📖 How to Use PTH ZoneForge
▼Profile & Thresholds
Enter the athlete's weekly hours, training age, client category (1–6), and heart rate / power thresholds at LT1 and LT2.
Recommendation
Review the automatically generated zone distribution, intensity protocols, and — once dates are set — the full periodisation block timeline with per-week prescriptions. Download the Excel template.
Upload & Review
After each week (or training cycle), upload the filled Excel log. PTH ZoneForge parses zone minutes, sRPE, HRV, sleep, and readiness scores, then proposes evidence-based plan adjustments.
Daily Readiness
Use every morning before your session. Click the Daily Readiness tab, answer 5 quick sliders (sleep, fatigue, mood, soreness, motivation) and get an instant session prescription — whether to train normally, reduce intensity, or take the day off. No upload needed; just answer and scroll to the output.
Tips: Start with an accurate LT1 HR (60-min steady-state effort, average HR last 20 min) — everything else scales from there. Re-test thresholds every 8–12 weeks or at the end of a Realization block. Client categories 1–2 (competitive athletes) tolerate 4-week loading blocks; categories 5–6 (frail / rehabilitation) should use 2-week blocks with conservative ramp rates. All recommendations follow polarised / pyramidal distribution principles (Seiler & Tønnessen, 2009; Muñoz et al., 2014).
Step 4 — when to open it: Click the Daily Readiness tab on any day you plan to train, in the morning before starting. Answer the 5 wellness sliders (sleep quality, fatigue, muscle soreness, mood, motivation) and PTH ZoneForge immediately recalculates your zone targets for that day. A green output means train as planned; amber means reduce intensity; red means rest or easy movement only. You can use it standalone — you do not need to go through Steps 1–3 first every time.
🔬 Why 3 Zones? — Understanding the Model
▼The short answer
PTH ZoneForge uses a 3-zone model anchored at two physiological thresholds — LT1 (your aerobic threshold, where lactate begins to accumulate) and LT2 (your anaerobic threshold, where lactate accumulation becomes maximal). This is not a simplification — it is the model most consistent with exercise physiology and the one used in the majority of high-quality endurance research (Seiler & Kjerland, 2006; Lucia et al., 2000; Stöggl & Sperlich, 2014).
Most coaches and athletes are familiar with 5-zone or 7-zone models from devices such as Garmin, Polar, TrainingPeaks, or Coggan's power model for cycling. These models are not wrong — they subdivide the same physiology with finer resolution. The 3-zone model simply names the three qualitatively different metabolic states that actually exist, without artificial subdivisions that devices invent for display purposes.
The three metabolic states
- Zone 1 — below LT1. Fully aerobic, fat-dominant, fully recoverable.
- Zone 2 — LT1 to LT2. "Grey zone" — harder than easy, not hard enough. Avoid unless prescribed.
- Zone 3 — above LT2. High-intensity. Short, structured intervals only.
- Zone 1 → our Zone 1 (recovery)
- Zone 2 → still our Zone 1 (aerobic base)
- Zone 3 → our Zone 2 (grey zone)
- Zone 4 → lower Zone 3 (threshold)
- Zone 5 → upper Zone 3 (VO2max / supramaximal)
- Z1 Active recovery → our Z1
- Z2 Endurance → our Z1
- Z3 Tempo → our Z2
- Z4 Threshold → lower Z3
- Z5 VO2max → mid Z3
- Z6–Z7 Anaerobic / NM → upper Z3
How to map your device's zones to PTH ZoneForge
If your GPS watch, power meter, or training platform shows you zones 1–5 or 1–7, use this table to translate before entering data into ZoneForge or logging in the Excel template. The key anchors are always LT1 and LT2 — everything else is just subdivision.
| PTH ZoneForge | 5-Zone (HR %max) | Coggan 7-Zone (% FTP) | Physiological marker | Real-time feel |
|---|---|---|---|---|
| Zone 1 | Z1 + Z2 (<75% HRmax) | Z1 + Z2 (<75% FTP) | Below LT1 — lactate stable, fat-dominant | Can sing effortlessly. Full sentences. Could run for hours. |
| Zone 2 | Z3 (75–85% HRmax) | Z3 Tempo (76–90% FTP) | LT1→LT2 — lactate rising, no equilibrium | Singing gets strained. Sentences get shorter. Breathing noticeable. |
| Zone 3 | Z4 + Z5 (>85% HRmax) | Z4–Z7 (>91% FTP) | Above LT2 — maximal lactate, VO2max territory | Speaking only in words. Breathing maximal. 3–8 min intervals maximum. |
Why not use 5 or 7 zones in ZoneForge?
Distribution research uses 3 zones. The evidence for polarized training (≈80% low / ≈10% high / ≈10% threshold-grey) is built on the 3-zone framework. Translating to 5 or 7 zones loses the clarity of what matters: how much time is truly below LT1, and how much is truly high intensity above LT2.
The "grey zone" problem. Devices that show Z3 of 5 as "tempo" encourage athletes to train there regularly. The physiology shows this is the least productive zone for most endurance athletes — too hard to allow full recovery, not hard enough to drive the same adaptations as Zone 3 intervals. By calling it Zone 2 explicitly and prescribing very little of it, ZoneForge keeps you out of the trap that derails most self-coached athletes.
LT1 and LT2 are the real anchors. Enter your thresholds accurately in Step 1 — the rest of the model builds from those two numbers. Any 5-zone or 7-zone system that is properly calibrated to your thresholds maps cleanly onto the 3-zone model above.
References: Seiler & Kjerland (2006) Scand J Med Sci Sports; Lucia et al. (2000) Med Sci Sports Exerc; Stöggl & Sperlich (2014) Front Physiol; Muñoz et al. (2014) Int J Sports Physiol Perform.
Upload a recent steady Zone 1 session (60+ min, power held at LT1, no intervals)
as a .tcx file exported from Garmin Connect, Wahoo, or Strava. The tool calculates
aerobic decoupling (Pw:HR) to verify whether the aerobic base is ready for the prescribed
distribution — especially before recommending threshold or Zone 3 sessions.
Export from Garmin Connect: Activity → ⋮ → Export to TCX | Wahoo: Export → TCX |
Strava: Activity → ⋮ → Export GPX (GPX contains HR+power; select TCX if available)
Select up to two protocols matching your training phase and category. The distribution explainer above shows the recommended balance of threshold vs Zone 3 sessions. Use the type filters to find the right protocols. Evidence base: Seiler (2013), Rønnestad (2015, 2020), Billat (2000), Norwegian Method (Casado et al. 2023).
Watts and HR from your lactate test are the primary anchors. These evidence-based cues let athletes self-monitor in real time. They are also a coaching tool — ask your client these questions mid-session.
The popular rule "you should be able to talk but not sing" is often misinterpreted as describing the middle of Zone 1. The research shows this is wrong. "Can talk, cannot sing" marks the ceiling of Zone 1 — you are crossing LT1, not safely inside it.
A controlled cycling study (Dehart-Beverly et al. 2000; confirmed by Talk Test vs. LT cycling study, ResearchGate 2021) found that the power and heart rate at LT1 were significantly lower than the "last positive" Talk Test stage (still speaking comfortably). You can already be above LT1 and still speak comfortably for a while. Losing the ability to sing is the signal that you have already crossed LT1. For Zone 1 training, singing should remain effortless. The moment it becomes difficult, slow down.
Controlled cycling study (n=13, incremental test, Talk Test vs. direct lactate measurement): LT1 power (88±22 W) and HR (115±15 bpm) were significantly lower than the "last positive" Talk Test stage (127±26 W). You can already be above LT1 and still talk comfortably. The singing cue disappears first — it is the earliest signal of LT1 being crossed. (ResearchGate 2021)
Landmark University of Wisconsin study: as long as subjects answered "yes" to "can you speak comfortably?", they were below VT1. At the first equivocal answer ("yes, but…"), they were right at VT1. The flat "no" stage corresponded to VT2 (respiratory compensation threshold). Three TT stages map cleanly to three training zones.
Multiple sources (ACE 2025; exercise physiology textbooks; Brainly/VT1 consensus): "At VT1, a person should be able to maintain a conversation with some effort but not be able to sing." This is a marker of crossing LT1, not of comfortable Zone 1 training. Practical implication: for Zone 1, singing must remain effortless, not merely possible.
San Millán's practical cues for LT1/Zone 2 boundary: full sentences still possible, but phone caller hears the effort. Inability to sing signals LT1 crossed. Breathing below LT1 should feel similar to walking — barely elevated. High North Performance (2023): "If breathing is as easy as at rest, you are likely in Zone 1. If you are having to take breaths at unnatural points mid-sentence, you are in Zone 3."
Three evidence-based phenomena tell you in real time whether your Zone 1 session is drifting above LT1 — even when your power or pace feels constant. Understanding all three helps you decide whether to reduce intensity, reduce duration, or accept the drift based on its cause.
What happens: During prolonged exercise at a fixed wattage or pace, HR rises progressively even though workload is unchanged. This is called cardiovascular drift or cardiac drift. Stroke volume falls (less blood per beat) so the heart beats faster to maintain cardiac output. The main drivers are rising core temperature and dehydration reducing plasma volume — roughly half of cardiovascular drift is attributable to dehydration; the other half to hyperthermia and its cardiovascular effects.
San Millán's hydration rule: He advises that with good hydration, HR drift during a Zone 1/2 session should be no more than 4–6 bpm above the starting value. Drift beyond this is primarily a dehydration or heat signal — not a fitness problem (High North Performance, 2023; San Millán / Attia podcast).
TrainingPeaks decoupling metric (Pa:Hr) — the same principle calculated as power-to-HR ratio across the two halves of a session. <5% decoupling = aerobically efficient; >5% = intensity was above pure aerobic threshold (Friel; TrainingPeaks).
What happens: The mirror image of phenomenon 1. If you train by HR ceiling (e.g. "stay below LT1 HR"), your body compensates for rising internal demand by reducing power output — you naturally slow down or lower watts to stay within the HR cap. This progressive power decay is a valid biomarker that the session has exceeded aerobic steady state.
Research on subjects exercising at HR slightly above the gas exchange threshold (VT1) showed that work rate must decrease over time to maintain that HR — the body is working harder than the aerobic system can comfortably sustain.
Practical rule (Uphill Athlete / Friel): Track Efficiency Factor (EF = Normalized Power / Avg HR) over time. A rising EF at the same HR means LT1 fitness is improving — a useful longitudinal marker alongside lactate retesting every 8–12 weeks.
What it is: A non-linear HRV index (Detrended Fluctuation Analysis, short-term scaling exponent α1) that tracks the fractal correlation properties of heartbeat patterns during exercise. As intensity increases, DFA α1 falls from ~1.0 (rest) through a predictable range. When DFA α1 drops to approximately 0.75 during an incremental exercise test, this corresponds to VT1/LT1 — the HRV threshold (HRVT). Below 0.75 = Zone 1; above 0.75 = you have crossed LT1.
Validation (Rogers et al. 2022 — elite triathletes): Near-perfect correlation between LT1 power and HRVT1 power (r = .98), with minimal bias (−5.3 ± 10.4 W). HR correlation was also strong (r = .77).
Key advantage: Unlike HR drift or talk test cues, DFA α1 is not confounded by dehydration, heat, or fatigue — it reflects the current metabolic demand regardless of environmental conditions. Zone boundaries also shift with altitude, illness, or overreaching, and DFA α1 captures these shifts automatically.
How to use it in practice: Requires a chest strap that records RR intervals (Polar H10 recommended). Apps: HRV Logger (iOS/Android, free), AI Endurance, Runalyze. Watch DFA α1 in real time — the moment it approaches 0.75 during a Zone 1 session, you have reached your LT1. Reduce pace/power to restore α1 above 0.75.
Plan your macrocycle structure based on traditional periodisation — high volume early, increasing intensity and specificity toward competition. Blocks auto-adapt to your client category and current training phase.
No upload required — just answer the questions below and scroll to your session prescription.
Answer the sliders below (or upload a completed daily-log Excel file) and get an instant output — a full re-prescription of today's session with specific power / HR adjustments and a recovery recommendation. Missing fields are ignored gracefully; even 2–3 answers generate a meaningful adaptation.
Answer the sliders below and get instant output.
Download the template, fill in each morning, upload mid-week for the same output.