Hi, I bought the base plan, as I'm just too busy to not have a handy plan in place.  One question, please.  (I'm 52.5 and just switched back to xc from dh last year, with success.) 

I believe the plan is based on 4-week cycles.  Shouldn't I be doing 3-week cycles at my age, rest every 3rd?  If so, do you have an adjustment to your base plan using a 3-week cycle, instead, already available?  If you don't have the plan on a 3-week cycle but suggest that I do switch to that, do you have any advice?  How do I still get the most out of the plan if I have to drop the 3rd week?