Run Pace Architect

Overview

Most runners train in the wrong zone: their "easy" runs are too fast (so their hard days can't be hard enough) and their hard days are too slow (because they are always tired). The fix is a pace table generated from one honest recent race performance — not from a wish, not from a single good interval session.

This skill is that table generator plus the planning math around it:

1. Equivalent performances — Riegel's power-law model (T2 = T1 × (D2/D1)^1.06) converts one race result into predicted times for every common distance.
2. Training zones — easy, long-run, marathon, threshold (defined precisely as the pace you could hold for 60 minutes, solved numerically), interval (VO₂max) and repetition (speed) paces, each derived from the same model.
3. Goal feasibility — is a 22:30 → 21:00 5K in 8 weeks realistic? The tool compares the required improvement against typical per-block gains for trained vs novice runners and says LIKELY / AGGRESSIVE / UNREALISTIC.
4. Mileage ramping — 10%-per-week cap with an automatic down week every 4th week, simulated week by week until the target mileage is reached.
5. Race-day splits — even-split tables (per-km and per-mile) for a goal time.

When to Use

• "I ran a 5K in X — what should my training paces be?"
• "What marathon time does my 10K predict?"
• "Is my goal of sub-1:45 half realistic in N weeks?"
• "I run 25 km/week, I want to get to 50 — how fast can I ramp?"
• "What pace per km do I need for a sub-X race?" → split tables
• Pacing a training plan: which phase (base / build / peak / taper) to run

Don't use for: injury diagnosis, shoe selection, trail/ultra pacing over wildly varying terrain (Riegel assumes even, road-like conditions), or heart-rate zone calculation without field data.

Quick Start

# All training paces from a recent 5K
python3 scripts/run_pace.py zones --race 5k=22:30

# Equivalent race predictions from one performance
python3 scripts/run_pace.py predict --race 10k=48:00 --to hm,marathon

# Feasibility of a goal + phase structure for the block
python3 scripts/run_pace.py plan --race 5k=22:30 --goal 5k=21:00 --weeks 8

# Safe mileage ramp with cutback weeks
python3 scripts/run_pace.py ramp --current 30 --target 50

# Race-day split table
python3 scripts/run_pace.py splits --race hm --goal 1:45

# Everything in miles
python3 scripts/run_pace.py zones --race 5k=22:30 --unit mi

How the Math Works

Riegel equivalent performances

Riegel (1981) modeled distance-running time as a power law:

T2 = T1 × (D2 / D1)^1.06

A 22:30 5K therefore predicts a ~47:00 10K, a ~1:44 half and a ~3:38 marathon. The exponent 1.06 is the classic road-running value; it assumes even pace, comparable terrain and adequate training for the target distance. Predictions degrade when you jump more than ~4× in distance (a 5K predicts a marathon poorly for an untrained runner).

Training paces (all derived from the same model)

The threshold pace is solved, not guessed: the script binary-searches the distance D where your predicted time equals exactly 60 minutes, then reports that pace. That is the textbook definition of threshold (one-hour race pace).

Feasibility of a goal block

Required improvement = (current − goal) / current. Rules of thumb encoded:

• Trained runners: 1–3 % per 8–12 week focused block is realistic.
• Novice/returning runners: up to 5–8 % is possible (bigger fitness headroom).
• More than that in one block → verdict AGGRESSIVE (extend weeks) or UNREALISTIC (split into two blocks with a race in between).

Block structure output for N weeks: base (~50% of weeks, volume + easy strength), build (~30%, key sessions get race-specific), peak (~20% minus taper, sharpening), taper (final week: −30–40% volume, intensity kept). Every phase lists its purpose and the key session shape.

Mileage ramp safety

• Never increase weekly volume more than 10 % week-over-week.
• Insert a cutback week (−20 %) every 4th week — adaptation happens during recovery, not during accumulation.
• The tool simulates this rule week by week and prints the schedule, including how many weeks the ramp actually needs (usually more than people expect).

Common Pitfalls

1. Feeding it a training-run time. Garbage in, garbage out. Use a real race or an all-out time trial on a measured course, in race conditions.
2. Easy pace creep. If easy pace feels "too slow", that's correct — elite runners do the majority of volume slower than marathon pace.
3. Trusting a 5K → marathon prediction without marathon training. The model assumes you can actually cover the distance; the prediction is "with appropriate training", not "tomorrow".
4. Ramping volume and intensity simultaneously. The 10 % rule applies to volume; add quality only after volume has been stable for 2–3 weeks.
5. Even splits ≠ negative splits. The split table assumes even pacing; going out 10 s/km faster than plan is the classic marathon blow-up recipe.

Verification Checklist

• Input race time parses (5k=22:30, 10k=48:00, marathon=3:15:00)
• Zones table prints all five zones in per-km AND per-mile
• Threshold pace sits between marathon pace and interval pace
• Feasibility verdict matches required-% vs the 1–3 % / 5–8 % bands
• Ramp table includes a −20 % cutback every 4th week and never exceeds +10 %
• Splits table sums exactly to the goal time

Examples

$ python3 scripts/run_pace.py zones --race 5k=22:30
Reference performance: 5K in 22:30 (4:30/km)
  Easy          5:26–5:56 /km   (8:45–9:33 /mi)
  Long run      5:41–5:56 /km
  Marathon      4:50 /km        (predicts 3:24:30)
  Threshold     4:40 /km        (your 60-minute pace)
  Interval      4:22 /km        (3K–5K effort)
  Repetition    4:04 /km        (1500 m effort)

$ python3 scripts/run_pace.py plan --race 5k=22:30 --goal 5k=21:00 --weeks 8
Required improvement: 5.6% in 8 weeks → AGGRESSIVE for a trained runner
(likely OK for a novice; consider 10-12 weeks)
  W1-4  BASE    volume +, strides 2×/wk
  W5-6  BUILD   VO₂max intervals + threshold
  W7    PEAK    race-pace specific
  W8    TAPER   −35% volume, keep strides

Data and formulas: Riegel fatigue model; threshold-as-one-hour-pace convention; widely used 10 %-rule and 4th-week-cutback practice. Individual response varies — the numbers are starting points, not prescriptions.