Every number, and where it comes from.

Calories burned: a range, never one number

• For each session: the session type’s MET value × your body weight in kg × hours × an effort factor.
• The effort factor is 0.6 + 0.08 × effort, where Easy is 3, Moderate 5 and Hard 7.
• The result is shown from 20% below to 20% above, rounded to 10 kcal.
• If you add your height, birth year and sex (female or male), your predicted resting energy (the Mifflin-St Jeor equation, 1990) replaces body weight alone. Otherwise the weight-only version is used.
• MET values come from the 2024 Adult Compendium of Physical Activities (Herrmann et al., 2024, pacompendium.com). A few of them:

Why a range. MET values are averages for adults, and people differ a lot. The ±20% shows that spread; it’s a display choice, not a measured error margin. Watches aren’t a reference either: in one review, no brand estimated energy use within acceptable error (Fuller et al., JMIR mHealth and uHealth, 2020).

Your plan’s burn. Fuel can show what your weekly plan burns per day, counted at an effort between Moderate and Hard, also as a range.

When the range is hidden

• No body weight, no calories: they stay hidden everywhere until you add your weight. Knuckly uses your latest weigh-in.
• A day or week total appears only when every session in it has an estimate. A partial sum would look like the whole, so none is shown.
• An older session with a type the app no longer lists shows no estimate.
• There is no “eaten minus burned” number.

Food: sources and licences

• Built in, offline: USDA FoodData Central, SR Legacy (April 2018), 7,283 foods, public domain (CC0 1.0). Source: U.S. Department of Agriculture, Agricultural Research Service, FoodData Central.
• European basic foods, offline: ANSES Ciqual 2025, 3,303 foods, Licence Ouverte / Etalab 2.0. Tagged “EU” in search.
• Packaged foods: Open Food Facts (openfoodfacts.org), ODbL. Contacted only when you search packaged foods or scan a barcode; it receives the search words or the barcode, your phone’s language and the app’s name and version. Knuckly uses the label values per 100 g, never Open Food Facts’ estimated values, and drops values above 900 kcal or 100 g per 100 g as implausible.
• Your own foods: typed from the label, per 100 g.
• Each food entry keeps the values it was logged with, so a later database update never rewrites your history.

Missing stays missing

• A food without, say, a protein value adds nothing to protein, and the total shows it’s incomplete.
• When foods have no calorie value, the day says how many and that the real total is higher.
• The protein, carb and fat split is shown only when every food has all three values.
• Food is compared only with your own daily target, never labelled good or bad.

Training: effort, weeks and progress

• Effort is your pick of Easy, Moderate or Hard (3, 5 and 7 on a 10-point effort scale, after the session-RPE method of Foster et al., 2001).
• Consistency is weekly: weeks on target ÷ finished weeks that had a target. Past weeks keep their own targets, and a rest-day swap keeps the week’s target.
• Progress insights come from your log only: totals, your easy-to-hard mix, sparring and personal bests. Nothing in them is estimated.
• Daily check-ins (sleep, soreness, energy) are for you to spot patterns. They never change a number.

What Knuckly never estimates

• A recovery percentage or readiness score
• Hours until you’re recovered
• Injury risk, or a “sweet spot” for training load
• Whether you’re “ready for a hard session”

Sessions, minutes and effort can’t support these, so showing them would be false precision. The evidence for predicting injuries from training-load ratios is contested (Impellizzeri et al., 2020).

Lessons and technique guides

• The 60 Learn lessons are general information in our own words, not medical advice. Each lists its sources with the year: position stands, consensus statements, reviews and key studies. Each source is named with its year, so you can read it yourself.
• The 24 technique guides are written steps, key points and common mistakes, based on published coaching books. The 72 pro tips link to the coaching sources and competition rules they’re based on, checked on 28 September 2026.