The human studies we have on l-carnitine are oral and intravenous application. They haven’t been done on intramuscular, so we have to extrapolate - we know IM use tends to be similar in result to IV on many things, just slower release of the drug to the bloodstream.
Oral use cannot raise carnitine to supraphysiological levels; they fall rapidly after a spike. IV therapy DOES keep them elevated a substantial amount over baseline. You can’t keep an enhanced level with oral. And you don’t NEED to load IM carnitine; I never have. On the very first injection ever, I noticed I was sweatier & had better pumps, and felt like I had more energy to train. You can receive benefits from acute use, and will still reach an elevated saturation over baseline after weeks of use around training without loading. But you can get pumps on day 1.
Something like 100mcg Hup A are the ones I have. No, no amount of huperzine inhibiting breakdown is going to be or feel the same as an exogenous wave of surplus rolling over you available for sudden use. That would be like the difference in using testosterone enanthate routinely at any weekly dosage vs taking testosterone suspension specifically before training. Different feel, different cellular activities/acute gene expressions, different use cases.
I would not rely on injectable choline to raise my overall general choline levels; I can take citicholine for that and hup A. I take AlphaGPC acutely for training performance, or injectable specifically for very intense training. Not working out; training a motor pattern. Thinking burns choline, as does learning, lifting, all mental effort. If the raw substrate isn’t available in the brain, it will destroy existing structure for material to make the new connections. You want to be able to pay the learning/lifting toll up front.
Nothing about injections are inherently routine. You need to decide what is worth what effort to you. Everyone doesn’t need to inject choline to go do 60 minutes of machine screwoff training at their local Crunch fitness. If you are training for a competition for 4 months where all of your meals, sleep, and lifestyle are focused on improving the outcome of 1 day by even 2% for a plastic trophy, a 30-second slin pin injection a few times per week might easily be worth it to you.