Periodization
Your plan is divided into four training phases, each with a specific purpose. Phase allocation is based on total plan weeks:
| Phase | % of Plan | Min Weeks | Purpose |
|---|---|---|---|
| Base | 25% | 2 | Build aerobic foundation |
| Build | Remainder | — | Add intensity progressively |
| Peak | 15% | 1 | Race-specific work |
| Taper | 20% | 2 | Recovery before race day |
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.
By default a build or peak week carries one hard session. Your coaching style can raise that to two or three, and setting the count explicitly also reserves those days before the medium-long run — which is how a three-run week ends up as long / tempo / speed with no medium-long run at all.
A week never prescribes the same session twice. That makes the phase pool the real ceiling: a marathon peak week offers race pace and tempo and nothing else, so even a three-hard-day style gets two there. A slot the pool can't fill becomes an easy run rather than a repeat or a rest day. Hard days are also kept at least two days clear of the long run wherever the week has room, measured around the seven-day cycle so a Saturday session never lands next to a Sunday long run.
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 4 to 6 weeks of base building before the main plan. This starts at 1 mile per run and increases by 0.5 miles per week (metric plans: 2 km, adding 1 km 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 to 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.
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.