Methodology

Pacer creates weekly training plans based on your personal performance data, physiological thresholds and race goals. This page explains how it works — from data sources to the finished training session.

1. Data Sources

Pacer draws information from three sources:

  • Strava — your training history from the last 90 days. From pace, heart rate and session structure, Pacer estimates your current performance thresholds (LT1 and LT2). Activity names and descriptions are stripped before processing.
  • Garmin Health API — HRV, Body Battery, sleep quality and daily measurements. These signals feed exclusively into local load constraints (e.g. maximum quality sessions per week) and are never transmitted to external services.
  • Your profile — manually entered values such as lactate test results, HRmax, VO₂max, rest days, peak volume and race goals always take precedence over automatically estimated values.

2. Threshold Determination

Core to the planning are two physiological thresholds:

  • LT2 (lactate threshold 2) — the anaerobic threshold, the fastest sustainable pace over ~30–60 minutes. It is estimated from your race times or the typical pace of your hard runs, roughly equivalent to your 10k race pace.
  • LT1 (aerobic threshold) — the pace below which you burn almost exclusively fat and recover quickly. Pacer determines LT1 statistically from your easy runs of the last 90 days — either via heart rate drift (when HR data is available) or via the distribution of your running paces.

If you have completed a lactate test, your measured values override all estimates. Garmin VO₂max values are used as a supplementary reference but do not replace a test.

3. Training Zones

From LT2 (and optionally LT1), Pacer derives a five-zone system:

  • Zone 1 — Recovery, well below LT1
  • Zone 2 — Aerobic base range, below LT1
  • Zone 3 — Tempo between LT1 and LT2 ("grey zone")
  • Zone 4 — Threshold pace, around LT2
  • Zone 5 — VO₂max range, above LT2

Each zone is defined as a pace range (min/km) and, if available, a heart rate range (bpm). Zones can be adjusted manually in your profile.

4. Load Management

Pacer follows a polarised training approach: the majority of volume sits in zones 1–2, a small portion (quality sessions) in zones 4–5. Zone 3 is used sparingly by design.

Weekly volume is based on your current 8-week average from Strava and increases in a controlled manner — typically no more than 10% per week. Garmin recovery signals can reduce the planned volume in a given week if your recovery is insufficient.

The number of quality sessions (intervals, threshold runs, tempo runs) per week is capped at two and depends on your training phase and recovery.

5. AI-Powered Planning

Based on all of the above, Pacer generates a structured plan each week. The AI (Claude by Anthropic) receives:

  • Your athlete profile (goals, training history, thresholds, zones)
  • The current training week and phase (build, peak, taper, recovery)
  • Derived load constraints from Garmin signals — no raw data
  • Your rest days, preferences and any optional coach notes

Strava activity names and descriptions are deliberately filtered out before data is sent to the AI. Garmin raw data (HRV values, Body Battery, stress scores) never leaves the server.

The generated plan contains a clear session for each training day with a target zone, distance and specific pace targets. For long runs and interval sessions, the structure and purpose of the session are explained.

6. Periodisation and Race Preparation

Pacer structures training in phases:

  • Build — Gradual increase in volume and intensity over several weeks
  • Peak — Highest volume and maximum quality work shortly before the taper
  • Taper — Targeted load reduction in the 2–3 weeks before your A-race to arrive fresh at the start line
  • Recovery — Low load after races before the next build begins

If you have B- or C-races in the calendar, these are taken into account during the build: volume is slightly reduced in the weeks before, then quickly rebuilt afterwards.

7. Manual Review

Every plan goes through a manual review before delivery. Only after approval is the plan sent by email and optionally via Telegram. If something is off — such as pace zones or session structure — the plan can be rejected and regenerated with a correction note.

Privacy

All data flows — in particular which information is transmitted to external services (Strava API, Garmin Health API, Claude API) — are documented in the Privacy Policy. Processing of Strava data is carried out only with your explicit consent (GDPR Art. 6(1)(a)).