Applies to every Range Freely app that shows it. Last updated 28 October 2026.
DFA α1 is a number calculated from the timing between your heartbeats. Researchers use it during exercise to look for the aerobic threshold. This page explains what it is, what the research does and does not say, and what you need for a reading that means something.
Your heartbeats are not evenly spaced. The gap from one beat to the next wanders, and the way it wanders has a pattern. Detrended fluctuation analysis (DFA) measures that pattern, and α1 (alpha-1) is its short-range result. When you are resting or riding easily the pattern is orderly and α1 sits near 1. As effort rises the pattern becomes less orderly and α1 falls, toward 0.5 at hard effort.
You may already know heart-rate variability (HRV), a widely used indicator of physical state. HRV summarises how much your beat lengths change, typically as an average size of the change from one beat to the next. DFA reads the same stream of beat lengths a different way: not how big the changes are, but how they relate to each other across a run of beats. That pattern shifts as effort rises, which is why DFA α1 is used to follow effort.
It is calculated from beat-to-beat intervals alone. It is not a heart rate, and it is not a measurement of your health.
Studies in endurance athletes found that α1 passed through about 0.75 close to the first ventilatory threshold (the aerobic threshold), and through about 0.5 close to the second, with weaker agreement. That gave athletes a way to look for the aerobic threshold during ordinary training, without a laboratory. The work is by Rogers and colleagues (Frontiers in Physiology 2021; J Funct Morphol Kinesiol 2021), building on Gronwald, Rogers and Hoos (Frontiers in Physiology 2020).
For many people an α1 of 0.75 is a good estimate of the first threshold (LT1 or VT1), which usually sits near the boundary between zones 2 and 3. It is not a law, and some people's physiology varies, so for them the heart rate at 0.75 sits away from their own threshold. Treat α1 as one marker among several and check it against how hard the effort feels, whether you can still talk comfortably, and any lab test you have had. Over a long steady effort α1 can also drift down as fatigue builds, which is real physiology and not an error, so compare readings from similar points in an effort. A resting reading is only a check that your strap is picking up clean beats. If α1 drops sharply while you are resting or sitting still, it may be tracking something other than your effort, such as strap contact or movement, so check the strap fit and moisture.
A number, and a status word that says how far to trust it. Filling and Converging: the first data is still arriving. Settling: the number is real but not yet reliable, and shown in grey. Preview: too few clean beats yet. Held: too few recent beats were usable, so the number is withheld rather than shown with false confidence. Invalid: the reading gave no meaningful value, usually from a disturbed signal. Stabilizing and Stable: how much steady data is behind the value.
Our calculation agrees closely with Kubios HRV Scientific from 47 to 190 beats per minute. Kubios is the software family used in the research behind the 0.75 figure. That tells you the arithmetic matches. It does not tell you what the number means for you.
In Range Freely: ECG Recorder, DFA α1 is always free.
How to run a steady-state test, which is how to find where α1 sits for you. For the questions people ask about the Recorder specifically, see the ECG Recorder FAQ.