Nurik metrics glossary

Published September 30, 2026 · Source: internal product specifications, validated by Nurik's medical team

Recharge, ATOMIC and Load are Nurik's three proprietary scores. This page explains what each one measures, what data it's calculated from, and what each color band means — it's the same reference we use ourselves when writing the app.

Recharge

Question it answers: how charged are my batteries today?

Recharge is a 0–100 score that estimates how much battery your body has to train today. It's calculated once when you wake up and doesn't change during the day.

Inputs

Nighttime HRV (RMSSD), compared against the average of the last 7 nights
Resting heart rate, compared against the average of the last 7 nights
Previous night's sleep
Nighttime blood oxygen (SpO2), adjusted for altitude

Each component is compared against that person's own recent average, not against a population table or against other users.

Color bands

Band	Range
Green	≥ 67
Yellow	34 – 66
Red	< 34

These cutoffs (67/34) are what the app uses today; Nurik's medical team documents them as pending validation with real-world usage data, not as an established clinical threshold.

ATOMIC

Question it answers: how much and how should I move today?

ATOMIC is the day's movement goal: target minutes and session type (rest, active rest, easy, zone 2, hard, or a long easy outing), adjusted to the day's Recharge, the personal goal (health, performance, or body weight), declared weekly hours, and the week's accumulated training load.

Unlike Recharge, ATOMIC is not a 0–100 number: it's always shown with its unit ("ATOMIC · 45 min"), precisely so it isn't confused with Recharge.

How it adjusts the goal based on Recharge

Recharge	Effect on minutes	Allowed session types
Green	× 1.0	All, including a hard session if there's weekly room and load isn't high
Yellow	× 0.7	Easy or zone 2 (one notch less intense than planned); no hard session
Red	No minutes goal	Rest or optional active rest (max 30 min)

The calculation also factors in an acute:chronic load ratio (last 7 days' TRIMP against the average of the previous 28 days) as a conservative brake on load progression: that number is never shown to the user, only its effect on the goal. Its ability to predict injury has been fairly contested since 2020 (Impellizzeri et al.), so Nurik treats it as a conservative heuristic, not a safety guarantee.

Internal name

Behind the scenes, Nurik's code and technical documentation still call this concept "Readiness" (classes, files and comments weren't renamed). Since September 25, 2026, the name visible to app users is ATOMIC, to avoid confusion with how other wearable brands use the word "Readiness" (in those apps, "Readiness" usually means what Nurik calls Recharge).

Load

Question it answers: how much did I demand of my body today?

Load is a 0–100 score that measures the day's or a session's cardiovascular load, combining time and intensity from heart rate — not just minutes: 60 very easy minutes and 60 minutes of hard intervals don't generate the same Load.

How it's calculated

Load is based on Banister's TRIMP (training impulse), the classic internal-load model in sports science:

x = (HR − HR_rest) / (HR_max_effective − HR_rest), capped to [0, 1] TRIMP = Σ Δt[min] · x · a · e^(b · x) Male: a = 0.64 b = 1.92 Female: a = 0.86 b = 1.67

HR_max_effective is the maximum heart rate used in the formula, chosen in this order of priority: the one the user entered manually; if there isn't one, a maximum observed by the sensor that has already passed a plausibility filter; and if neither exists, an age-based estimate using Tanaka's formula (2001): HR_max = 208 − 0.7 × age. Any age-based HR max estimate carries an individual error of ±7–10 bpm, which propagates through the entire TRIMP calculation.

The a and b coefficients for "Male"/"Female" come from the original Banister/Morton model, which assumes a binary field; Nurik inherits them as-is, without its own validation for identities outside that binary.

The day's or session's accumulated TRIMP is mapped to Load's 0–100 scale with a logarithmic curve:

Load = 100 · ln(1 + TRIMP / 50) / ln(11), capped to [0, 100]

Load doesn't add up across sessions (two sessions with Load 50 don't make Load 100): what adds up is TRIMP, and Load is recalculated over that total using the same formula.

Reading the bands

Load	Band	Reading
0 – 24	Light	Little effort for the heart; good for recovery
25 – 49	Moderate	Enough movement to add up without accumulating fatigue
50 – 74	High	Demanding day; prioritize sleep and nutrition
75 – 100	Very high	Load that usually calls for one or two easy days after

Differences of less than 5 points between two days fall within the expected error margin of the optical heart rate sensor during exercise and aren't interpreted as a real change.

Terminology note

Recharge, ATOMIC, Load and Nurik are not translated into any language: they're the product names of Nurik's proprietary scores, calculated with proprietary formulas, and stay identical in Spanish and English so they're recognizable in any market. The rest of the app's terms (sleep, stress, resting heart rate, blood oxygen, heart rate zones) are translated, since they're generic physiological concepts.

This page is general educational information, not medical advice. Nurik is not a medical device: Recharge, ATOMIC and Load are estimates from wrist sensors, not clinical tests, and they do not diagnose disease or replace a health professional's evaluation.

Source for the formulas and definitions: Nurik's internal product specifications, reviewed by the project's medical consultant based on Banister (TRIMP model), Hopkins 2009 and Plews 2013 (smallest worthwhile change applied to HRV).

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