Free 16-Week Training Plan for Istria 100 by UTMB 21K
Train for early-season ultra distance with rolling Istrian climbs, night running, and runnable coastal sections.
At 21.5 km with 157 m of elevation gain, this is a fast, punchy distance where speed and hill strength both matter. At 7 m of vertical per kilometer, much of the course is runnable — the plan focuses on building your aerobic cruising speed while preparing you for the steeper sections. The official cutoff is 4 hours, so pace management starts from week one.
Race date: Sun, 4 April 2027Open entry21.5 km · 157 mStart: 10:00
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Continue Istria 100 by UTMB 21K
Your race plan, next route workout, official GPX, fueling, cutoff, weather, and calendar link in one place.
I'm preparing for Istria 100 by UTMB 21K. Here is the public training preview.
21.5 km · +157 m · 184 days to race day
Public preview only; my private routes and schedule changes are not included.
Plan: https://trailsplits.com/races/istria-100-by-utmb-21k/training-plan?tier=strong-finish&strength=1&strength_track=no-gym&engine=unified
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Terrain autopilot
Find a matching route near you
We'll look for a loop near you that matches your next run (25 min · ~4 km)
and rehearses the 7 m/km demand of 21K.
Terrain intel
Expect limestone tracks, forest roads, medieval hill-town climbs, and long runnable stretches toward Umag.
Weather & kit
Early April can bring cool nights, wet trails, and mild daytime coastal running.
What this plan focuses on
Build early-season long-run consistency.
Practice night running for the longest route.
Keep climbing work steady rather than overly steep.
Rehearse nutrition on runnable terrain.
Prepare for wet limestone and variable footing.
Unified race plan · beta
Uses the same load, recovery and taper rules as race discovery, with course-specific climbing only because this course has verified elevation.
Use it for race-effort sessions and race day. Easy runs stay easy whatever the goal; the plan's efforts come from how you run now.
Your starting point
Not stated. The plan assumes a typical starting week for this race and opens at 3h 00m of running.
Fit the plan to your recent training
This schedule opens at 3h 00m of running in week one and peaks at 4h 15m in a week; the longest planned outing is 1h 45m. These are prescriptions, not proof of readiness.
Adjust this plan
Swap concrete training days, or mark a day done/skipped without changing the race-specific template.
Calendar subscriptions refresh on the calendar app's schedule. This calendar export uses the selected start date and includes weekly summaries and any pre-base sessions. Use Keep this plan above for a fixed copy of the displayed race schedule.
Route-aware workouts
Key sessions include route buttons that deep-link into the Planner with pre-filled distance
+ elevation filters.
Little downhill to prepare for; general strength still helps.
Peak week target
0 m
4h 15m total training time
Cutoff pressure
Generous cutoff
11.2 min/km average required. At an easy all-day pace the course takes about 2.5 h of the 4 h allowed.
Training emphasis: aerobic cruising speed, cadence control, and late-race leg speed.
Plan summary
The block begins on 2026-12-14, 10 weeks from now.
Duration
16 weeks
Start
2026-12-14
Peak weekly time
4h 15m
Peak weekly vert
0 m
Week 1Base Building
3h 00m ·
0 m vert
Mon · 2026-12-14rest
Rest
Effort: Rest
Rest or gentle mobility.
Tue · 2026-12-15easy
Easy run + strides
25 min · ~4 km
Effort: Easy; strides fast but relaxed
Start with 10 minutes easy. Then 4 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Wed · 2026-12-16easy
Easy run
35 min · ~5.5 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Start with 10 minutes easy. Then 4 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Wed · 2026-12-23easy
Easy run
35 min · ~5.5 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Start with 10 minutes easy. Then 6 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Wed · 2026-12-30easy
Easy run
30 min · ~4.8 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Start with 10 minutes easy. Then 4 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Thu · 2027-01-07easy
Easy run
45 min · ~7.1 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session B: step-downs (slow 3–4s), lunges/sit-to-stand, soleus raises, carries (backpack), dead bug. Quality reps; stop well before failure. Keep the slow step-downs at least a day away from a long run; if this session falls the day before or after one, swap them for core work. In peak weeks, keep it short and easy.
Sat · 2027-01-09long
Long run
1h 05m · ~10.3 km
Effort: Easy
Build relaxed time on feet at conversational effort.
Start with 10 minutes easy. Then 6 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Wed · 2027-01-13easy
Easy run
30 min · ~4.8 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Start with 10 minutes easy. Then 6 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Wed · 2027-01-20easy
Easy run
25 min · ~4 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Tue · 2027-01-26tempo
Threshold intervals
40 min · ~6.7 km
Effort: Comfortably hard
Start with 10 minutes easy. Then 3 x 5 minutes at a comfortably hard effort, with 2 minutes easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Start with 10 minutes easy. Then 4 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Thu · 2027-02-04easy
Easy run
45 min · ~7.1 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session B: step-downs (slow 3–4s), lunges/sit-to-stand, soleus raises, carries (backpack), dead bug. Quality reps; stop well before failure. Keep the slow step-downs at least a day away from a long run; if this session falls the day before or after one, swap them for core work. In peak weeks, keep it short and easy.
Sat · 2027-02-06long
Long run
1h 15m · ~11.9 km
Effort: Easy
Build relaxed time on feet at conversational effort.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Tue · 2027-02-09tempo
Threshold intervals
50 min · ~8.3 km
Effort: Comfortably hard
Start with 10 minutes easy. Then 4 x 5 minutes at a comfortably hard effort, with 2 minutes easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Tue · 2027-02-16tempo
Threshold intervals
45 min · ~7.5 km
Effort: Comfortably hard
Start with 10 minutes easy. Then 3 x 5 minutes at a comfortably hard effort, with 2 minutes easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Tue · 2027-02-23tempo
Threshold intervals
45 min · ~7.5 km
Effort: Comfortably hard
Start with 10 minutes easy. Then 3 x 5 minutes at a comfortably hard effort, with 2 minutes easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Start with 10 minutes easy. Then 6 x 20 seconds relaxed strides, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Wed · 2027-03-03easy
Easy run
35 min · ~5.5 km
Effort: Easy
Conversational aerobic running. Keep easy days easy enough to support the key work.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Tue · 2027-03-09tempo
Half-marathon effort blocks
55 min · ~9.2 km
Effort: Controlled race effort
Start with 10 minutes easy. Then 3 x 8 minutes at controlled race effort, with 2 minutes easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Effort: Moderate: controlled reps, stop 1–2 short of failure
No-gym Session A: Bulgarian split squat, single-leg RDL, step-ups (bench/stairs), calf raises, side plank. Quality reps; stop well before failure. If 10 reps feels easy, add weight (backpack/water) so the last 2 reps feel challenging. In peak weeks, keep it short and easy.
Tue · 2027-03-16tempo
Half-marathon effort blocks
50 min · ~8.3 km
Effort: Controlled race effort
Start with 10 minutes easy. Then 3 x 8 minutes at controlled race effort, with 2 minutes easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Start with 10 minutes easy. Then 3 x 2 minutes at controlled race effort, with 1 minute easy between repeats. Finish with at least 10 minutes easy; any remaining time is easy.
Run the 21.5 km as planned: start controlled and use the fuelling and kit rehearsed in training.
Cutoff check
If your race has a time limit, this estimates the minimum average pace and whether your
target finish time clears the cutoff.
Result
Min pace: 11.2 min/km
Exports
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Disclaimer: this plan is general information, not medical advice. Adjust based on fatigue,
experience, and injury history.
About the Istria 100 by UTMB 21K course
At 21.5 km with 157 m of elevation gain, this is a fast, punchy distance where speed and hill strength both matter. At 7 m of vertical per kilometer, much of the course is runnable — the plan focuses on building your aerobic cruising speed while preparing you for the steeper sections. The official cutoff is 4 hours, so pace management starts from week one.
This training plan adapts the 16-week structure specifically for 21.5 km with 157 m of elevation gain,
scaling weekly volume and vert targets so your body is ready for race-day demands.
Shorter trail races reward aggressive pacing and strong climbing. The plan emphasises quality intensity — hill repeats, tempo efforts, and race-pace sessions — while building enough endurance to finish strong on tired legs.
Training phases for 21K
The current 16-week schedule has these phases for 21.5 km and 157 m of climbing:
Weeks 1–6 — Base Building: Establish consistent aerobic training and introduce course-like terrain gradually.
Weeks 7–11 — Build: Reduce training load while retaining a small amount of familiar intensity.
Weeks 12–14 — Peak Volume: Practise the longest planned outings and race equipment without adding extra sessions.
Week 15 — Taper: Reduce training load while retaining a small amount of familiar intensity.
Week 16 — Race week: Reduce training and follow the race-day plan.
Pacing a runnable course
At 7 m of vertical per kilometer, much of the Istria 100 by UTMB 21K course is runnable.
Training should emphasise aerobic cruising speed — tempo runs on rolling terrain, sustained effort on moderate climbs, and efficient flat-to-uphill transitions.
The biggest risk on a runnable course is starting too fast; practice negative-split long runs to build discipline.