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Istria 100 by UTMB
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Istria 100 by UTMB® 42K

UTMB World Series
42.0km·950m+
April 12, 12:00 PM
Umag,
Croatia
utmb·source

Race Pace Calculator · GPX Analyzer · Trail Finder

Other races: Croatia

Read

  • Types of Runs and What Each Workout Actually Trains
  • Hill Training for Trail Runners: Train the Descents
  • Downhill Running Muscle Damage: Why Descents Wreck Quads

Full calendar: CroatiaMarathon trail race calendar

Istria 100 by UTMB® 42K · Race profile

Distance
42.0km
Gain
950m+
FlatKM
49.9
Max
368m
Min
0m

About Istria 100 by UTMB® 42K

Istria 100 by UTMB® 42K is the 42.0km trail race at Istria 100 by UTMB 2025 (Umag, Croatia). The race starts on April 12, 2025 at 12:00 PM.

Race strategy

Run hard on the first mountain, but save energy for the second.

  • 281m descent. Go easy, save your quads.
  • The finish is runnable. Save your legs to run it all the way.
  • Go easy on the first downhill, save your quads on the descents until 12.3km, then run your race pace.
  • Start · 0.0km–2.0km · Race-day nerves push your heart rate up: don't follow the crowd, find your own rhythm.
  • Settle in · 2.0km–7.7km · Plus 1 more climb and 1 descent. Ease in: hold back more than feels necessary. The race is still ahead. Climb by heart rate or breathing, not pace.
  • Work · 7.7km–17.0km · Descent of 281m averaging 6%. Plus 1 more climb. This is where the race is built: steady, solid effort. Climb by heart rate or breathing, not pace. This descent is hard on the legs: short steps, stay in control, poles if you have them.
  • Home · 17.0km–42.2km · 25.2km of runnable trail, high point 369m. Build to the finish: leave whatever you have left out on the course. Running pays off here: run wherever you can.

Course

The course climbs 950m+. With 23m/km of climbing, the course is predominantly runnable. By gradient, 18% of the distance is uphill, 25% downhill and 57% flat. The longest climb runs 4.8km at an average 6.9% grade (333m of vertical). The longest descent runs 4.6km at an average 6.0% grade (281m of vertical). The steepest climb averages 21.9% over 1.0km. The steepest descent drops at 20.9% over 0.3km. Surface: 37% trail, 35% smooth, and 24% road. Flat-equivalent effort: 49.9 FlatKM.

Summits

The course also passes close to Sv. Jure (384m), Pelegrin (185m), and Starola (165m).

Poles

Poles bring little benefit here: only about 1.7km of pole-friendly terrain.

Quad damage

Quad damage risk is low (index 13 of 100): a few descents worth noting, none of them decisive.

  • Go easy on the first downhill, save your quads on the descents until 12.3km, then run your race pace.
  • #1 · 7.7–12.4 km · 281 m D−, -6.0% · 29.8 km ahead → control

Results

643 finishers completed the 2025 edition. Men's winner: Sammy Rotich Chelangat (Kenya) in 2:51:46. Women's winner: Martyna Mlynarczyk (Poland) in 3:15:01.

This page has the full results and splits, a pacing and nutrition planner, a gradient matrix, an interactive elevation profile and historical weather for Istria 100 by UTMB® 42K.

Other distances of Istria 100 by UTMB 2025Istria 100 by UTMB® 168K (168km)·Istria 100 by UTMB® 110K (110km)·Istria 100 by UTMB® 69K (69.0km)·Istria 100 by UTMB® 21K (21.0km)

Other editions of Istria 100 by UTMB® 42K2027·2026

Official websiteistria.utmb.world