Heart Rate Zones
Basecamp classifies training intensity with the Johnston 4-zone model. This page covers how the zones are defined, where their boundaries come from when you have no lab test, and what a lactate threshold test adds.
The Johnston 4-zone model
Two physiological markers define the zones:
- LT1 (AeT) — aerobic threshold heart rate
- LT2 (AnT) — anaerobic threshold heart rate
| Zone | Name | HR range | Purpose |
|---|---|---|---|
| Z1 | Recovery | Below AeT − 20 | Active recovery, very low stress |
| Z2 | Aerobic Base | AeT − 20 to AeT | Aerobic development, fat oxidation |
| Z3 | Tempo | AeT + 1 to AnT − 1 | Lactate tolerance, threshold work |
| Z4 | High Intensity | AnT and above | VO2max development, anaerobic capacity |
Every activity carrying heart-rate data gets a breakdown of time in each zone, so you can see whether a session built aerobic base, worked threshold, or went to the top end.
Where zone targets come from
Basecamp resolves zone targets from the best source it has, falling through when a source is absent:
| Priority | Source | What you get |
|---|---|---|
| 1 | Lactate threshold test | Measured HR zones and pace targets per zone |
| 2 | VDOT from best efforts | Estimated HR zones and estimated pace ranges, derived from your Strava race data |
| 3 | Garmin HR zone boundaries | Approximate HR zones, no pace targets |
| 4 | None of the above | Sessions prescribed by RPE (rating of perceived exertion) only |
Five-zone watch boundaries entered in Basecamp Settings are enough to start generating plans and reading zone distribution. As better data arrives, Basecamp moves up the list on its own.
The Garmin fallback
With no LT test and no VDOT, Basecamp approximates the Johnston boundaries from your Garmin 5-zone settings:
- LT1 ≈ the top of your Garmin Zone 2
- LT2 ≈ the top of your Garmin Zone 4
That produces usable heart-rate targets. Pace zones are unavailable in this mode, because there is no pace reference to derive them from.
What a lactate threshold test adds
An LT test is optional. Adding one enables the features that need measured thresholds rather than estimated ones:
- Pace targets per zone — each prescribed session gets a pace range as well as a heart-rate range
- Race time projections — finish time estimates from the Riegel formula and your LT2 pace
- Aerobic deficiency check — flags a narrow LT1-to-LT2 gap for review
- Lactate profile interpretation — places measured lactate values against population norms
- Mid-plan recalibration — a new test updates every future session target in an active plan, as one of the weekly refresh triggers
Without a test, these either fall back to VDOT estimates or are unavailable. Nothing else in Basecamp is gated behind it.
Aerobic deficiency (AeDS)
Aerobic deficiency describes an aerobic base that is underdeveloped relative to anaerobic capacity. Basecamp flags it when the gap between your aerobic (LT1) and anaerobic (LT2) heart rates is narrow, which means you reach threshold early in your effort range.
The check needs a lactate threshold test, because it compares 2 measured heart rates. It is a directional training signal, not a diagnosis.
Lactate profile interpretation
When a lactate threshold test includes measured blood-lactate values, Basecamp places them against population norms. Like the AeDS check, this needs an LT test, and the bands are context rather than a diagnosis — values move with protocol, fueling, fatigue, and test conditions.
Garmin zone mapping
Garmin devices report time in 5 heart-rate zones. Basecamp maps those onto the Johnston 4 zones by comparing each Garmin zone's midpoint against the Johnston boundaries. A Garmin zone straddling a boundary is split proportionally, so total training time is preserved.
Entering your zones
Enter your Garmin 5-zone boundaries under Basecamp Settings → HR Zones. That is enough for zone analysis and plan generation.
If you later take a lactate threshold test, add it under Basecamp Settings → Lactate Threshold. Basecamp switches to the measured zones from that point on.