IRONMAN 70.3 · Boise · 24 Jul 2027
How to train for IRONMAN 70.3 Boise
The organiser's summary of Boise has three words in it. Reservoir, hilly, flat. The middle one is the one people train for. They ride hills all spring, arrive in the capital of Idaho with climbing legs, and then spend most of the bike on flat road and the whole run in a heat they never prepared for.
Look at the file and at the weather record. The bike climbs 519 m and descends 633 m, and the steepest ramp on it is 355 m long. The organiser logged a high of 42 C in 2024. This year it was 39 C. Boise is not a climbing race. It is a heat race with a few climbs early in the ride.
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.
- Swim1.96 km1 m upCourse file
- Bike90 km519 m upCourse file
- Run21 km in 2 laps41 m upCourse file
The swim is one lap of Lucky Peak Reservoir. It starts and finishes at Barclay Bay, in water the organiser calls calm and clear. It was 19 C in 2025.
The bike leaves the reservoir on a sweeping downhill, 1.4 km at 5 percent in the file, then rolls through rural Boise roads and neighbourhood streets to Transition 2 downtown. It is a point-to-point ride, and it finishes lower than it starts, which is why it descends more than it climbs. The climbing comes in two clusters. The first sits between 7 km and 26 km. It opens with 696 m at 4.3 percent and a shorter ramp after it. Then comes the longest climb of the day, 1.35 km at 5.1 percent, and soon after it the steepest, 355 m at 6.5 percent. The second comes at 65 km, a short 4.9 percent ramp and then 779 m at 3.3 percent, before a descent of 1.6 km at 4.8 percent.
The run is 21 km in two loops on the Boise River Greenbelt Trail, finishing in downtown Boise. It climbs 41 m in total. The engine reads it as one flat segment from start to finish.
The profile, taken whole, is 92.1 percent flat by distance. The single longest stretch on the bike runs from 25.9 km to 54.3 km, just after the steepest climb, and holds 30 percent of the leg. The steepest climb itself holds 1.3 percent.
Course shape by distance
- Flat 92%
- Climbing 3%
- Descending 5%
The longest stretches
- Bike, climbing0.36 km1% of the bike
- Bike, flat28.4 km30% of the bike
- Run, flat21 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.
Heat, before anything the terrain asks. The demand model scores environmental resilience at 90 on every leg, and on the bike, which fills more than half of the day, that is the largest weighted demand on the course. The run's 90 ranks seventh across the race, above every other run demand.
Then the usual half-distance pair. Aerobic endurance reads 85 on all three legs, muscular endurance 81 on the bike and 80 on the run and in the water. Where Boise differs from a flat course is lower down the list. High-intensity capacity reads 50 on the bike against 40 on the run, and strength and force reads 46 on the bike against 30. That difference is the climbing. Both scores are real, and they rank eleventh and twelfth across the race, behind every aerobic demand the bike makes. Technical skill in the swim reads 76.
In the bands, a Trained athlete swims 39:19, rides 3:03:15 at 182 W and runs 1:59:08, for 5:51:42. Of that bike, the climbs take about 17 minutes and the flat road about two hours and 37. The Competitive band finishes in 5:07:20 from 4.15 W/kg at 75 kg, about 21 minutes faster on the bike and 18 on the run. For the Trained athlete, the run starts close to four hours into the day.
- Environmental resilience90
- Aerobic endurance85
- Muscular endurance80
- Technical skill76
- Threshold capacity70
- Aerobic durability65
- Threshold durability65
- Fueling resilience55
- High-intensity capacity40
- Anaerobic capacity25
- Strength / force20
- 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 scores the same twelve dimensions on both sides. The course is read from its file and the organiser's conditions. The athlete is read from their thresholds and their connected training history, with a note on every score saying what it came from and how far to trust it. A gap exists only where the course asks for more than the athlete can show, and each gap is weighted by how much of the day it fills, which is why a bike gap here counts for more than four times a swim gap of the same size.
No athlete stands behind this page, so the season beneath it cannot know anyone's gaps. It takes the plainest case, that they sit where the demands are largest, and lays out 24 weeks in 5 developmental blocks with a two-week taper. Aerobic endurance leads the first block in every sport. Aerobic durability leads the second on the bike and the run while the swim works threshold capacity. The third turns the bike and run to threshold capacity and the swim to technique. Muscular endurance leads the fourth, and aerobic endurance leads the last block before 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.
- 01Environmental resilienceBike leg, 52% of the day90 × 52%47
- 02Aerobic enduranceBike leg, 52% of the day85 × 52%44
- 03Muscular enduranceBike leg, 52% of the day81 × 52%42
The bike takes 52% 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 Boise 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
- SupportSwim technical skill
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportBike aerobic durability
- SupportRun aerobic durability
- Weeks 6 to 9Foundation 2Closes with a recovery week
- PrioritySwim threshold capacity
- PriorityBike aerobic durability
- PriorityRun aerobic durability
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim muscular endurance
- SupportSwim technical skill
- SupportBike threshold capacity
- SupportRun threshold capacity
- Weeks 10 to 13Foundation 3Closes with a recovery week
- PrioritySwim technical skill
- PriorityBike threshold capacity
- PriorityRun threshold capacity
- SupportBike aerobic endurance
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim muscular endurance
- SupportSwim threshold capacity
- SupportBike aerobic durability
- SupportRun 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
- SupportSwim technical skill
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportBike aerobic durability
- SupportRun 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
- SupportSwim technical skill
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportBike aerobic durability
- SupportRun 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
6× climb-to-false-flat repeats
1.3 min at Zone 5, then 1.5 min at Zone 4, then 1.3 min at Zone 5, then 1.5 min at Zone 4, then 1.3 min at Zone 5, then 1.5 min at Zone 4, then 1.3 min at Zone 5, then 1.5 min at Zone 4, then 1.3 min at Zone 5, then 1.5 min at Zone 4, then 1.3 min at Zone 5, then 1.5 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
- 44 min
- Trains muscular endurance
- Supports strength force
- Supports high intensity capacity
- Supports threshold 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
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- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
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- 18
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- 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 | 0:46:24 | 3:18:55 | 2:23:16 | 6:38:35 |
| Trained1:51 /100m critical swim speed · 3.03 W/kg at 75 kg · 5:06 /km threshold pace | 0:39:19 | 3:03:15 | 1:59:08 | 5:51:42 |
| Competitive1:36 /100m critical swim speed · 4.15 W/kg at 75 kg · 4:20 /km threshold pace | 0:34:00 | 2:42:06 | 1:41:14 | 5:07:20 |
| Elite1:26 /100m critical swim speed · 5.27 W/kg at 75 kg · 3:50 /km threshold pace | 0:30:28 | 2:28:03 | 1:29:33 | 4:38:04 |
Pacing plan
- 0 km0.2%29.8 km/h2:27
- 1.22 km-5%54.1 km/h1:32
- 2.61 km0.4%28.8 km/h8:54
- 6.89 km4.3%14.4 km/h2:54
- 7.59 km0.7%27.4 km/h1:30
- 8.27 km3.5%16.5 km/h1:08
- 8.58 km-0.3%32.3 km/h23:39
- 21.3 km5.1%12.7 km/h6:22
20 more segments in the full plan.
- Run: reach 4:20 /km and this course gives back 44:22.
Where it is decided
In the first 26 km of the bike, and then on the Greenbelt.
The ride opens downhill and fast, and within 7 km it asks its first question. Four climbs in the next 19 km, among them the longest and the steepest of the day, all while the legs are fresh and the field is thick. Build a session from this file and the engine gives back six efforts of a minute and a quarter in Zone 5, each running straight on into a minute and a half in Zone 4 with only half a minute of easy pedalling before the next. That is the honest shape of these climbs. Several of these climbs do not hand you a summit to rest on. The road keeps rising gently after the steep part is over.
Answer each of those with a surge and the cost does not show on the bike. The next 28 km are flat and the average power recovers. It shows on the run, which the Trained band starts close to four hours in, in air that reached 42 C in 2024. The Greenbelt has shade, and the organiser says so. It does not have hills to hide a slowing pace behind. Every minute given away on the climbs comes back on those two flat loops, at a rate that feels unfair.
Getting it wrong
Training for the label. The organiser calls the bike hilly, so riders build their spring around long climbs, and Boise asks for about 17 minutes of climbing from a Trained athlete in a ride of three hours. Strength and force on the bike scores 46, a long way behind aerobic endurance at 85. The hours belong on steady road.
Racing the downhill start. The first 1.4 km fall at 5 percent out of the reservoir area and the whole field is excited. Then the first climb arrives at 7 km. Riders who carried their descent speed into it with a hard push hit 4.3 percent already above the number they planned, with the longest climb of the day still to come.
Pacing the second loop like the first. The run is two loops on the Greenbelt, the shade and the spectators are there both times, and the first loop feels generous. The heat is not generous. A Trained athlete who starts the run near four hours into a 39 C day needs a first loop that leaves room for the second.
Conditions on the day
- 2026high 39 C, low 21 C
- 2025high 34 C, low 17 Cwater 19 C
- 2024high 42 C, low 25 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 Boise 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
- 5:51:42
- Of the day on the bike
- 52%
- Dimensions scored per leg
- 12
- Season runway shown
- 24 wk
Questions people ask
- Is the IRONMAN 70.3 Boise bike course hilly?
- The organiser labels it hilly and describes a rolling tour of rural roads. The file climbs 519 m and descends 633 m, because it starts at Lucky Peak Reservoir and ends in downtown Boise. The steepest sustained climb is 355 m at 6.5 percent and the longest is 1.35 km at 5.1 percent. Across the whole race, 92.1 percent of the course is flat by distance.
- How hot is IRONMAN 70.3 Boise?
- The organiser logged highs of 42 C in 2024, 34 C in 2025 and 39 C in 2026. Heat is the largest single demand on this course. The water in Lucky Peak Reservoir was 19 C in 2025.
- Is the IRONMAN 70.3 Boise run flat?
- Yes. It is two loops on the Boise River Greenbelt Trail, which the organiser describes as flat and packed with shade and spectators. The file climbs 41 m over 21 km, and the engine reads the whole run 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 24 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.