Training load

Load is Ergon's single measure of how hard a session was: time in each zone, weighted by how hard that zone is. This is the canonical write-up — how the number is built, where the boundaries come from, and where they stop being trustworthy.

The formula

Split the workout into the five training zones, then:

Load = minutes in zone × zone weight, summed across zones, with weights 1 / 2 / 3 / 4 / 8 for Recovery through TR. The jump to 8 is deliberate — all-out effort carries a disproportionate physiological cost, and a linear weight would understate it. A 30-minute steady UT2 row scores 60; a 20-minute race spending 15 minutes at AT and 5 at TR scores 100.

The model is a descendant of the Edwards/Banister TRIMP (TRaining IMPulse) family — the same time-in-zone idea, adapted to rowing's zone vocabulary.

Two signals

Every workout is scored on up to two independent streams:

• Power — external load: what you actually did. Derived from watts (which come from pace), so it exists for essentially every erg workout, strap or not.
• Heart rate — internal load: what the work cost you physiologically. Requires a monitor covering at least 80% of the workout, and a max HR in Settings. Below that, the HR score is blank rather than wrong.

Both are computed and stored whenever their signal exists, and they're never blended — they measure different things, and the gap between them is itself informative: heart rate running hotter than power at equal output is accumulating fatigue.

Choosing the basis

One of the two streams — your load basis — drives the headline Load, Fitness, and Form numbers. Settings → Load basis. Power is the default. Switch to Heart rate if you train by internal effort and wear a strap consistently; Ergon rescores your history for the new basis when you flip it.

The 0–21 daily scale

Daily Load is presented on a 0–21 scale — 0–5 light, 5–10 moderate, 10–15 hard, 15–21 max effort. The scale is quantile-calibrated to your own history, so "hard" means hard for you.

Why not TSS?

TSS is the cycling-world standard, built on a single functional threshold power and a normalized-power model tuned for variable outdoor riding. On the erg, output is already clean and continuous, and rowers think in UT2/UT1/AT/TR, not %FTP. A time-in-zone model speaks that language directly, works identically for heart rate and power, and degrades gracefully when one signal is missing.

Honest limits

• Power scoring needs a 2K reference. Without one (entered or estimated), the power score falls back to a rough linear watts approximation — usable, but it under-weights intensity. Enter your 2K watts in Settings → Training zones for zone-weighted scoring.
• The streams were calibrated, not proven equal. The power boundaries are defensible as an external-load measure on their own terms; they are not tuned to reproduce your heart-rate Load, and they shouldn't be.