How to set recurring days, but not the same days each week.

I have an interesting problem, but I'm sure others have had the same. I need to set my workout schedule for 3 days on, 1 off, 3 on, 1 off, etc. So it would be M,T,W, F,Sa,Su, T,W,Th, F,Sa,Su, etc. I'm sure there are people with work schedules with a similar issue. I need to have this on my calendar several months ahead so I can set up appointments, etc. The only way I can find to do this so far is to manually input every one, which is not only tedious, but extremely time consuming.
Does anyone know of a way to do this, or is there another calendar I could download which I could use which will allow this?