12 Week Winter Running Plan Base phase: 3-4 weeks Aerobic Development phase: 5-6 weeks Race-Specific Introduction phase: 3 weeks Base phase builds from 35 miles per week to 65 miles per week. Aerobic development builds from 55 miles per week to 75 miles per week. Race-Specific Introduction phase maintains at 75 miles per week. Down weeks built into training schedule. This plan is built for a very experienced (3+ years of running experience) runner looking to prepare themselves for the ...