How Plan Generation Works

How Pheidi builds your personalized training plan from scratch.

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Periodization

Your plan is divided into four training phases, each with a specific purpose. Phase allocation is based on total plan weeks:

Shape-Based Distribution

Each week's workouts are distributed using a shape-based system. The long run anchors at 100%, and all other runs are expressed as a percentage of it. This guarantees a correct distance hierarchy where the long run is always the longest workout.

Quality Workout Selection

Quality workout types vary by phase and race distance. Available types include Tempo, Intervals, Hills, Fartlek, and Race Pace runs. The engine selects from a phase-appropriate pool to ensure progressive stimulus.

Taper Reduction

During taper, weekly volume is reduced progressively: Week 1: 75%, Week 2: 60%, Week 3+: 40% of peak volume.

Base Building (Beginners)

Complete beginners who aren't currently running get a 4–6 week base building phase before the main plan. This starts at 1 mile per run and increases by 0.5 miles per week, with a maximum of 3 runs per week.

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Research & evidence

Science behind this feature from pheidi.training.

• Running Training Plan: The Complete Guide Pillar hub linking 48+ deeper dives — start here for the full picture.
• Marathon Periodization: The Four Phases Base, Build, Peak, Taper — and what each phase actually does.
• Taper Science Bosquet et al.'s 41–60% volume-reduction sweet spot and 2.2% performance gain.
• Modern Marathon Plan Structure How elite plans actually allocate load across the cycle.
• Haugen Marathon Plan Study (2024) What 85 elite marathon plans reveal about training design.
• 92 Marathon Plans: What Differs Analysis of 92 published marathon plans and what they share.
• Percentage-Based Training Plans Why shape-based distribution beats fixed weekly templates.
• Pyramidal to Polarized Periodization How training distribution shifts as race day approaches.

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See also

• How Load Distribution Works How Pheidi shapes weekly distance around your long run using a shape-based system that keeps the hierarchy of run lengths consistent across the week.
• How Adaptive Progression Works How Pheidi increases your training volume safely: volume-aware increase rates, 3-up-1-down recovery weeks, and protection against rapid mileage spikes.
• How Plan Layers Work How Pheidi modifies your training plan non-destructively through overlay layers, so every change (vacation, injury, swap) can be undone without losing the original.