Where We Are Today
Pheidi currently supports two ways to guide your workout intensity:
- VDOT pacing — exact pace ranges per mile/km, calculated from your race result or target time
- RPE (Rate of Perceived Exertion) — a 1–10 effort scale with descriptions like "conversational pace" or "comfortably hard"
Both work well, but many runners — especially those with GPS watches — think in heart rate. Heart rate zones are a natural third option that bridges the gap between objective pace data and subjective effort feel.
The Polarized Training Foundation
Pheidi's plan engine already enforces a polarized training distribution based on Dr. Stephen Seiler's research and multiple meta-analyses. The principle: approximately 80% of your training volume should be easy, with only 20% at hard intensity. Minimal time should be spent in the "gray zone" — too hard for recovery, too easy for speed gains.
3-Zone Polarized Model
| Zone | HR (% of Max) | RPE | Target Volume | Feel |
|---|---|---|---|---|
| Zone 1 — Easy | 0–75% | 1–4 | 75–90% | Conversational, relaxed breathing |
| Zone 2 — Gray | 76–85% | 5–6 | 0–10% | Moderate — minimize this! |
| Zone 3 — Hard | 86–100% | 7–10 | 10–25% | Tempo to all-out effort |
This maps cleanly to 5-zone models on watches: Garmin/Apple zones 1–2 = Easy, zone 3 = Gray (minimize), zones 4–5 = Hard.
Today the plan engine uses this model to structure your week — placing the right mix of easy runs, quality sessions, and rest days. Heart rate zones will make this visible on each workout.
Intensity Targets by Training Phase
The optimal intensity distribution shifts as you progress through your plan. Early phases are more aerobic; later phases allow more hard work as your fitness builds.
| Phase | Easy (Zone 1) | Gray (Zone 2) | Hard (Zone 3) |
|---|---|---|---|
| Base | 85–95% | 0–5% | 5–15% |
| Build | 75–85% | 0–5% | 15–25% |
| Peak | 70–80% | 0–5% | 20–30% |
| Taper | 80–90% | 0–5% | 10–20% |
Notice the gray zone stays at 0–5% across all phases. That's intentional. The most common training mistake is spending too much time at moderate intensity.
Roadmap
Phase 1 — HR Zone Display
Add heart rate zones as a third pacing option alongside VDOT and RPE. Each workout card will show a target heart rate range based on your max HR.
What this looks like
- New profile option: enter your max heart rate (manual or age-estimated)
- Each workout shows its HR target — e.g., "Easy run: keep HR below 150 bpm"
- VDOT, RPE, and HR can complement each other — see pace, effort, and heart rate together
- Workout type maps to HR zone: easy/long/recovery runs → Zone 1, tempo → upper Zone 2/lower Zone 3, intervals → Zone 3
Phase 2 — HR Tracking & Gray Zone Alerts
After workouts, log your actual average heart rate. Pheidi will analyze your intensity distribution across the week and flag gray zone creep — the most common training mistake for recreational runners.
What this looks like
- Post-workout: optional field for average HR and max HR
- Weekly intensity distribution chart — see how much time you spent in each zone
- Gray zone alerts: "Your Tuesday easy run averaged 82% max HR — that's gray zone. Try slowing down to keep it under 75%."
- Trend tracking over weeks — are you getting more polarized or drifting toward the middle?
Phase 3 — Wearable Integration & Adaptive Readiness
Connect your watch or wearable to bring in HRV, resting heart rate, and sleep data automatically. Pheidi combines this with your subjective feel to assess daily readiness and adjust your training accordingly.
Supported platforms (planned)
| Platform | Data |
|---|---|
| Garmin | Body Battery, HRV Status, Sleep Score, Resting HR |
| Apple Watch | HRV (rMSSD via HealthKit), Resting HR, Sleep Duration |
| Whoop | Recovery Score, HRV, Sleep Performance |
| Oura | Readiness Score, HRV, Sleep Score, Resting HR |
| Polar | Nightly Recharge, HRV, Sleep Score |
Composite readiness score
Your daily readiness is a weighted blend of subjective feel and wearable data:
| Signal | Weight |
|---|---|
| Your subjective rating (how you feel) | 40% |
| HRV trend | 25% |
| Sleep quality | 20% |
| Resting HR trend | 15% |
Override rule: If you feel tired or exhausted (subjective ≤ 2), Pheidi always downgrades regardless of wearable data. Your feel matters more than numbers.
How readiness adjusts your plan
| Readiness Score | Adjustment |
|---|---|
| Below 40 | Suggest rest day or easy walk |
| 40–60 | Downgrade hard sessions to moderate |
| 60–80 | Proceed as planned |
| Above 80 | Optional stretch goal offered (never pushed) |
Design Principles for HR Features
Heart rate data is powerful but easy to misuse. These principles guide how Pheidi will integrate it:
- Subjective feel always wins. Wearable data supplements your judgment — it never overrides it. If you feel terrible but your HRV looks great, we trust you.
- Trends over snapshots. A single bad HRV reading means nothing. Pheidi shows trend arrows (↑ ↓ →) rather than raw numbers to avoid data anxiety.
- Learning period before auto-adjustments. Wearable data needs 7–14 days of baseline before it's useful. During this period, Pheidi shows data but doesn't act on it.
- Simple zones, not data overload. Three zones (easy, gray, hard) are enough. We won't drown you in five-zone breakdowns and VO2max estimates.
- Always optional. HR features enhance the experience — they're never required. VDOT and RPE remain first-class pacing options.
Key Takeaway
Heart rate training in Pheidi follows the same philosophy as everything else: clarity over complexity. Three zones. Polarized distribution. Your feel matters most. We'll add HR data gradually — starting with simple zone targets on each workout, then post-run analysis, then wearable integration — so you're never overwhelmed.
The web app is live today — sign in to build a plan.
Research & evidence
Science behind this feature from pheidi.training.
- Polarized Training: The Gray Zone Problem Why most runners train too hard on easy days and too easy on hard days.
- Individualized Training Zones (2025) Why fixed heart rate zones fail and what replaces them.
- The 80/20 Polarized Training Rule Dr. Stephen Seiler's session-count distribution across elite endurance sports.
- The Gray Zone Training Mistake Zone 2 costs fatigue without the adaptations of Zone 3.
- Wearables and Biofeedback for Injury Prevention Readiness metrics, recovery scores, and what they predict.
See also
- Mobile App and Health Integration Roadmap A future native iOS and Android app that will sync your training with Apple Health and Google Fit, with offline plan access and live workout guidance.
- How Pacing Guidance Works How Pheidi calculates your training paces: VDOT pace zones, Borg RPE descriptions, and heart rate alternatives for every workout type.
- 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.