How activity load is calculated
Activity load is a 0–100 reference score for where today's expenditure sits within your own past 30 days — 70 means "heavier than about 70% of your usual days", not any absolute training standard.
Inputs and weights
- Physical effort (Apple's MET-based measure) — 50%
- Active energy — 30%
- Exercise minutes — 20%
Why a percentile, not an absolute number
The same 500 kcal means very different things to different people. The consensus approach to load monitoring is to read current load against the individual's own recent load — the meaningful signal is a spike relative to your own history, not an absolute figure.
So we compute where today's expenditure falls within your own window. Which also means: if you raise your training across the board, load drifts back toward the middle, because your "usual" has moved. That is by design, not a fault.
Low load is not a bad thing
Load is not read like recovery. A low recovery score is worth noticing; a low load simply means a light day — possibly exactly the rest you needed. So in Vita a low load renders in a neutral colour, never an alarming one; only a high load (around 85 and above) prompts easing off.
Limitations
- Needs at least 7 days of activity data before a percentile exists.
- Strength training is understated — its metabolic cost is far below the stress it actually imposes.
- Time without the watch cannot be counted, and activities with little wrist motion (cycling, for instance) tend to read low.
- This is a reference index, not a training prescription.
References
Bourdon PC, Cardinale M, Murray A, et al. Monitoring Athlete Training Loads: Consensus Statement. International Journal of Sports Physiology and Performance. 2017;12(S2):S2-161-S2-170.
What it supports：The consensus method for monitoring training load, including the internal/external load distinction.
Gabbett TJ. The training—injury prevention paradox: should athletes be training smarter and harder? British Journal of Sports Medicine. 2016;50(5):273-80.
What it supports：Risk comes from a spike relative to one's own recent load — why load is a percentile within your own window rather than an absolute number.
Ainsworth BE, Haskell WL, Herrmann SD, et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Medicine & Science in Sports & Exercise. 2011;43(8):1575-81.
What it supports：MET values for physical activities — the standard table behind intensity conversion.
Related metrics
Every metric on this page is a reference index for observing your own trends. It is not medical advice and cannot replace a professional diagnosis. If you have health concerns, consult a qualified clinician.
Source module: lib/vitality/score.ts · computeLoad
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