For two months I just did alernate strength/aerobics days
Dania:
I certainly am not an expert at pre-STS rotations, since I just completed my first STS week last week. So I invite more experienced STS'ers to answer your question as well.
But I prepared for STS for about two months, in May and June. And what I decided to do was to mimic what STS would be like, by doing 3 strength videos on T/Th/Sat, and three aerobics videos on M/W/F . For the strength videos, I stuck with Cathe videos: mostly the two pyramid, S&H and PS ones -- but also Power Hour and Maximum Intensity: Strentgh. For the aerobics days, I did easy stepping, but also some intense boot camp and kickboxing type videos. All my sessions lasted slightly over an hour.
I calculated my 1RM's early, in early May, and did three or four STS's early in April just out of interest. I found that the STS's blew me away, so that's why I trained for two months. As for my first week of STS, I found that I was able to cope with the Discs I,2,3 -- nearly making through al three of them, but it was tough. So tough, I did two days (Wednesday and Friday) of fairly easy aerobics. Yesterday (Saturday) I did disc 3 ("legs"), and it was so tough, I plan on taking it easy today. When I get off of this forum page I am going to do some very easy step aerobics and some extra stretching for about 50 minutes. Mondays I take off.
On thing I found out is that my 1RMs increased over the two months, so I have had to continually uipdate them.
There is plenty discussion on various Cathe forum pages about what to do on the "off" aerobics days with STS. I think more and more I will just do easy, relaxing aerobics using various videos here and there, and extra stretching -- to prepare for the hard STS days. The STS discs are very challenging, and I respect their toughness and the people who try them out.
These are my thoughts to your question. Like I said, I am just starting and would like others' views on this.
-- David