A lot of what causes muscle loss is diet. Sure a high dose of T3 would more rapidly break muscle down, but you should be just fine on your HRT dosing. Remember though, muscle is not lost over night. I have my cleints take pics regularly. We watch their progress. We make sure that fill out as often as needed to keep muscle full and round. If you are watching yourself close and adding in refeed days when you go flat for an extended period, you will be able to stop must of the potential muscle loss.