Health-metric references, measurement methodology and calculators, with source support and model limitations described on each page. For people who already own a wearable and want to understand their numbers.
Explore Metrics Library Open CalculatorsDo you use Oura, Ultrahuman, Whoop, or Garmin? Start with the metric that matters most to you.
Oura → Ultrahuman → Whoop → Garmin → See all devices →Definitions, measurement methodology, normal ranges by age and sex, and which devices measure each metric — all source-cited.
The time variation between consecutive heartbeats. One of the strongest proxies for autonomic nervous system fitness.
View metric →Percentage of time in bed actually spent asleep. Clinical benchmark is ≥85%. Most wearables underreport this.
View metric →Maximum oxygen uptake during peak exertion. The single strongest predictor of cardiovascular longevity in published literature.
View metric →Beats per minute at complete rest. AHA defines normal as 60–100 bpm; highly trained athletes regularly register 40–60.
View metric →Slow-wave sleep drives physical recovery, immune function, and memory consolidation. Declines significantly with age.
View metric →Rapid eye movement sleep regulates emotional processing and procedural memory. Target: 20–25% of total sleep time.
View metric →Time from lights-out to sleep onset. Clinical range: 10–20 minutes. Under 5 minutes signals sleep deprivation.
View metric →Breaths per minute during sleep. Elevated baseline is an early illness marker tracked by Oura, Garmin, and Whoop.
View metric →Deviation from personal baseline during sleep. More useful than absolute readings. Key signal for illness and recovery.
View metric →Proprietary composite scores (Oura Readiness, Whoop Recovery) explained — including how algorithms weight each input.
View metric →Five tools with different methods. HRV results use a reference table with unverified provenance; the biological-age tool is Nyxova’s own unvalidated model. See each tool’s limitations.
Position on Nyxova’s configured RMSSD table; not a verified population percentile.
Open calculator →Enter time in bed and actual sleep time. Get your efficiency percentage and clinical category.
Open calculator →ACSM normative table lookup. Poor / Fair / Good / Excellent / Superior classification by age and sex.
Open calculator →Compare your resting heart rate against AHA population norms.
Open calculator →Explore Nyxova’s own unvalidated model using sleep, resting heart rate, VO₂ max and activity.
Open calculator →Reference tables by age and sex. Source support varies: the HRV table’s exact population-percentile provenance is unverified. No paywalls, no email required.
Configured RMSSD values by age and sex; exact population-percentile provenance unverified.
View table →ACSM classifications from poor to superior by decade.
View table →AHA normal ranges, athlete ranges, age stratified.
View table →PSG-measured population data by decade.
View table →N3 slow-wave percentages across the lifespan.
View table →Normal REM proportion across age groups.
View table →Clinical sleep-onset ranges by age.
View table →Normal breathing-rate ranges during sleep, by age.
View table →Algorithm explanations, score interpretations, and known measurement limitations — for popular wearables and sleep trackers.
Readiness Score, Sleep Score, and Activity Score — what inputs they use and how they're weighted.
Read guide →Ring PRO (with Ring AIR as the alternative) — Recovery Score, Sleep Index, and Movement Index, and what Ultrahuman does not publish.
Read guide →A bedside sleep monitor for the room — temperature, humidity, light, noise, air quality and snoring.
Read guide →How HRV, stress, sleep quality, and activity combine into the 0–100 Body Battery score.
Read guide →Green / Yellow / Red recovery explained. HRV, resting HR, sleep performance, and respiratory rate inputs.
Read guide →Health app metrics including HRV (SDNN), VO₂ max estimation, sleep stages, and AFib detection.
Read guide →Fitbit-powered metrics — Active Zone Minutes, sleep score, and daily readiness explained.
Read guide →