IRONMAN 70.3 · Frankfort · Last raced 20 Sept 2026
How to train for IRONMAN 70.3 Michigan
The organiser sells Frankfort, on the shores of Lake Michigan, as approachable, and on paper it is. A sheltered bay for the swim, a bike the athletes voted Best Bike in North America in 2025, a run the organiser calls pretty flat. Approachable gets read as forgiving. It is the opposite. A course with almost no terrain gives you nothing to hide behind and nothing to pace against except the number you chose before the start.
Nearly 96 percent of the course is flat by distance. What decides a day of 5:49:25 here is not a hill. It is whether you can hold one steady effort on an open highway for three hours and still run 21.2 km once the day has warmed up. The race was last held on 2026-09-20, and the organiser has not yet published the next date.
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.
- Swim1.94 km0 m upCourse file
- Bike90.4 km320 m upCourse file
- Run21.2 km70 m upCourse file
Betsie Bay holds the whole swim, 1 lap of 1.9 km entirely inside its protected water. Start and finish sit right next to transition. The organiser logged it at 20 C in 2025 and at 16 C in 2023, so the temperature moves from one year to the next.
The bike leaves Frankfort for highway M-22 and the roads of Benzie County, 90.4 km built from two out-and-back sections, largely on M-22. The file measures 320 m of climbing, and it sits in a handful of places. A pair of short rises just before 20 km. A hill around 53 km that you climb, cross at the top and then descend again. And the steepest ramp of the day, 550 m at 5.6 percent, about 3 km before the ride ends. Between them lie two long, level stretches of highway, 30.8 km and 22.8 km, with nothing on them.
The run is two out-and-back loops on paved trails and roads around Betsie Bay, between the City of Frankfort and the Village of Elberta. The engine reads all 21.2 km of it as one flat segment. From the far side of the bay near Elberta you can still see and hear the transition area and the finish line.
Course shape by distance
- Flat 96%
- Climbing 2%
- Descending 2%
The longest stretches
- Bike, flat30.8 km34% of the bike
- Bike, climbing0.55 km2% 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 first, muscular endurance a close second, and on the bike above all. The demand model scores those two at 85 and 81 on the bike, with threshold capacity at 70 behind them, and because the bike is 52 percent of a Trained athlete's day, the six largest demands on the whole course all belong to the bike. The run's top pair reads 85 and 81. The swim's reads 85 and 80.
Look at what is missing. High-intensity capacity scores 48 on the bike and strength and force 44, both well down the list, because five short climbs across 90 km do not add up to a hilly race. Feed this bike to the engine and ask for a course session and it hands back five one-minute efforts in Zone 5, each separated by more than half an hour of easy spinning. That is an honest picture of the leg. The hard part is short. The easy part is almost all of it.
The bands put figures on that. A Trained athlete swims 38:57, rides 3:00:09 at 182 W and runs 2:00:19. The Competitive band finishes in 5:05:17 from 4.15 W/kg at 75 kg and 4:20 /km threshold pace, about 21 minutes quicker on the bike and 18 quicker on the run. None of that difference is found on the climbs. It is found on the flat, in a higher number held without a break.
Environmental resilience scores 60 on every leg. The organiser logged highs of 27 C in 2024, 26 C in 2025 and 24 C in 2023. For a Trained athlete the run starts more than three and a half hours after the gun, and it is run in whatever the day has become by then.
- Aerobic endurance85
- Muscular endurance80
- Threshold capacity70
- Technical skill68
- Aerobic durability65
- Threshold durability65
- Environmental resilience60
- 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 reads the same twelve dimensions from two directions. The course side comes from the file above. The athlete side comes from thresholds and connected training history, and every score carries a note on what it was read from and how much weight it can bear. A gap exists only where the course asks for more than the athlete can show. The gaps are then weighted by the share of the day each one fills, which on this course means a bike gap counts for roughly four and a half times a swim gap of the same size.
There is nobody behind this page, so the season beneath it cannot see any gaps. It takes the plainest assumption, that they fall where the demand is largest, and spreads 24 weeks across 5 developmental blocks before a two-week taper. Aerobic endurance leads the first block in all three sports. The second block hands the swim to technical skill and the bike and run to aerobic durability. Threshold capacity takes the third, muscular endurance the fourth, and aerobic endurance returns to lead the last. A member's own season starts from their own numbers and will not look like 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, 52% of the day85 × 52%44
- 02Muscular enduranceBike leg, 52% of the day81 × 52%42
- 03Threshold capacityBike leg, 52% of the day70 × 52%36
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 Michigan 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
- SupportSwim technical skill
- SupportBike aerobic durability
- SupportRun aerobic durability
- Weeks 6 to 9Foundation 2Closes with a recovery week
- PrioritySwim technical skill
- PriorityBike aerobic durability
- PriorityRun 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
- SupportSwim technical skill
- 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
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportSwim technical skill
- 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
- SupportBike threshold capacity
- SupportRun threshold capacity
- SupportSwim threshold capacity
- SupportSwim technical skill
- 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
5× course-matched climbs
1 min at Zone 5, then 1 min at Zone 5, then 1 min at Zone 5, then 1 min at Zone 5, then 1 min at Zone 5, 33 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
- 162 min
- Trains anaerobic capacity
- Supports strength force
- Supports muscular endurance
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 | 0:45:58 | 3:15:33 | 2:24:42 | 6:36:13 |
| Trained1:51 /100m critical swim speed · 3.03 W/kg at 75 kg · 5:06 /km threshold pace | 0:38:57 | 3:00:09 | 2:00:19 | 5:49:25 |
| Competitive1:36 /100m critical swim speed · 4.15 W/kg at 75 kg · 4:20 /km threshold pace | 0:33:41 | 2:39:22 | 1:42:14 | 5:05:17 |
| Elite1:26 /100m critical swim speed · 5.27 W/kg at 75 kg · 3:50 /km threshold pace | 0:30:11 | 2:25:33 | 1:30:26 | 4:36:10 |
Pacing plan
- 0 km0.1%30.3 km/h37:24
- 18.9 km5.2%12.5 km/h1:06
- 19.1 km0%30.8 km/h0:28
- 19.4 km3.5%16.5 km/h1:47
- 19.9 km0.2%29.8 km/h1:19
- 20.5 km-4.5%52 km/h0:52
- 21.3 km0.1%30.3 km/h1:00:55
- 52 km5.3%12.3 km/h1:56
15 more segments in the full plan.
- Run: reach 4:20 /km and this course gives back 44:08.
Where it is decided
On the long, level highway between the first rises and the hill near 53 km.
That one stretch of 30.8 km holds 34 percent of the bike leg, the biggest single block of the ride, and the 22.8 km stretch after the hill holds roughly another quarter. Nothing on either one tells you how hard you are riding. No gradient worth the name, and a field of riders around you that sets its own pace. A rider who drifts ten or fifteen watts above 182 W here feels nothing wrong and finds out on the second loop of the run.
The climbs themselves are cheap. The 5.6 percent ramp near the end of the ride takes 1.8 percent of the bike leg. It feels important because it is steep and it is late, and it changes almost nothing.
Then the run, which is flat and quiet in its demands and punishes whatever the bike left behind. Two loops out to Elberta and back, within sight of the finish even at the far end. A runner who rode the highway evenly passes people on the second loop. One who rode it by feel gets passed.
Getting it wrong
Training for the hills is the first mistake. The organiser mentions a few, riders read that as a warning, and they spend spring on climbing repeats for a course whose steepest climb fills under two percent of the ride. The time that matters is spent seated and low on M-22, holding one number.
The second is the opening 19 km. They are flat, the legs are fresh, and nobody has a reason to hold back. Riders who set their power here by how they feel carry that number into the long stretch that follows, and it is the wrong number for three hours.
The third is the heat on the run. Starting the first loop at the pace you ran in spring, when the day reached 27 C in 2024, is how a flat half marathon turns into a long walk back from Elberta.
Conditions on the day
- 2025high 26 C, low 14 Cwater 20 C
- 2024high 27 C, low 16 Cwater 19 C
- 2023high 24 C, low 13 Cwater 16 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 Michigan 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
- 5:49:25
- Of the day on the bike
- 52%
- Dimensions scored per leg
- 12
- Season runway shown
- 24 wk
Questions people ask
- How hilly is the IRONMAN 70.3 Michigan bike course?
- Hardly at all. The organiser describes a few hills on a course that is mostly rolling or flat, and the file measures 320 m of climbing over 90.4 km. The steepest sustained rise is 550 m at 5.6 percent, about 3 km before the ride ends.
- What water temperature should I expect in Betsie Bay?
- The organiser records 20 C in 2025, 19 C in 2024 and 16 C in 2023. The swim is one loop entirely inside protected Betsie Bay, with the start and finish next to transition.
- What is the IRONMAN 70.3 Michigan run course like?
- Two out-and-back loops on paved trails and roads around Betsie Bay, between the City of Frankfort and the Village of Elberta. The organiser calls it pretty flat, and the file reads as one flat segment from start to finish.
- 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, and a member's season starts from their own numbers.
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.