DFA α1 Calculator
Determine your aerobic and anaerobic threshold from RR-interval data — no lactate test, directly in your browser.
Upload Step Test Recording
Complete recording of all steps in one file
Garmin (.fit) · Polar Sensor Logger (.txt) · HRV Logger (.csv) · CSV since_start,RR
Step Test Protocol
- 1. 10 min warm-up (will be filtered out)
- 2. 4–6 steps of 4–6 min each at constant intensity — record RR continuously
- 3. Example running: 7:00 → 6:30 → 6:00 → 5:30 → 5:00 min/km
- 4. Export and upload — steps are automatically detected and can be adjusted
What is DFA α1?
A nonlinear HRV metric that describes the fractal correlation structure of your heart rate.
How it works
DFA α1 measures the self-similarity (fractality) of your RR intervals over short windows (4–16 beats). At low intensity the HRV pattern is complex and fractal (α1 near 1); at high intensity it becomes more regular (α1 drops toward 0.5 and below).
The thresholds
α1 ≈ 0.75 correlates with the aerobic threshold (AeT, ~2 mmol/l lactate). α1 ≈ 0.5 marks the anaerobic threshold (AnT, ~4 mmol/l). These values have been validated in several studies against lactate step tests.
Privacy
All calculations run exclusively in your browser. Your RR data never leaves your device. No server, no tracking of your heart rate data.
| α1 Value | Zone | |
|---|---|---|
| > 0.9 | Well below AeT | GA1 · ZONE 1–2 |
| 0.75–0.9 | Below AeT | Upper GA1 · ZONE 2 |
| 0.65–0.75 | Aerobic Threshold (AeT) | ~2 mmol/l lactate · ZONE 2/3 |
| 0.5–0.65 | Between AeT and AnT | Tempo · ZONE 3–4 |
| 0.45–0.55 | Anaerobic Threshold (AnT) | ~4 mmol/l lactate · FTP |
| < 0.45 | Above AnT | VO₂max range · ZONE 5 |
Based on research by Gronwald et al. (2020) and Mateo-March et al. (2022). DFA α1 works best for endurance athletes using a chest strap HRM (Polar H10, Garmin HRM-Pro).
Feedback or questions? [email protected]