I'm finishing up the Pfitz 18/70 plan and am beginning to have some minor doubts about the plan's lack of workouts run at marathon pace. For those unfamiliar, in recent weeks the plan had called for a mix of weekly workouts: one interval/Vo2 max session, one medium long run of 13-15 miles, one long run of 18-20 miles, and the balance easy runs with strides mixed in. The only workouts that specifically target marathon pace are the two "fast finish" long runs over the course of the plan. While I have nailed these workouts, I was fairly spent afterwards. Overall I feel like most of my runs have been done either slower or faster than MP. Has anyone experimented with turning either there medium long run or other weekly mileage into a MP run? I typically have run a 35-40 tempo at around 95% of half marathon pace once per week because I felt the plan lacked intensity.