I wouldn't do cardio 6 days a week along with STS. I think that is too much. Your body is probably telling you it's tired. I do 3 days a week of cardio when I did my STS rotation. I pretty much listen to my body and if I don't feel up to it, I don't do the cardio, or shorten it. I was able to pretty much keep to Cathe's rotation, though.