I have a question about periodization in regards to marathon / half marathon training. I am recently returning to training after about 2.5 years off and I am shooting for a half some time in May. I have been building my mileage up over the past two months and will max out at 70 miles a week some time this month. For the last two weeks, I have been incorporating a mix of Marathon pace (during long runs), Half Marathon pace and Temp paced runs throughout my training week. I am also planning on incorporating interval miles into this program starting in Feb.
My question is: how long can expect to keep improving with this almost exclusive focus on Tempo/ threshold runs? Providing a keep adjusting my paces as my fitness increases, will a well rounded schedule keep me from getting stale or plateauing or do I need to rework my schedule? Should I focus on longer/slower tempo runs in the beginning and then transition to faster tempo/interval paces as I get closer to the race or should I delay the onset of workouts entirely until I have a more established base. I am more interested in a risk adverse approach to training because I am sick of being injured and overtraining. To give a little background I ran in college and spent two years at 90/110 miles per week. I’m looking to run under 1:15 come May. Any advice would be appreciated.