So you’ve conquered the half marathon. Maybe even the full. Now you’re eyeing something longer — but 100 kilometers sounds… like a lot.
Welcome to the world of sub-ultra marathons: races between 25K and 50K that challenge your endurance without wrecking your life. These events are ideal for runners who want to explore new distances, tackle hills and trails, or prepare for full ultramarathons — without committing to months of volume and logistics.
But don’t mistake “shorter than an ultra” for “easier than a marathon.” Sub-ultra races bring their own unique demands: longer time on feet, terrain variability, fueling precision, and a completely different pacing mindset.
This guide is here to walk (and run) you through:
How long your training should last
What your weekly structure should look like
How to handle fueling, terrain, and mindset shifts
Sample workouts for both 30K and 50K distances
🧭 Whether you’re a marathoner looking for a new thrill, or a trail runner going long for the first time — you’re in the right place.
Sub-ultra training isn’t just “marathon training plus 5K.” It’s a shift in approach.
📏 Distances
30K (18.6 miles) → often on roads, fast runners finish in ~2 hrs
50K (31.1 miles) → usually trail-based, average times = 5–8 hrs
🔁 The Key Differences from Marathon Training
Aspect
Marathon Plan
Sub-Ultra Plan
Focus
Pace & finish time
Time-on-feet & effort
Fueling
Gels, minimal intake
Sustained fueling practice
Terrain
Road/predictable
Often trail/elevation
Long Runs
Max ~32–35K
May go by hours, not KM
Recovery
Fewer back-to-backs
Possible weekend doubles
🧠 Effort Over Pace
Especially on trails, pace becomes meaningless. Hills, terrain, temperature, and altitude can swing pace by minutes/km. Instead:
Train by effort level (RPE)
Use heart rate as a rough guide
Track total time on feet
💡 Pro Tip:
Your weekly mileage might be lower than in marathon training — but your training load (duration, elevation, recovery demand) is higher.
🟩 3. How Many Weeks Do You Need?
Training for a sub-ultra marathon isn’t just about finishing — it’s about arriving confident, uninjured, and prepared.
The duration of your training plan depends on two key factors:
🧱 Your current fitness level
🎯 Your target race distance and terrain
📅 Recommended Training Durations
Race Distance
Terrain
Training Time
30K
Road
8–12 weeks
30K
Trail
10–14 weeks
50K
Rolling
12–16 weeks
50K
Mountain
14–18+ weeks
🧠 Trail races require more prep — not just for fitness, but for terrain handling, gear testing, and fueling practice.
🏁 Can You Start Training Now?
Here’s a quick readiness checklist:
✅ You run 3x per week consistently ✅ Your long run is at least 12–15 km ✅ You can jog easy for 90 minutes without major issues ✅ You’ve done some hills or cross-training ✅ You have 8–18 weeks until race day
If that sounds like you — you’re ready to begin.
🏗️ If not, spend 4–6 weeks building a base first.
🔄 What If You’re Coming from a Marathon Plan?
Great! But remember:
Sub-ultras (especially trail 50Ks) may demand slower, longer runs
Less emphasis on pace, more on elevation and duration
You’ll likely add back-to-back runs or trail-specific workouts
🟩 4. Weekly Structure for Sub-Ultra Training
Consistency beats intensity. A good sub-ultra training week builds aerobic endurance, trains fueling, and improves strength — without burning you out.
“If you don’t have time to run long, run often. But if you only have time for one workout — make it your long run.”
🟩 5. Long Runs: Your Most Important Workout
No matter what distance you’re training for — the long run is the centerpiece of your week. It builds endurance, mental toughness, fueling habits, and prepares your body for race-day demands.
But how long is “long”? It depends on whether you’re training for time or distance — and whether you’re running on road or trail.
⏱️ Time-Based vs Distance-Based
Use This If…
Long Run Based On…
Trail or elevation race
⏱️ Time (hours)
Flat road race (30K)
📏 Distance (km)
📅 Suggested Long Run Progressions
🛣️ 30K Road Race Plan (Distance Focus)
Week 1: 16 km
Week 3: 20 km
Week 5: 24 km
Peak: 26–28 km (2–3 weeks before race)
🥾 50K Trail Race Plan (Time Focus)
Week 1: 90 min
Week 3: 2 hr
Week 6: 2.5–3 hr
Week 10+: up to 4 hr (hiking OK)
Peak: ~4:30 hr (with terrain)
🧭 You don’t need to “run” 50K in training. You need to train your body for being on your feet for hours — fueled, focused, and functional.
🍌 Fueling During Long Runs
Sub-ultra = sub-marathon fueling rules don’t apply. Start early. Fuel often. Practice your exact race-day nutrition.
Learn to problem-solve (blisters, cramps, gear issues)
💬 Boss Tip:
“You don’t build speed in your long run — you build durability.”
🟩 6. Back-to-Back vs Tempo Runs
Every sub-ultra runner needs to train both their aerobic engine and their race-specific fatigue resistance. But how you do that depends on your race type, terrain, and current strengths.
The two most effective approaches? ➡️ Back-to-back runs ➡️ Tempo sessions
Let’s break it down.
🔁 Back-to-Back Runs (Sat + Sun)
What it is: Two long-ish runs on consecutive days to simulate multi-hour fatigue.
Why it works:
Prepares you for running tired, especially for 50K+ trail events
Builds muscular and mental resilience
Less risky than a single monster long run
When to use:
Preparing for trail or hilly 50Ks
No time for a full 4-hr session
Want to build volume safely
Example:
Sat: 3 hr trail run
Sun: 1.5 hr easy jog/hike
Caution: Don’t do more than 2–3 weekends of back-to-backs without recovery weeks.
🟨 Tempo Runs
What it is: Sustained efforts at “comfortably hard” pace (Zone 3–4 / RPE 6–7)
🧪 The best runners mix both — but don’t try to do everything every week.
🟩 7. Simulating Race Terrain
You can’t fake terrain. You can run 30 kilometers on flat roads every week, but if your race has 1,200 meters of elevation, rocks, roots, and steep descents — you’re gonna feel it.
🧭 To train smart, train where you’ll race — or as close to it as possible.
🏔️ Trail Race? You Need Trail Time
Even if you live in a city, try to get on dirt at least 1–2 times per week. It trains:
Stabilizer muscles
Footwork and balance
Hiking form on climbs
Confidence on descents
If your race is:
Technical → practice rocky terrain
Rolling → simulate short steep climbs
High elevation → do treadmill incline or stair sessions
🧗♀️ Simulate Climbing (Even in the City)
If you don’t have mountains nearby:
🏃♂️ Hill repeats (parking garages, bridges, treadmills)
⏱️ Power hiking practice (Zone 2–3 effort)
🪜 Stair climbing workouts
🎒 Weighted pack hikes for extra strength
💬 “No trail? No problem — simulate the effect, not just the surface.”
🧎♂️ Practice Technical Descents
Downhills destroy quads. If your race includes steep or loose terrain, do:
Controlled downhill strides
Eccentric strength work (lunges, step-downs)
Fast descents on runnable trails to build rhythm
🔁 Sample Simulation Workouts
Trail Day:
90 min on rolling dirt paths
Include 3–4 moderate climbs (3–6 min each)
Run the downhills with control but speed
Urban Simulation:
10 × 1-minute hill sprints + jog back
15 min continuous stairs
20-min treadmill @ 8–10% incline
🔧 Pro Tip: Build “Elevation Endurance” Gradually
Start with 50–100m gain per 10K run
Work up to 600–1200m gain per long run for trail 50K
Keep effort zones low during steep hikes (Zone 2–3)
🧠 The goal isn’t just vertical — it’s teaching your body how to move efficiently over vertical.
🟩 8. Fueling and Hydration in Training
You can’t outrun a bonk — but you can train to prevent one.
Sub-ultra distances (30K–50K) sit in the fueling danger zone: long enough to deplete your glycogen, short enough to make you think you don’t need to eat.
🍌 Don’t wait for race day to experiment — practice fueling early and often during training.
🍽️ How Much Should You Eat?
✅ General Guideline:
150–250 kcal per hour
Start at 30–40 minutes into the run
Eat every 20–30 minutes
🥤 Fluids:
400–750 ml/hour (13–25 oz)
Add electrolytes or salt tabs if run is over 90 min or weather is hot
⚡ Fuel Types:
Option
Pros
Caution
Gels
Portable, fast energy
Can upset stomach
Chews/gummies
Easy to pace intake
May need water to digest
Bananas
Natural, gentle carbs
Bulky and perishable
Dates/figs
High sugar + potassium
Sticky, heavy
Bars
Higher kcal per bite
Harder to chew while running
🧪 Train Your Gut (Like a Muscle)
Fueling isn’t just nutrition — it’s a physiological skill. You must teach your gut to absorb fuel under stress.
Start with low doses (e.g. 100 kcal/hr)
Build up to race-day targets
Alternate carb types (glucose + fructose)
Hydrate consistently, not reactively
🧠 If you never fuel during training, your stomach won’t cooperate on race day.
If it’s not in your stomach by halfway — it won’t save you later.
🟩 9. Mindset: You’re Training for Time on Feet
Sub-ultra races aren’t about speed — they’re about staying strong, smart, and steady for hours.
Unlike a 10K or even a road marathon, your goal isn’t just to run fast, but to stay functional from start to finish. Especially on trails, where conditions change, you may climb for 30 minutes and descend for 15 — pace becomes irrelevant.
That’s why training your mindset is just as important as your muscles.
⌛ Time-on-Feet = The True Metric
Don’t obsess over pace charts.
6:00/km on roads might be 9:00/km on trails
A 3-hour trail run may cover fewer kilometers — but more elevation, fatigue, skill
What matters is how long you’re moving, not how far.
🧭 You’re not chasing pace — you’re building resilience.
🧘♂️ Train Mental Habits, Too
Use training runs to practice:
Walk breaks with intention (uphill hikes ≠ weakness)
Pacing based on breath/RPE (rate of perceived exertion)
You don’t need to run 100 miles to challenge yourself — sometimes 30 to 50 kilometers is more than enough.
Training for a sub-ultra marathon is a unique opportunity to step into endurance, explore your limits, and experience long-distance running without overcommitting your life. With the right structure, patience, and fueling plan, you can go from “I’ve never run more than a half marathon” to “I finished a 50K!”
🧭 Key Takeaways:
Train for time-on-feet, not just pace
Use long runs and terrain simulation to mimic race conditions
Prioritize fueling and recovery as part of your training
Mindset matters — you’re not trying to win, you’re trying to not break
💬 The race starts when your legs want to quit — and you keep going anyway.
How long should I train for a 50K trail race?
Most runners need 14–18 weeks to build endurance, terrain handling, and fueling habits for a 50K.
Can I finish a 30K race without doing a marathon first?
Absolutely. Many runners successfully complete 30K races as their first endurance event beyond the half marathon.
What’s the difference between sub-ultra and marathon training?
Sub-ultra plans focus more on time-on-feet, terrain simulation, fueling, and recovery — not just pace.
Do I need to run back-to-back long runs?
Only for 50K trail races or if you lack time for single long sessions. They’re optional but powerful.
Should I practice walking during training?
Yes. Strategic walk breaks (especially uphill) are common in sub-ultra events and help preserve energy.
What shoes are best for sub-ultra trail races?
Lightweight trail shoes with moderate grip and cushioning — think: Altra, Hoka, Salomon, or Topo.
How often should I fuel during training runs?
For runs longer than 60 minutes, fuel every 30–45 minutes with 150–250 kcal/hour.
Is heart rate or pace better for training?
Use heart rate or effort (RPE) as your guide — pace is unreliable on trails or in heat/elevation.
How many kilometers per week do I need to run?
For 30K: ~35–50 km/week. For 50K: ~55–75 km/week at peak. It varies by experience and terrain.
Can I finish a 50K without running that distance in training?
Yes. Most runners peak at 4–4.5 hour long runs. You don’t need to run the full race distance beforehand.
About the Author Lost Pace is an ultramarathon runner, shoe-tester and the founder of umit.net. Based year-round in Türkiye’s rugged Kaçkar Mountains, he has logged 10,000 + km of technical trail running and completed multiple 50 K–100 K ultras.
Blending mountain grit with data, Lost analyses power (CP 300 W), HRV and nutrition to craft evidence-backed training plans. He has co-written 260 + long-form guides on footwear science, recovery and endurance nutrition, and is a regular beta-tester of AI-driven coaching tools.
When he isn’t chasing PRs or testing midsoles, you’ll find him sharing peer-reviewed research in plain English to help runners train smarter, stay healthier and finish stronger.
Ultrarunner · Data geek · Vegan athlete
