12 Week Marathon Training Plan This plan is built for an experienced runner who can handle 75-90 miles per week. This plan incorporates 6 days of running a week with 3-4 singles and 2-3 doubles with one day off a week. This runner is likely very experienced and very competitive and prepared to take on a significant training load. This plan is designed to be 12 weeks of marathon specific training, it is advised to start this plan coming off of an aerobic development, 5K, 10K, or half marathon ...