Hi, Paul.
I think it's very possible that your methylation cycle was being overdriven. I've seen this in several others now, based on lab tests, when they were taking sizeable dosages of methylfolate together with so-called "active" forms of B12. This combination bypasses the ability of the cells to control the rate of the methionine synthase reaction. It goes too high, using up too much homocysteine, and then there is not enough homocysteine left to enter the transsulfuration pathway to support the synthesis of glutathione. The glutathione depletion worsens, and the oxidative stress increases. One major effect of this is to worsen the mitochondrial dysfunction, lowering the production of ATP. Since ATP is what is needed to power the muscles, they get weak. So this approach does improve methylation, but it does so at the expense of glutathione. What is needed is a more balanced approach, in my opinion. This is one reason I suggest using hydroxocobalamin, at least at first, instead of methylcobalamin. That will preserve the supply of homocysteine to support glutathione synthesis. This does not work for everyone, and if it doesn't, I suggest switching to methylcobalamin, but limiting the dosage to about 2 milligrams per day, and limiting the methylfolate dosage to a few hundred micrograms. Starting at low dosages and working up as tolerated is a good idea, in my opinion.
Best regards,
Rich