Published Jul 3, 2021 · Updated Oct 28, 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 and pair a chest strap: on current Garmin watches the setting is under Settings -> System -> Advanced -> Data Recording -> Log HRV; on Edge bike computers and older watches under Settings -> System -> Data Recording -> Log HRV, or Settings -> Physiological Metrics -> Log HRV. Firmware updates can reset this setting, so check it again after updating. 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 5 min of steadily rising intensity with decreasing DFA alpha 1 past 0.75. For the anaerobic threshold, we need at least 7 min past 0.5. The ramp has to happen within the first 30 minutes of the activity.
We also detect thresholds via clustering: a cluster threshold is the average of all pace/power values recorded during the first 45 minutes of a run (60 minutes of a ride, moving time) with DFA alpha 1 values close to 0.75 (0.5). Generally, cluster thresholds are more abundant than ramps, and both methods are weighted equally.
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. Respiration frequency (RF) is one of the more underused metrics in endurance training. Power, pace and heart rate usually dominate the conversation, but breathing rate adds something different. It responds quickly to changing workload, tracks perceived exertion well, and sits close to the physiology around ventilatory thresholds [1].
by Markus Rummel. We present the first results of AI Endurance's new capability to calculate Respiration Frequency (RF) from in-activity heart rate variability (HRV) data. RF demonstrates its potential in assessing the validity of HRV threshold determination.
Power meters are costly and we often can't afford one on every bike we own. AI Endurance calculates cycling power from activities without a power meter using heart rate, cadence and DFA alpha 1. The results are generally more accurate than speed based estimates such as Strava's estimated power. All you need is a heart rate monitor and ideally a cadence sensor on your bike and AI Endurance will estimate your power for every ride.
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.
