Heart rate zones: how the Ultrahuman Ring measures training intensity

What are heart rate zones?

Heart rate zones are five intensity bands that divide the range between rest and maximum effort.

Zone 1 covers 50 to 60% of your maximum heart rate, Zone 2 covers 60 to 70%, Zone 3 covers 70 to 80%, Zone 4 covers 80 to 90%, and Zone 5 covers 90 to 100%.

Zone 1 and Zone 2 primarily stress the aerobic system and fat metabolism; Zone 3 approaches the lactate threshold; Zone 4 and Zone 5 push into anaerobic contributions and place the greatest demand on VO2max.

Sports scientists use five-zone thresholds derived from graded exercise tests with blood lactate and ventilatory measurements as the reference standard for precision training prescriptions.

How does the Ultrahuman Ring measure heart rate zones?

The Ring AIR measures heart rate by shining green light from an LED array on the ring's inner surface into the tissue of your finger.

That per-minute heart rate reading is then placed onto a five-zone ladder. The ladder is built from your personalized maximum heart rate, computed from your age using the Tanaka formula.

For a 35-year-old, the estimated maximum would be 208 minus (0.7 times 35), which is approximately 184 beats per minute.

Zone 2 for that member would run from about 110 to 129 bpm and Zone 4 would run from about 147 to 166 bpm.

During a recorded workout, the app tracks how many minutes you spend in each zone in real time.

When the session ends, it stores the zone-time breakdown. The weekly cumulative view sums zone-time from every session in the current seven-day window, so you can see whether your week has been weighted toward aerobic base work, threshold effort, or high-intensity intervals.

Why did Ultrahuman build it this way?

The most widely cited maximum heart rate rule, 220 minus age, was never derived from a controlled study.

Tanaka and colleagues established that their age-based formula fits the data significantly better, particularly for adults over 40, where the older rule systematically underestimates maximum heart rate. Using it means zone boundaries shift appropriately with age rather than applying a one-size-fits-all correction.

Five zones, not three. A three-zone model (easy, moderate, hard) is simpler but collapses information. The five-zone model separates the aerobic base (Zones 1 to 2), the threshold region (Zone 3), and the high-intensity domain (Zones 4 to 5) into distinct bands.

Elite cross-country skiers, for example, have their five-zone thresholds defined in graded exercise testing by both ventilatory threshold and blood lactate, allowing precise prescription of which zone a session targets. That same specificity is what makes a five-zone view useful for a Ring member tracking whether a week's training leaned toward base or intensity.

Weekly cumulative, not only per-session. Training adaptation depends on accumulated stress over days, not a single session. A study following 41,930 US adults for nearly ten years found that meeting more movement guidelines over time was linked to progressively lower cardiovascular death risk, with those meeting all three guidelines showing a 47% lower CVD mortality risk than those meeting none. Weekly zone accumulation reflects this principle: what matters is the pattern over the week, not any individual session.

What does the research say about training intensity distribution?

The five-zone model has practical value because different zones produce different physiological adaptations, and the balance between them shapes training outcomes.

A meta-analysis comparing training intensity distribution models found that lactate-threshold training came out on top for improving VO2max, while high-intensity interval training came out on top for time-trial performance. Importantly, no single model showed a clear advantage over polarized training for VO2max.

In a randomized controlled trial of 120 recreational marathon runners, a polarized training approach produced 30% greater marathon time improvement than a pyramidal approach (11.3 versus 8.7 minutes, a statistically reliable difference). Looking at how individuals responded, training experience was the strongest predictor of which approach worked better: novice athletes tended to benefit more from pyramidal loading, while experienced athletes responded better to polarized training. The authors concluded that person-to-person variation is too large for universal prescriptions.

Wearable PPG sensors show strong accuracy during steady-state aerobic exercise. A validation study comparing PPG-derived heart rate against ECG during endurance and resistance exercise found strong agreement during endurance exercise, with most readings within roughly plus or minus 10 bpm of the ECG reference. Accuracy declined during resistance exercise due to increased movement artifact, a finding consistent across PPG wearable research.

For zone-specific measurement during maximal exercise, a validation study of PPG-based heart rate across five predefined intensity zones during a maximal treadmill test found that the typical error declined from 2.9% at 50 to 60% of maximum heart rate to 0.6 to 0.75% at zones above 70% of maximum heart rate. Note that this study used a wrist-worn smartwatch; a finger-worn ring occupies a different anatomical position with different motion-artifact dynamics, so these figures characterize general PPG zone-tracking behavior rather than Ring-specific performance. The better-than-expected performance at higher absolute heart rates reflects that motion artifact at high intensity is less disruptive when the heart rate itself is high enough that small absolute errors represent a smaller percentage of the true value.

How do heart rate zones show up in the Ultrahuman app?

During a workout that members start in the Ultrahuman app, the training zones card appears in real time, showing which zone the current heart rate falls into and how long has been spent in each zone so far in the session.

The zones are color-coded and labeled with their percentage of HRmax, so members can see immediately whether they are in the aerobic base range or approaching threshold.

When the session ends, the workout summary card includes a zone-time bar chart alongside the other session metrics (steps, active calories, duration).

Tapping into the movement section of the Ultrahuman app shows the weekly aggregated view, where zone-time from every session in the rolling seven-day window is combined into a single stacked view. This lets members track whether their training week is balanced toward endurance, threshold, or intensity work.

The zone feature connects directly to the workout mode that detects and records your sessions and contributes to the overall Movement Index that the app calculates daily. Heart rate data captured during workouts also feeds the resting heart rate trend, which reflects cardiovascular adaptation over weeks of consistent training.

If you want to act on what the zone chart shows, the Ultrahuman blog covers the practical training side this page deliberately leaves out: a guide to how to train in each zone using the 80/20 approach, a companion piece on how to structure aerobic base and threshold work across a training week, and guidance on choosing cardio vs strength for your goal.

The zone chart is a practical training guide, not a lab-calibrated measurement.