How EveryBand calculates Strain

EveryBand Strain is an independent index of observed daily exertion. It combines covered intensity and time, distinguishes recorded workouts from background effort, and considers supported movement and steps. It is not a percentage of your physical capacity or the amount of exercise you can safely perform.

The Strain index can exceed 100. Its scale differs from EveryBand's bounded Sleep and Recovery scores, and from another app's Strain scale. A value of 100 does not mean a full day, a personal maximum or a limit you must reach.

This describes the current documented implementation reviewed on 15 October 2026. Installed beta builds may differ. An implemented equation is not clinical validation or evidence that the score predicts injury, fatigue or fitness gains.

Ordinary Strain scoring needs a valid resting-heart-rate reference, an estimated maximum heart rate above that reference, and at least two heart-rate points with positive covered time. The age-based maximum uses the Tanaka equation, 208 − 0.7 × age. It provides an estimate, not a measured personal maximum. That research does not validate EveryBand's weighting or Strain index.

For each supported interval, intensity is expressed as heart-rate reserve:

intensity = (heart rate − resting heart rate)
            / (estimated maximum − resting heart rate)

The value is bounded from zero to one before being squared and integrated over covered time. Higher intensity therefore adds load faster than the same duration near rest. Missing age/profile context or an unusable resting reference can prevent a score even when other activity is visible.

Covered time overlapping a recorded workout receives full heart-rate weight. Other covered time receives half weight. A workout label can therefore matter to the calculation; the score does not treat every elevated heart-rate minute as the same kind of effort.

Movement produces a separate dose from covered motion intensity. Steps produce another bounded dose. Because heart rate, motion and steps can observe the same activity, the current calculation uses the largest supported daily dose rather than adding all three together. This reduces repeated counting of one bout of exertion.

These alternatives do not remove the ordinary score's required heart-rate and reference inputs. A step count alone is not a promise that Strain will appear.

The current mapping is logarithmic:

Strain = 100 × log(1 + daily dose / 10) / log(18)

Additional load becomes progressively harder to add to the displayed index. The result is rounded and can exceed 100. A separate internal load-pressure value is capped at 100 for calculations such as Energy Reserve. The displayed Strain index and that capped input should not be treated as identical.

Heart-rate and motion intervals longer than five minutes are not filled by the Strain calculation. Sparse or missing observations can therefore underrepresent a day's load. A displayed number does not prove complete-day coverage.

Target Strain is a separate daily heuristic based on settled Recovery and previous completed days. It considers recent seven-day and 28-day load context and produces a range with history-based confidence. Today's accumulating Strain does not move its own target.

Historical days must be finalized and sufficiently covered. The coverage rule accepts a trustworthy daily steps aggregate or at least eight hours of unioned heart-rate/motion coverage, without filling long gaps. Limited history reduces confidence; that label is not a medical confidence interval or a safety guarantee.

The range is context for balancing recorded activity and rest. It is not a prescription to exercise through illness, pain or exhaustion, or a prediction that staying inside the range prevents harm.

Heart-rate load is not a complete measurement of muscular work. Heavy lifting can create substantial local fatigue without the same cardiovascular trace as endurance exercise. Logging sets and external load does not validate a muscular-strain model; EveryBand keeps unsupported strength physiology unavailable.

Fit, movement artifacts, profile estimates, missing workout labels and source changes affect the result. Comparisons are most useful when the method and recording conditions are understood. EveryBand does not claim its index reproduces WHOOP or Bevel scores, or that it is more accurate than either.

EveryBand is independent and is not affiliated with, endorsed by or sponsored by WHOOP, Apple or Bevel. Third-party names are used only for factual comparison and interoperability.

Written by EveryBand. Published October 16, 2026; reviewed October 16, 2026. Product descriptions are subject to the installed build; third-party features and terms may change.

• Tanaka, Monahan and Seals: Age-predicted maximal heart rate revisited

EveryBand is an independent app and is not affiliated with, endorsed by, or sponsored by WHOOP, Apple, or Bevel. Third-party product names and trademarks belong to their respective owners and are used only for factual compatibility and interoperability descriptions.

Other app and device names belong to their owners. EveryBand is also independent of Sixteen and its publisher. For corrections, contact EveryBand.

• How the estimates workRead the full explanation.
• How EveryBand calculates RecoveryEveryBand Recovery combines nightly RMSSD, resting heart rate and Sleep with personal history. It needs the current night and two prior complete baseline nights.
• How EveryBand estimates StressEveryBand Stress is a 0–100 physiological estimate from heart rate relative to rest, with available HRV context and movement filtering. It does not measure emotions.
• How EveryBand estimates EnergyEnergy Reserve is a wellness index combining available Recovery, Sleep, Strain and Stress. Calorie expenditure is a separate estimate with different inputs and limits.
• Data sources and compatibilityRead the full explanation.