Why not just duration?
The duration of a session says nothing about its intensity. A long run at an easy pace and a short threshold session can last the same amount of time, but the second one taxes your body far more. To steer your training without getting injured, you need a measure that captures real effort, not time spent.
TRIMP: a unit of effort
For each session, Baseload computes a TRIMP (from training impulse). It's a number that combines the duration and the intensity of the session. Intensity comes from your heart rate: the more time you spend in the high zones, the higher the TRIMP climbs. The calculation is weighted (a Banister-type model) to reflect the rising cost of high intensities.
- With heart rate: TRIMP factors in intensity minute by minute.
- Without heart rate (pool swimming, a session imported without HR): Baseload switches to an estimate based on duration and perceived effort — the session is never ignored.
When you log the perceived effort (RPE) of an endurance session, Baseload uses it to correct the TRIMP computed from your heart rate. A day when "everything felt hard" and a day with "light legs" at the same pace aren't counted the same way.
Elevation counts too
For running, walking and hiking, Baseload adjusts effort based on elevation gain (Minetti's metabolic model). A 10 km with 500 m of elevation gain costs noticeably more than a flat 10 km. Cycling is excluded : heart rate already captures the cost of the climbs there.
Acute load and chronic load
Once each session is measured, Baseload tracks two averages:
| Indicator | Window | What it represents |
|---|---|---|
| Acute load | ~7 days | Your recent fatigue — what you've just absorbed. |
| Chronic load | ~28 days | Your fitness — what your body is used to. |
Both are weighted averages (recent days count for more). The ratio between them is the heart of the prevention model: it's the ACWR.
Your volume, as real effort
Baseload expresses your weekly volume in TRIMP, not minutes. And the target isn't a universal figure : it's your own chronic load. In other words, the app compares you to yourself, to your fitness over the past weeks — never to another athlete.
TRIMP is an estimate of effort, not a physiological truth. It depends on the quality of your heart-rate data and the calibration of your zones. Baseload treats it as a robust signal at the scale of the week, not as a lab-grade measurement down to the individual session. More details on the limits page.