When bodybuilder came to us to buy T3 and T4, I was really a little confused. Can thyroid hormone help build muscle or build strength? What isThyroid Hormone Triiodothyronine T3? T3 stands for triiodothyronine, which is the physiologically active form of thyroid hormone. About 20 percent of T3 is secreted directly into the bloodstream by the thyroid gland, while the remaining …