IRONMAN · Thun · 4 Jul 2027
How to train for IRONMAN Switzerland Thun
Thun puts the Swiss Alps on its course page and riders believe the picture. They imagine a pass. They spend a winter learning to hold a steady effort uphill for an hour, and then they meet a bike course whose longest climb lasts nine and a half minutes. The road above this lake rolls. It never towers.
What it does instead is repeat. A Trained rider's pacing plan cuts 180 km into twenty-six separate climbs carrying 1691 m between them, not one of them long, and the lap is ridden twice. After that comes a marathon over the bridges of Thun with 82 m of climbing in it. So the day asks one narrow question, and it asks it again and again: can you take the same ramp two dozen times at the same number, and still run?
By Kian Briel, founder. Analysed by engine 1, updated
What is actually on the road
The organiser's own course files, drawn the way the Event Analyzer draws a member's race.
- Swim3.87 km3 m upCourse file
- Bike180 km1,691 m upCourse file
- Run42.5 km82 m upCourse file
Swim first, one loop of Lake Thun, 3.9 km of it, with 2h20 on the clock. The exit gives you a flat 200m run on asphalt into the transition area on the soccer pitch of the Lachen Stadion, blue bag on the top bar of the rack and red bag underneath, and the mount line sits just outside it near the Gwattstrasse.
Then the lap, which tips upward inside the first three kilometres and keeps finding reasons to. Each circuit climbs in two staircases. The first is a run of short ramps that lifts you around 200 metres above the start, the second is steeper and ends at the high point of the course, roughly 340 metres up. Between them and after them the road is fast and almost level. Of a Trained rider's 6:45:36, 97 minutes go to climbing and 21 to descending. The remaining five hours are flat road. The organiser's intermediate bike cut-offs fall at Belp, then Plötsch, then Hani, after the lap turns back through Thun.
The run is 42.5 km across Thun's bridges and through the town's streets, lapped, and level enough that the engine reads the entire leg as a single segment from the first metre to the last. The organiser's final intermediate cut-off is at the start of the third lap.
Course shape by distance
- Flat 82%
- Climbing 9%
- Descending 8%
The longest stretches
- Bike, flat13.4 km6% of the bike
- Bike, climbing0.78 km1% of the bike
- Run, flat42.5 km100% of the run
Each row is one unbroken stretch of the course that keeps the same shape the whole way. The number is how much of that leg you spend inside it, and it comes out the same whether you are fast or slow.
What this course asks of each leg
Twelve training dimensions scored for each leg against its own course, the way the Event Analyzer scores a member's race.
Endurance, then durability, then the patience to fuel both. Aerobic endurance scores 95 on all three legs here and aerobic durability 93 on the bike, and since the bike is 54 percent of a Trained rider's day, the top five entries in the cross-leg ranking are bike entries without exception. Strength and force climbs to 53 on the bike against 35 on the run, which is what 1691 m buys, and even so it sits twelfth. Fueling resilience reads 85 on every leg. The hills change this course's flavour. They do not change what it is.
Put in hours, the bands say it again. A Trained rider swims 1:21:16, rides 6:45:36 at 159 W and runs 4:17:58, for 12:34:50. The Competitive band comes home in 10:51:11 from 4.15 W/kg at 75 kg and 4:20 /km threshold pace. Of that gap, 54 minutes are on the bike and 39 on the run. None of it is climbing better.
Heat belongs in the plan. The organiser's own record shows a high of 29 C in 2026 and 28 C the year before. The lake read 17 C in 2024, the one edition it was measured. A Trained rider starts the marathon more than eight hours after the gun, which is late enough that the afternoon, not the morning, sets the pace.
- Aerobic endurance95
- Aerobic durability90
- Muscular endurance90
- Fueling resilience85
- Threshold durability80
- Technical skill69
- Threshold capacity55
- High-intensity capacity25
- Strength / force25
- Environmental resilience20
- Anaerobic capacity15
- Sprint power0
Nymiva reads what you can already show, from your own data
Connect your training history and the Focus Lab scores the same twelve dimensions this course demands against where you sit today. The gap between the two is what you train.
- MeasuredFrom your thresholds and testsThreshold power, threshold pace, critical swim speed and field tests you have done. The dimensions they can carry are scored directly.
- EstimatedFrom your training historyConnected activities are read for what they prove: long efforts, late-session fade, repeated hard work, fueling on long days. Each score says how it was read.
- ProxyFrom a stand-in, and named as oneWhere only an indirect signal exists, the score carries the proxy it came from and a lower confidence, never a number dressed as a measurement.
- UnmeasuredHonestly blankA dimension nothing in your data can answer stays unmeasured. It is never a zero, and the plan does not pretend to know it.
Every dimension ends in one word
- Develop the course asks more than you can show
- Maintain close enough to hold at the minimum dose
- Covered nothing to build here
- Unmeasured the course needs it, your data cannot say yet
Training for a course starts with subtraction. The twelve dimensions scored above for Thun get scored a second time on the other side, out of your tested thresholds and whatever history you have connected, each carrying a note on how firm that reading is. Where your side lands under the course's side, you have found a block worth running. Where it does not, you have found something to hold at a maintenance dose and otherwise leave alone. Rank what is left by leg time, and on a day the bike owns 54 percent of, a bike shortfall beats a swim shortfall of the same depth by a distance.
Nobody is reading this page into a profile, so the 28 weeks sketched below cannot know any of that. It takes the flattest assumption available instead, that your shortfalls sit exactly where the demands are biggest, and lays out 5 developmental blocks from it, one lead dimension per sport per block, with the most course-shaped work held back for last. A member's season argues with this one about order and about dose. That argument is the product.
Train the bike to protect the run
Which demands matter most across the whole race. A leg's demand counts for as much of the day as that leg takes, so a score of 85 on the bike outweighs the same score on the swim.
- 01Aerobic enduranceBike leg, 54% of the day95 × 54%51
- 02Aerobic durabilityBike leg, 54% of the day93 × 54%50
- 03Muscular enduranceBike leg, 54% of the day92 × 54%49
The bike takes 54% of the Trained reference band’s day, so its demands carry the most race weight. What the bike leaves in the legs is what the run gets.
Which demand gets a block, and when
The engine freezes one lead focus per sport on every developmental block, holds the rest at maintenance, and verifies before it reprioritises.
An illustration, not your plan. This page has none of your data, so the season below is the engine’s answer to one stated assumption: that your gaps line up with what IRONMAN Switzerland Thun demands. Your own season is built from your history, your thresholds, the days you can train and the races you have entered, and it will differ from this in its priorities, its sessions and its load.
- 01Run aerobic endurance, a development block4 weeks
- 02Bike muscular endurance, a practice block4 weeks
- 03Bike aerobic durability, a practice block6 weeks
- 04Bike aerobic endurance, a development block5 weeks
In the order the allocator places them, general first, most race-like last.
- Week 1PrepPrep
A lead-in week. It develops nothing by design.
- Weeks 2 to 9Foundation 1Closes with a recovery week
- PriorityBike aerobic endurance
- PriorityRun aerobic endurance
- PrioritySwim aerobic endurance
- SupportRun aerobic durability
- SupportBike aerobic durability
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim aerobic durability
- SupportSwim muscular endurance
- SupportBike fueling resilience
- SupportRun fueling resilience
- SupportSwim fueling resilience
- Weeks 10 to 13Foundation 2Closes with a recovery week
- PriorityBike fueling resilience
- PriorityRun fueling resilience
- PrioritySwim fueling resilience
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportRun aerobic durability
- SupportSwim aerobic endurance
- SupportBike aerobic durability
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim aerobic durability
- SupportSwim muscular endurance
- Weeks 14 to 17Foundation 3Closes with a recovery week
- PriorityBike muscular endurance
- PriorityRun muscular endurance
- PrioritySwim aerobic durability
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportRun aerobic durability
- SupportSwim aerobic endurance
- SupportBike aerobic durability
- SupportSwim muscular endurance
- SupportBike fueling resilience
- SupportRun fueling resilience
- SupportSwim fueling resilience
- Weeks 18 to 21Event shaping 1Closes with a recovery week
- PriorityRun aerobic durability
- PriorityBike aerobic durability
- PrioritySwim muscular endurance
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim aerobic durability
- SupportBike fueling resilience
- SupportRun fueling resilience
- SupportSwim fueling resilience
- Weeks 22 to 25Event shaping 2Closes with a recovery week
- PriorityBike aerobic endurance
- PriorityRun aerobic endurance
- PrioritySwim aerobic endurance
- SupportRun aerobic durability
- SupportBike aerobic durability
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim aerobic durability
- SupportSwim muscular endurance
- SupportBike fueling resilience
- SupportRun fueling resilience
- SupportSwim fueling resilience
- Weeks 26 to 27PeakPeak
The taper. Load comes down toward the race, content stays specific.
- Week 28RaceRace
Race week.
Held at maintenance between blocks
- Runaerobic endurance, aerobic durability, threshold durability, muscular endurance, technical skill, fueling resilience
- Bikemuscular endurance, aerobic durability, aerobic endurance, threshold durability, fueling resilience
- Swimaerobic endurance, aerobic durability, threshold durability, muscular endurance, technical skill, fueling resilience
Touches scheduled by each capability’s own decay, at a fraction of its development dose, so earlier work is still there on race day.
The sessions the blocks are built from
One entry per kind of work the block trains, at the intensity that work is meant to be done at. Where the same work runs at several lengths, the entry shows the span it grows across rather than one entry per length.
- Foundation 1 · Weeks 2 to 975 to 240 min
150 to 210 min at Zone 2
BikePower, Zone 2Trains aerobic capacity - Foundation 1 · Weeks 2 to 940 to 270 min
180 to 210 min at Zone 3, then 30 min at Zone 4
BikePower, Zone 3Trains aerobic capacity - Foundation 1 · Weeks 2 to 935 to 120 min
90 min at Zone 2
RunPace, Zone 2Trains aerobic capacity - Foundation 1 · Weeks 2 to 950 min
4 x 1.5 min at Zone 3, 6 min easy between
RunHeart rate, Zone 3Trains aerobic capacity - Foundation 1 · Weeks 2 to 945 to 51 min
4 x 8 min at Zone 2, 1 min easy between
SwimPace, Zone 2Trains aerobic capacity - Foundation 1 · Weeks 2 to 947 to 81 min
3 x 1000 m at Zone 3, 0.3 min easy between
SwimPace, Zone 3Trains aerobic capacity
12× climb-to-false-flat repeats
2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, then 2 min at Zone 5, then 3.5 min at Zone 4, 0.5 min easy between
Compiled by the deterministic course compiler from the organiser’s file: the course’s one repeatable requirement, rehearsed at a dose the progression allows.
- Bike
- 97 min
- Trains muscular endurance
- Supports strength force
- Supports high intensity capacity
- Supports threshold durability
28 weeks, laid out backwards from race day
The shortest runway Nymiva builds for this event type, with its blocks, recovery weeks, taper and race week in place.
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- Prep
- Foundation
- Event shaping
- Peak
- Race
- Recovery week
Your own season carries these same phases on your own dates, with the load solved from your fitness and the days you can train, and it changes when your data does.
What each level does on the day
Reference finish times per peer band, the pacing plan the model holds each band to, and where the day is decided.
| Band | Swim | Bike | Run | Finish |
|---|---|---|---|---|
| Recreational2:11 /100m critical swim speed · 2.47 W/kg at 75 kg · 6:08 /km threshold pace | 1:35:55 | 7:32:01 | 5:10:14 | 14:28:10 |
| Trained1:51 /100m critical swim speed · 3.03 W/kg at 75 kg · 5:06 /km threshold pace | 1:21:16 | 6:45:36 | 4:17:58 | 12:34:50 |
| Competitive1:36 /100m critical swim speed · 4.15 W/kg at 75 kg · 4:20 /km threshold pace | 1:10:17 | 5:51:43 | 3:39:11 | 10:51:11 |
| Elite1:26 /100m critical swim speed · 5.27 W/kg at 75 kg · 3:50 /km threshold pace | 1:02:58 | 5:20:54 | 3:13:54 | 9:47:46 |
Pacing plan
- 0 km0.1%28.7 km/h5:43
- 2.73 km4.3%12.8 km/h4:20
- 3.66 km0.4%27.2 km/h3:07
- 5.07 km4.7%12 km/h4:44
- 6.01 km-0.5%31.8 km/h19:34
- 16.4 km5.1%11.3 km/h3:03
- 17 km-4.1%49.4 km/h1:17
- 18 km2.2%19 km/h1:18
76 more segments in the full plan.
- Run: reach 4:20 /km and this course gives back 1:43:39.
Where it is decided
Above the lake, against a clock nobody shows you.
You climb for 97 minutes out there and descend for 21. That ratio is the entire argument. The road spends an hour and a half lifting you and takes it back in a third of the time, so a minute overspent on a ramp is a minute that never comes home to you at nearly 60 km/h on the other side. The last of the steep ones is the one to fear: 783 m at 6.8 percent at kilometre 152, where a Trained rider moves slower than at any other moment of the day, five hours deep with a marathon waiting.
Look at the session the engine compiled from this bike file and the shape gives the course away. Twelve repeats of two minutes climbing run straight into three and a half minutes of what it names the false-flat continuation. The road does not hand back the descent at the top. It keeps tilting gently upward for a few minutes more, and that is precisely where a rider who answered the ramp with a surge finds out. The longest unbroken stretch on the lap follows, 13.4 km from kilometre 73, and it is the largest single block of time the bike leg contains. That is the recovery on offer. Take it.
Getting it wrong
The first mistake is the winter before. Riders who read the word Alps go and train hour-long climbs, and they arrive able to do something this course never requests. Holding one steady number through two dozen interruptions is a different capability entirely, and it is built by a different block.
Second, the opening lap. You reach the turn back through Thun with good legs, the day's steepest pitch still in front of you, and every reason to trust your split. A course ridden twice publishes your arithmetic at halfway. If lap one cost more than you meant it to, lap two will cost more than that, and the run will settle the account.
Third, the clock, which here is not a formality. The organiser allows 10h30 for the swim, the first transition and the bike, and 17h00 for the day. In these bands a Recreational rider swims 1:35:55 and rides 7:32:01, landing inside the bike cut-off with a little over an hour spare and no more. Twenty minutes lost to a puncture above Plötsch eats most of that. The cut-offs at Belp, at Plötsch and at Hani are the organiser saying where it gets counted, and the one at the start of the third lap of the run is saying it for the last time.
Conditions on the day
- 2026high 29 C, low 10 C
- 2025high 28 C, low 16 C
- 2024high 25 C, low 11 Cwater 17 C
From the organiser’s own records. Not a forecast.
Every session is a claim, every block is a test
A plan is not a calendar. Each key session states what it trains and how that is checked, and each block ends with a public verdict before the next one is chosen.
What a block promises
Bike aerobic endurance moves from your baseline to a stated target by the end of Foundation 1
- The baseline is your measured score when the block starts. The target is the score the model predicts for it.
- Verified at the block’s recovery week, by a field test or a refresh of the supply read from your history.
- Confidence rises by agreement between independent signals, never by one metric crossing a line.
- A block that misses its target is a public miss. The next block is chosen from what was proven, not from what was planned.
- 01Stimulus achievedThe work landed in the zone the session named, for the dose it named.
- 02Partially achievedSome of the work landed. The session banks what it can prove.
- 03Not achievedThe load may have been there. The stimulus was not, so nothing is banked.
- 04Data insufficientNo usable stream. The session is neither credited nor blamed.
- Session verified
- Progression banked
- Block verified
- Priority reassessed
- Plan adapted
Your numbers, this course
Analyze IRONMAN Switzerland Thun against my fitness
The same simulation and the same Focus Lab read, on your thresholds instead of a band’s. Three numbers give a finish estimate and a partial read. A connected history gives the whole table.
The first 14 days are free.
- Trained band finish
- 12:34:50
- Of the day on the bike
- 54%
- Dimensions scored per leg
- 12
- Season runway shown
- 28 wk
Questions people ask
- How hilly is the IRONMAN Switzerland Thun bike course?
- Hilly, but never for long. The 180.2 km course holds 1691 m of climbing and the pacing plan breaks it into twenty-six separate climbs. The longest takes a Trained rider nine and a half minutes, the steepest is 783 m at 6.8 percent, and the whole lap is ridden twice.
- What are the cut-off times at IRONMAN Switzerland Thun?
- The organiser publishes 2h20 for the swim, 10h30 for the swim, first transition and bike together, and 17h00 for the whole day. Intermediate cut-offs sit on the bike at Belp, at Plötsch and at Hani, with one more on the run at the start of the third lap.
- What water temperature should I expect in Lake Thun?
- The organiser recorded 17 C in 2024 and published no water reading for 2025 or 2026. Air temperatures over those three editions ran to a high of 29 C and down to a low of 10 C.
- How long is the season on this page?
- The illustrative season runs 28 weeks with five developmental blocks and a two-week taper. Your own season starts from your own numbers and can be longer than this one.
Course data from the organiser’s published files, analysed 23 Sept 2026 by engine 1, demand model 4. Reference times are simulated for a peer band at a stated reference athlete and are not a prediction for anyone. Nothing on this page is medical advice.
IRONMAN® and IRONMAN 70.3® are registered trademarks of World Triathlon Corporation. Nymiva is an independent training platform and is not affiliated with, sponsored by or endorsed by World Triathlon Corporation. Course data is read from the organiser’s public course pages for the purpose of describing the event.