IRONMAN 70.3 · Hoorn · 20 Jun 2027
How to train for IRONMAN 70.3 Westfriesland
Fast and flat, ideal for first-timers and for personal bests: that is how the organiser sells Westfriesland, and for once the file backs the brochure. A bike of 91.4 km climbs 82 m. The run climbs 29 m. The engine reads 99.8 percent of the whole course as flat by distance. People take that as a promise that the course will carry them.
It will not. A course with no hills is also a course with no rest, and nothing on the roads around Hoorn tells you when to back off. A Trained athlete's 5:45:58 is not decided by terrain. It is decided by whether one number holds from the edge of town to the dismount line.
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.
- Swim1.9 km0 m upCourse file
- Bike91.4 km82 m upCourse file
- Run21.2 km29 m upCourse file
The swim is a single loop of 1.9 km in the old harbour of Hoorn, in water the organiser logged at 22 C in 2026 and 19 C two years earlier. A short exit leads to one transition on the football pitch in Hollandia Park, 200 m of carpet from the water, then flat, short grass.
The bike is one loop of 91.4 km from the city centre into the countryside, among windmills, polders and dykes, through small towns and back. The run is one loop of 21.2 km through the historic centre, past monumental buildings and the docks, to the finish at the Stadsstrand.
Now the profile, because there is barely one. The engine finds a single gradient on the whole bike worth naming, a drop of 193 m at 3.1 percent near kilometre 19. It splits the ride into two flat stretches either side of that drop. The first holds 20.8 percent of the bike leg. The second holds 79.4 percent. The run is one flat segment from the first metre to the last.
Course shape by distance
- Flat 100%
- Climbing 0%
- Descending 0%
The longest stretches
- Bike, flat18.9 km21% of the bike
- Bike, flat72.3 km79% of the bike
- Run, flat21.2 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.
Aerobic endurance and muscular endurance, in that order, on every leg. The demand model scores them 85 and 80 on each of the three legs, with threshold capacity at 70 and both durability scores at 65 behind them. Because the bike fills 51 percent of a Trained athlete's race, the five largest demands on the course all belong to it.
The low scores tell the story just as well. High-intensity capacity reads 40 on the bike and strength and force 35. On a rolling half-distance those numbers rise, because every ramp demands a minute above your steady power. Westfriesland has no ramps. Ask the engine to build a session from this bike file and it hands back one block of work: an hour at threshold without a break, a warm-up before it and an easy spin after. There are no repeats in it because the road offers none.
Put the bands beside that. A Trained athlete swims 38:08, rides 2:57:30 at 182 W and runs 2:00:20, for 5:45:58. The Competitive band finishes in 5:02:14 from 4.15 W/kg at 75 kg, twenty minutes faster on the bike and eighteen on the run. No climb separates those two athletes. Every minute between them is bought by a higher number held without interruption, and by a run that starts on legs the bike never overdrew.
Heat is not the test here. The organiser logged highs of 23 C in 2026 and 22 C in 2025, and in 2024 the low was 9 C. The engine scores environmental resilience at 10 on every leg.
- Aerobic endurance85
- Muscular endurance80
- Threshold capacity70
- Aerobic durability65
- Threshold durability65
- Technical skill61
- Fueling resilience55
- High-intensity capacity40
- Anaerobic capacity25
- Strength / force20
- Environmental resilience10
- Sprint power5
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
Nymiva reads the same twelve dimensions from both ends. The course side comes from the organiser's files. The athlete side comes from thresholds and connected training history, with a note on every score saying what it was read from and how far to trust it. A dimension counts as a gap only where the course asks more than the athlete can show, and each gap is weighted by the share of the day it fills. With the bike at more than half of a Trained athlete's race and the swim at about a ninth, a bike gap here outweighs a swim gap of equal size several times over.
No athlete stands behind this page, so its season cannot see anyone's gaps. It makes the plainest assumption, that they sit where the demands are largest, and lays out 24 weeks in 5 developmental blocks closed by a two-week taper. Aerobic endurance leads the opening block in all three sports. Aerobic durability takes the second block. Threshold capacity leads the third and muscular endurance the fourth, before aerobic endurance returns to lead the last block ahead of the taper. A member's season is built from their own numbers and will argue with this one.
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, 51% of the day85 × 51%44
- 02Muscular enduranceBike leg, 51% of the day80 × 51%41
- 03Threshold capacityBike leg, 51% of the day70 × 51%36
The bike takes 51% 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 70.3 Westfriesland 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 muscular endurance, a practice block4 weeks
- 02Run aerobic endurance, a development block4 weeks
- 03Bike muscular endurance, a practice block4 weeks
- 04Bike aerobic endurance, a development block4 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 5Foundation 1Closes with a recovery week
- PriorityBike aerobic endurance
- PriorityRun aerobic endurance
- PrioritySwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim muscular endurance
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportBike aerobic durability
- SupportRun aerobic durability
- SupportSwim aerobic durability
- Weeks 6 to 9Foundation 2Closes with a recovery week
- PriorityBike aerobic durability
- PriorityRun aerobic durability
- PrioritySwim aerobic durability
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim muscular endurance
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- Weeks 10 to 13Foundation 3Closes with a recovery week
- PriorityBike threshold capacity
- PriorityRun threshold capacity
- PrioritySwim threshold capacity
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim muscular endurance
- SupportBike aerobic durability
- SupportRun aerobic durability
- SupportSwim aerobic durability
- Weeks 14 to 17Event shaping 1Closes with a recovery week
- PriorityBike muscular endurance
- PriorityRun muscular endurance
- PrioritySwim muscular endurance
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportBike aerobic durability
- SupportRun aerobic durability
- SupportSwim aerobic durability
- Weeks 18 to 21Event shaping 2Closes with a recovery week
- PriorityBike aerobic endurance
- PriorityRun aerobic endurance
- PrioritySwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim muscular endurance
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportBike aerobic durability
- SupportRun aerobic durability
- SupportSwim aerobic durability
- Weeks 22 to 23PeakPeak
The taper. Load comes down toward the race, content stays specific.
- Week 24RaceRace
Race week.
Held at maintenance between blocks
- Runmuscular endurance, aerobic endurance, aerobic durability, threshold capacity, threshold durability
- Bikemuscular endurance, aerobic endurance, aerobic durability, threshold capacity, threshold durability
- Swimaerobic endurance, aerobic durability, threshold capacity, threshold durability, muscular endurance, technical skill
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 575 to 240 min
150 to 210 min at Zone 2
BikePower, Zone 2Trains aerobic capacity - Foundation 1 · Weeks 2 to 540 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 535 to 120 min
90 min at Zone 2
RunPace, Zone 2Trains aerobic capacity - Foundation 1 · Weeks 2 to 550 min
4 x 1.5 min at Zone 3, 6 min easy between
RunHeart rate, Zone 3Trains aerobic capacity - Foundation 1 · Weeks 2 to 545 to 51 min
4 x 8 min at Zone 2, 1 min easy between
SwimPace, Zone 2Trains aerobic capacity - Foundation 1 · Weeks 2 to 547 to 81 min
3 x 1000 m at Zone 3, 0.3 min easy between
SwimPace, Zone 3Trains aerobic capacity
Sustained course race pressure
60 min at Zone 4
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
- 85 min
- Trains threshold durability
- Supports aerobic durability
24 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.
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
- 23
- 24
- 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 | 0:45:00 | 3:12:40 | 2:24:43 | 6:32:23 |
| Trained1:51 /100m critical swim speed · 3.03 W/kg at 75 kg · 5:06 /km threshold pace | 0:38:08 | 2:57:30 | 2:00:20 | 5:45:58 |
| Competitive1:36 /100m critical swim speed · 4.15 W/kg at 75 kg · 4:20 /km threshold pace | 0:32:58 | 2:37:01 | 1:42:15 | 5:02:14 |
| Elite1:26 /100m critical swim speed · 5.27 W/kg at 75 kg · 3:50 /km threshold pace | 0:29:32 | 2:23:24 | 1:30:27 | 4:33:23 |
Pacing plan
- 0 km0%30.8 km/h36:54
- 18.9 km-3.1%45.8 km/h0:15
- 19.1 km0%30.8 km/h2:20:48
- Run: reach 4:20 /km and this course gives back 43:44.
Where it is decided
After kilometre 19, on the long flat run home that holds 79.4 percent of the bike leg.
Before the drop the field is still bunched, the legs are fresh from the harbour, and there is plenty to look at. After it there is nothing to react to. No climb to meter the effort against, no descent to recover on. Just one question, put without pause: can you hold 182 W the whole way home, without creeping up when you feel strong or sagging when your attention wanders?
Both directions cost time on a road this flat. The rider who drifts a little over plan feels nothing, because there is no hill to make it hurt, and pays for it later. The rider whose concentration fades gives minutes away and never notices the moment it happened. The steady rider is rarely the fastest out of town and nearly always the fastest off the bike.
Then the run reads the verdict. 21.2 km in one loop, 29 m of climbing, one flat segment. A Trained athlete covers it in 2:00:20 from an input of 5:06 /km threshold pace. On flat ground a spent runner has no hill to blame and no descent to hide on. The pace simply falls away, one kilometre after another, past the docks and on toward the Stadsstrand.
Getting it wrong
The first mistake is reading flat as easy. Riders prepare with long rides broken up by stops and hills, and arrive never having held a single unbroken hour at race effort. That hour is exactly what the course session asks for, and it is what the bike is made of.
The second happens in the first 19 km. That stretch holds 20.8 percent of the bike leg and comes straight after a harbour swim and a short dash across the grass, with the field packed and the road dead flat. It feels free. Whatever number you set there, the remaining 72 km inherit it.
The third is the run's single loop. There is no second lap on which to notice you started too fast, and no familiar corner to check your pace against. Every kilometre through the old centre is new road. Run the opening kilometres at the pace you planned, and let the Stadsstrand come to you.
Conditions on the day
- 2026high 23 C, low 18 Cwater 22 C
- 2025high 22 C, low 15 Cwater 23 C
- 2024high 18 C, low 9 Cwater 19 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 70.3 Westfriesland 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
- 5:45:58
- Of the day on the bike
- 51%
- Dimensions scored per leg
- 12
- Season runway shown
- 24 wk
Questions people ask
- How flat is the IRONMAN 70.3 Westfriesland bike course?
- As flat as the organiser says. The one-loop bike file measures 82 m of climbing over 91.4 km, and the only gradient the profile shows is a drop of 193 m at 3.1 percent near kilometre 19. Everything else reads as flat road.
- What water temperature should I expect in the old harbour of Hoorn?
- The organiser logged 22 C in 2026, 23 C in 2025 and 19 C in 2024. The wetsuit decision is not on the organiser's course page, so check it in race week.
- Where does the IRONMAN 70.3 Westfriesland run go?
- One loop of 21.1 km through the historic centre of Hoorn, past monumental buildings and the docks, finishing at the Stadsstrand. The file climbs 29 m in total and the engine reads it as one flat segment.
- How long is the season on this page?
- The illustrative season runs 24 weeks, with five developmental blocks and a two-week taper. It is built from the course alone. A member's season starts from their own numbers and can be longer.
Course data from the organiser’s published files, analysed 25 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, and 5150 is a trademark, 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.