Where We Are Today
Pheidi guides your workout intensity three ways, and all three ship today:
- VDOT pacing: exact pace ranges per mile/km, calculated from your race result or target time
- RPE (Rate of Perceived Exertion): a 1 to 10 effort scale with descriptions like "conversational pace" or "comfortably hard"
- Heart rate bands: a target bpm range on each eligible workout, built from your max heart rate
Heart rate is treated as a backup read on the same instruction rather than a separate prescription. One training zone maps to one bpm band, mirroring the pace band, so the pace target and the heart rate target can never disagree. It earns its place on the treadmill, in a tunnel, on trails where GPS wanders, and on hot days when pace stops meaning what it usually means.
What heart rate does in Pheidi today
- A prescribed band on each eligible workout. Shown on the day view, the week view, and over MCP, for VDOT runners and RPE runners alike.
- Max HR from Settings or onboarding, with an age-derived fallback of
207 - (0.7 x age)when you haven't measured one. With no max and no age on file, bands simply don't appear. - Karvonen bands when you add a resting HR. Percentages of your heart-rate reserve rather than of max, which individualises the band. Without a resting HR, bands fall back to a percentage of max.
- Logged heart rate, classified. Record an average HR with a run and the completed workout is labelled with the zone that average lands in ("148 bpm - Easy zone").
- No band for repetition work. Reps are too short for heart rate to reach steady state, so a target there would describe the rep you just finished rather than the one you're running.
Full detail: How Heart Rate Zones Work.
What heart rate does not do yet is drive anything. Bands annotate your plan; entering a max HR changes no distance, no workout type, and no rest day, and the logged zone label is a label rather than an input. Your weekly intensity distribution is tracked from logged effort and workout type, not from heart rate. Everything below is what turning heart rate into a signal Pheidi acts on would take.
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 to 75% | 1 to 4 | 75 to 90% | Conversational, relaxed breathing |
| Zone 2, Gray | 76 to 85% | 5 to 6 | 0 to 10% | Moderate, minimize this! |
| Zone 3, Hard | 86 to 100% | 7 to 10 | 10 to 25% | Tempo to all-out effort |
This maps cleanly to 5-zone models on watches: Garmin/Apple zones 1 to 2 = Easy, zone 3 = Gray (minimize), zones 4 to 5 = Hard.
Note: this is the research model for thinking about distribution, not the arithmetic behind the bands Pheidi prints on your workouts. Those come from your Daniels training zone (easy, marathon, tempo, interval), so their percentages don't line up one-for-one with the three zones above, and an easy run near the top of its band can sit inside this table's gray zone. See How Heart Rate Zones Work for the exact numbers.
The plan engine uses this model to structure your week, placing the right mix of easy runs, quality sessions, and rest days, and the heart rate band on each workout makes that structure visible while you're running it. What's still missing is the loop back: reading the heart rate you actually ran at and telling you how polarized your week really was.
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 to 95% | 0 to 5% | 5 to 15% |
| Build | 75 to 85% | 0 to 5% | 15 to 25% |
| Peak | 70 to 80% | 0 to 5% | 20 to 30% |
| Taper | 80 to 90% | 0 to 5% | 10 to 20% |
Notice the gray zone stays at 0 to 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 Shipped
Heart rate as a third intensity target alongside VDOT and RPE, with a bpm band built from your max HR on every workout that carries one.
What shipped
- Max HR in onboarding and Settings, measured or age-estimated (
207 - (0.7 x age)) - Optional resting HR, which switches the bands to the Karvonen heart-rate-reserve method
- A band on each workout in the day and week views, e.g. "130-150 bpm"
- Shown regardless of pacing preference, so pace, effort, and heart rate sit together
- Training zone drives the band: easy, long, medium-long and recovery runs share the easy band; race-pace, tempo and interval work each get their own; repetition work gets none
Phase 2, HR Tracking & Gray Zone Alerts Partly shipped
Logging heart rate and reading it back per workout is done. Turning a season of those readings into a picture of your intensity distribution is not.
What shipped
- An optional average heart rate field when you log a run, in the app and over the API
- Zone classification of that average on the completed workout ("148 bpm - Easy zone"), snapping to the nearest band and breaking ties toward the harder zone
- Server-side validation, so an implausible reading is dropped rather than stored or classified
What's still ahead
- Weekly intensity distribution computed from heart rate. Today's distribution tracking reads logged effort and workout type instead
- 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?
- Pace-versus-heart-rate drift as a fitness signal, distinct from the pace drift advisory that watches pace alone today
Phase 3, Wearable Integration & Adaptive Readiness Planned
Connect your watch or wearable to bring in HRV, resting heart rate, and sleep data automatically. Pheidi would combine this with your subjective feel to assess daily readiness and adjust your training accordingly. None of this is built yet.
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
Daily readiness would be 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 to 60 | Downgrade hard sessions to moderate |
| 60 to 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 to 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. Polarized distribution. Your feel matters most. The zone targets on each workout and the zone label on each logged run are live today; the analysis that reads a season of them, and the wearable readiness signals behind it, are still ahead. HR data arrives gradually so you're never overwhelmed, and VDOT and RPE stay first-class either way.
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 Heart Rate Zones Work The bands that ship today: where your max HR comes from, the Karvonen option, and how a logged heart rate is classified.
- 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.