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 25 miles per week to 45 miles per week. Aerobic development builds from 40 miles per week to 50 miles per week. Race-Specific Introduction phase maintains at 50 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 ...