Race Effort Estimator

ITRA km-effort is the International Trail Running Association's standardised effort unit for trail races. The official ITRA formula uses gain only: km-effort = distance + gain/100. TrailMath extends this by adding descent cost (+ loss/150), because steep descents cause real eccentric muscle damage (Minetti, 2002) that the gain-only formula ignores. A race with 100km and 6,000m of gain/loss has a TrailMath km-effort of 160 - equivalent in effort to running 160km flat.

The estimated UTMB Index (0-1000) shown here comes from a log-linear model of score against flat-equivalent speed and course size, fitted to results read from public utmb.world runner profiles. It is reported as a range rather than a single number because the calibration is approximate. This is useful for comparing yourself across different races over time, but is not your official ITRA Performance Index or UTMB Index - both of those use proprietary formulas.

Official ITRA Performance Index is calculated by ITRA using a weighted average of up to your 5 best race scores over the past 36 months, with each race scored against the field of finishers. It requires ITRA to have official race data and registered finisher times. Check your official index at itra.run.

UTMB Running Stones are awarded by UTMB World only for designated UTMB-World Series races, based on km-effort thresholds and cutoff compliance. The indicative tier shown here uses the 2023 threshold table (15/35/60/100/150/200 km-effort = 1-6 stones) as a rough guide for non-designated races. Check official qualification rules at utmb.world.

ITRA. Performance Index methodology. itra.run/FAQ/PerformanceIndex UTMB World. Running Stones rules. utmb.world/en/sports-system