Pathways can be tricky, hacking is the way to go. By this I mean you have to find the missing link. I usually start with the vitamin co-factors then specific minerals and by specific aminos. I would look at the other b vitamins since tipping the scale with specific ones (folate, B12) can cause suppression of the other b vits.
Everyone is individual so you never know what you get but I like B2 and B6 but never neglect the others. Muscle loss is usually a catabolic reaction where the body is using the proteins from muscle to keep the machine going. There is a pathway called the alanine cycle that explains this, but this may not explain it either.