Sonya, I doubt you would lose muscle doing STS. You could work them in a different order. I would think you were getting endurance with your plyo days for legs. Maybe you could just do Meso 2 and 3 then see how you feel about starting 1. I think when I am through with Meso 3 I am going to go back and do Meso 1 but do plyo legs on leg days. You would probably start out stronger after what you have been doing and build from there with STS.