Training Effect
Every activity in Basecamp gets 2 modeled scores on a 0–5 scale: aerobic and anaerobic Training Effect. They estimate how much the session stressed each energy system. This page covers what the scores mean, what moves them, and how accurate they are.
What the scores mean
| Score | Label | What it tells you |
|---|---|---|
| 0.0–0.9 | No Effect | Too easy to trigger adaptation — a recovery walk, gentle yoga |
| 1.0–1.9 | Minor | Light stimulus — an easy recovery run, a casual ride |
| 2.0–2.9 | Maintaining | Enough to hold current fitness — a typical easy-to-moderate session |
| 3.0–3.9 | Improving | Driving adaptation — a solid training session |
| 4.0–4.9 | Highly Improving | Strong stimulus that needs recovery — a long run, hard intervals |
| 5.0 | Overreaching | Exceptional effort — race day, an ultra, an extreme session |
A 5.0 should be rare. Seeing it regularly means either the session genuinely was extreme, or your zone configuration needs updating.
The aerobic score
The aerobic score reflects how much the session stressed your aerobic system. It is driven by how long you trained and how hard, with diminishing returns — a 3-hour easy run does not score the same as a 90-minute threshold session.
What raises it
- Longer sessions
- Time in Z2 and Z3, aerobic base and tempo work
- Time in Z4, which has outsized aerobic impact per minute
What keeps it low
- Short sessions. Under 20 minutes rarely scores above 2.0
- Time entirely in Z1, where recovery pace contributes little
Typical scores
- 30 minutes easy Z2 → about 2.0
- 60 minutes Z2 → about 3.3
- 90 minutes Z2 plus 20 minutes Z3 → about 4.5
- A marathon or ultra → 5.0
The anaerobic score
The anaerobic score reflects how much the session stressed your anaerobic system. It combines time above your anaerobic threshold with peak heart-rate intensity.
What raises it
- Time in Z4, above AnT — the direct anaerobic stimulus
- High maximum heart rate relative to your AnT, which catches short intense bursts
- Short, hard sessions. The score dampens for very long ones, because sustained high intensity shifts toward aerobic metabolism
What keeps it low
- Sessions entirely below AnT, in Z1–Z3
- Long slow runs, even with some Z4 time, through duration dampening
- Low maximum heart rate relative to your threshold
Typical scores
- An easy Z2 run → 0.0
- A moderate run with a few hard hills → 0.5–1.5
- A tempo run with threshold intervals → 2.0–3.0
- A hard interval session, 15 minutes or more in Z4 → 3.0–4.0
- A race effort or all-out intervals → above 4.0
Most sessions produce minimal anaerobic stimulus. Above 2.0 means real high-intensity work.
Classification
Alongside the scores, each activity is classified Low Aerobic, High Aerobic, or Anaerobic:
| Category | Rule |
|---|---|
| Anaerobic | 15% or more of the time in Z4 |
| High Aerobic | 20% or more of the time in Z3 |
| Low Aerobic | Majority of the time in Z1 and Z2 |
Data sources
The scores use the best data each activity carries, in this order:
- Johnston zone distribution — time-in-zone data from your device translated to the Johnston 4 zones using your LT1 and LT2. The most accurate source.
- Average and maximum heart rate — where zone distribution is missing, scores are estimated from heart rate reserve and session duration.
- Garmin Training Effect — where there is neither zone data nor a configured Johnston model, the device's own values pass through unchanged.
The source label on each score says which of the 3 was used.
Intensity compliance
Weekly: the 80/20 check
Basecamp flags excessive intensity when less than 80% of your weekly training time is in Z1 and Z2. Chronically exceeding the 20% share of hard work raises fatigue faster than it raises fitness. This follows the polarized training model (Seiler, 2010).
Per activity
For runs intended as Z2 aerobic base, Basecamp flags excessive intensity when more than 10% of the session sat in Z3 or above. This catches easy runs drifting into tempo.
Accuracy and limits
The model was calibrated against 487 real activities with device-computed values as ground truth:
| Score | Mean absolute error | Within ±1.0 | Correlation |
|---|---|---|---|
| Aerobic | 0.41 | 87% | 0.91 |
| Anaerobic | 0.60 | 71% | 0.57 |
The anaerobic score is the weaker of the 2. Anaerobic training effect depends on factors heart-rate zone data does not capture — VO2max, cumulative load, recovery state. Lactate test results and body composition may improve it in a later version.