Published Jul 3, 2021 · Updated Sep 10, 2026
Track your aerobic and anaerobic thresholds from DFA alpha 1, the heart rate variability metric, with the AI Endurance app. This guide covers every device that records it: Garmin and Suunto watches and bike computers, the Hammerhead Karoo with our on-device extension, and the Apple Watch with Watchletic.
TLDR: In short, DFA (detrended fluctuation analysis) alpha 1 measures the noise spectrum of your heart. As you ramp up the intensity of a workout and your heart has to work harder, the kind of noise - which the value of DFA alpha 1 represents - changes. Recent research has shown that DFA alpha 1 crosses below 0.75 at your aerobic threshold [1] and below 0.5 at your anaerobic threshold [2]. For a more detailed explanation, check our in-depth blog post about DFA alpha 1.
DFA alpha 1 might prove to be a groundbreaking advancement to correctly set our training zones and track fitness. It only requires you to wear a heart rate monitor that tracks HRV (Polar H10 recommended). This way, you will be able to
Imagine being able to detect your fitness level during most activities that are hard enough to cross either threshold, without even thinking about fitness testing. This is what AI Endurance does.
Use a heart rate monitor that records high quality HRV data. The Polar H10 remains the most recommended strap for HRV measurements. Where possible, connect it via Bluetooth rather than ANT+, since Bluetooth transmission leads to fewer artifacts, see Bruce Rogers' blog.
Enable HRV logging on your device (Settings -> System -> Data Recording -> Log HRV, or Settings -> Physiological Metrics -> Log HRV) and pair a chest strap. Optical wrist heart rate does not record in-activity HRV, so the strap is required. Connect Garmin Download to AI Endurance and every activity with HRV data arrives automatically. To see DFA alpha 1 in real time during the ride, install the alphaHRV Connect IQ app.
Suunto is the simplest setup: every Suunto watch connected to a heart rate chest strap logs HRV automatically. Connect Suunto to AI Endurance and you are done.
Install the AI Endurance Karoo extension and your Karoo computes DFA alpha 1, respiration rate and power live on the device. Add the "AIE DFA A1" or "AIE RF" numbers, or the "AIE DFA A1 GRAPH" chart, to a ride screen. A Bluetooth chest strap is required, and the activity arrives in AI Endurance with the full HRV analysis.
Watchletic (version 3.1.0 or later) connected to a heart rate monitor calculates your DFA alpha 1 in real time, just like alphaHRV, and records the in-activity HRV directly into the activity it sends to AI Endurance.
Coros and Wahoo devices, and the indoor training apps Zwift, Rouvy and TrainerDay, do not record activity HRV data. Strava does not pass HRV through, so connect Garmin or Suunto directly rather than via Strava. Polar devices record in-activity HRV but do not share it with third-party apps. You can still train in Zwift while a Garmin or Suunto records in parallel, and AI Endurance analyzes that recording.
Your DFA alpha 1 data is available for each activity under "View Analysis" in the AI Endurance Dashboard.
We attempt to automatically detect your thresholds for any activity with HRV data if the ramping is sufficiently slow. For the aerobic threshold this means at least 4 min of continuously decreasing DFA alpha 1 past 0.75. For the anaerobic threshold, we need at least 6 min of continuously decreasing DFA alpha 1 past 0.5.
We also detect thresholds via clustering: a cluster threshold is the average of all pace/power values recorded during the first 30 minutes of an activity with DFA alpha 1 values close to 0.75 (0.5). Generally, cluster thresholds are more abundant than ramps.
Our AI automatically takes into account the detected thresholds from ramps and clustering for your performance predictions. No more fitness testing anxiety and fatigue - focus on your training plan and we’ll detect your thresholds automatically over time and keep your digital twin up to date.
We have also created dedicated ramp tests for cycling and running in the AI Endurance app. These make it as easy as possible for you to accurately test your DFA alpha 1 thresholds with Garmin and/or Zwift. Simply go to your AI Endurance Apps page and either
In both cases, you need Garmin Download to be connected to AI Endurance.
The aerobic threshold sets the upper bound of your Endurance training zone. Conversely, the anaerobic threshold sets the upper bound of your Threshold zone [4].
We automatically keep track of your training zones over time. As your fitness evolves, we notify you if your DFA alpha 1 data indicates an update to your zones might be warranted.
AI Endurance analyzes your DFA alpha 1 automatically on every ride and run. Try it free.
by Markus Rummel. Coaching endurance athletes well takes time. Reviewing data, adjusting plans, responding to how each athlete is recovering and progressing: there is a limit to how many athletes you can closely monitor before the quality of attention starts to drop.
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