, so you can’t really distinguish because they’re both being affected. So there isn’t much about them in this book other than that they’re invigorated from the Patting practice. They’re somehow related to growth, which makes me wonder if they come up more in pediatric tcm. I believe in the Bodywork and Tuina my teacher focused on that they were more significant because one would be able to feel the underlying structures of them. But I think in general a person doesn’t need to know them. Knowing about their existence and that there’s deeper connections running through the body is helpful to obtain “One part moves (Dantian), every part moves”. But intimate knowledge of them is probably more useful in tcm.
Speaking about the slow twitch and fast twitch muscles, in the Zhan Zhuang we do we first try to gain somatic control over muscle pairs and being able to isolate muscle tautness. Like activating only one half of the Transverse Abdominal muscles while the other half is relaxed. Fully separating the triceps from the biceps. Quads from hamstrings and so on. We also try to only activate the slow twitch fibers and keep the fast twitch fibers relaxed. The slow twitch fibers can last longer but in the Krebs cycle there’s a molecule Acetyl-Co-A which is depleted in a muscle group around the 6 minute mark. This is why we switch sides after 5 minutes because you never want to completely exhaust it. Fast twitch run out of energy around 90 seconds, so you have a 3.5 minute window where you can increase focus because you know it can only be the slow twitch fibers doing the work. As the slow twitch fibers get stronger the fast twitch are gradually trained to no longer get recruited for the simple work of supporting your own body weight. Which means that they can be preserved for fast dynamic movements while your slow twitch are holding your structure and resisting the pull of gravity.