IRONMAN 70.3 · Redding · 23 May 2027
How to train for IRONMAN 70.3 Northern California
Read the organiser's pitch and Redding sounds like a gift. A net downhill bike. A flat run along the Sacramento River Trail with shade on it. A fast course for breaking a personal best. Athletes take the downhill part literally and plan a day that runs itself.
The numbers do not support that plan. Heat, not gradient, is the biggest demand on this course, on every leg. The organiser logged highs of 32 C in 2026 and 31 C in 2025, and a Trained athlete begins the run close to four hours after the swim start.
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.
- Swim1.93 kmDistance only
- Bike90.7 km669 m upCourse file
- Run21.5 km107 m upCourse file
The swim is 1 lap of Whiskeytown Lake at sunrise, 1.9 km of what the organiser calls tranquil water ringed by forested hills. Transition 1 sits in the parking lot at the lake.
From there the bike runs 90.7 km through Shasta County on smooth roads the organiser describes as rolling, and it ends in Redding far below where it began. They put the net loss at nearly 1000 feet. The file shows how it is spent. The first 8 km stay near the lake's height. Then the road falls away in steps, including 1.6 km at minus 6.3 percent, before a 651 m rise at 6 percent past kilometre 18. The middle rolls. Fourteen rises reach 3 percent or steeper across the whole ride, the steepest 338 m at 7.7 percent just after kilometre 53, and the last 16 km are close to level. Total climbing is 669 m against 901 m of descent.
The run follows the Sacramento River Trail, crosses the Sundial Bridge and loops through the riverfront parks to a finish near downtown Redding. 107 m of climbing over 21.5 km. Two long flat stretches carry 47 and 41 percent of the run leg between them.
Course shape by distance
- Flat 85%
- Climbing 6%
- Descending 9%
The longest stretches
- Bike, climbing0.34 km1% of the bike
- Run, flat10.1 km47% of the run
- Run, flat8.72 km41% 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.
Environmental resilience scores 90 on the swim, the bike and the run alike, and on the bike that single score outranks everything else in the cross-leg ranking. Aerobic endurance follows at 85 and muscular endurance at 82. Heat is not a footnote in Redding. It is the condition that defines the day.
The profile adds a second layer. High-intensity capacity reads 58 on the bike, well above the 40 on the swim and the run. Strength and force reads 48. Those are the fourteen rises doing their work. None is long, and each one asks for a short stretch above your steady power before the road hands it back. The run's surprise is technical skill at 56, above the bike's 41. A route that follows a river trail, crosses a bridge and loops through parks has more corners in it than open road.
A Trained athlete swims 38:50, rides 3:07:21 at 182 W and runs 2:01:58, for 5:58:09. Of that bike, roughly 27 minutes go to climbing and 10 to descending. The Competitive band finishes in 5:12:57 from 4.15 W/kg at 75 kg and 4:20 /km threshold pace. It gains 22 minutes on the bike and 18 on the run, and the run minutes are the harder ones to find, because they have to be found in the heat.
- Environmental resilience90
- Aerobic endurance85
- Muscular endurance80
- Threshold capacity70
- Aerobic durability65
- Threshold durability65
- Fueling resilience55
- Technical skill55
- 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 twelve dimensions from the course file and the same twelve from the athlete, whose side comes from thresholds and connected training history with a note on each score about its source and how much weight it bears. Where the athlete can already show what the course asks, there is nothing to train. Where the course asks for more, the difference is a gap, and gaps are ranked by how much of the race they fill.
A page with no reader behind it cannot know where anyone's gaps sit. So this season assumes they fall where Redding's demands are largest and lays out 24 weeks in 5 developmental blocks and a two-week taper. Aerobic endurance leads the first block in every sport. Durability leads the second, threshold durability on the bike and aerobic durability in the water and on foot. Threshold capacity takes the third, muscular endurance the fourth, and aerobic endurance leads again before the taper. Your own season is drawn from your numbers, and in a race this hot it will argue with this one about more than just order.
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%45
- 03Muscular enduranceBike leg, 52% of the day82 × 52%43
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 Northern California 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 threshold durability
- SupportRun aerobic durability
- SupportSwim aerobic durability
- Weeks 6 to 9Foundation 2Closes with a recovery week
- PriorityBike threshold 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 threshold 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 threshold 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 threshold 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
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
12× rolling-course surges
1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, then 1.3 min at Zone 5, 8.8 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
- 136 min
- Trains threshold durability
- Supports muscular endurance
- Supports high intensity capacity
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 | 0:45:50 | 3:23:22 | 2:26:41 | 6:45:53 |
| Trained1:51 /100m critical swim speed · 3.03 W/kg at 75 kg · 5:06 /km threshold pace | 0:38:50 | 3:07:21 | 2:01:58 | 5:58:09 |
| Competitive1:36 /100m critical swim speed · 4.15 W/kg at 75 kg · 4:20 /km threshold pace | 0:33:35 | 2:45:44 | 1:43:38 | 5:12:57 |
| Elite1:26 /100m critical swim speed · 5.27 W/kg at 75 kg · 3:50 /km threshold pace | 0:30:05 | 2:31:22 | 1:31:41 | 4:43:08 |
Pacing plan
- 0 km1.5%23.7 km/h1:22
- 0.54 km3.2%17.4 km/h1:39
- 1.02 km-0.9%35.3 km/h6:28
- 4.82 km5.3%12.3 km/h2:19
- 5.29 km-0.5%33.3 km/h4:41
- 7.89 km5.4%12.2 km/h3:47
- 8.66 km-6.3%59.3 km/h1:39
- 10.3 km-2.1%41.1 km/h0:25
63 more segments in the full plan.
- Run: reach 4:20 /km and this course gives back 45:12.
Where it is decided
On the Sacramento River Trail, in the heat, by what the bike left you.
The engine splits the run into two long flat stretches and a pair of short dips. Those two stretches are nearly nine tenths of the leg. There is nothing on them to change your rhythm and nothing to hide behind except the partial shade the organiser mentions. A Trained runner spends 2:01:58 there as the day warms around them.
What decides that run happens earlier, on the fourteen rises. The engine turns this bike into a session of twelve efforts of a minute and a quarter in Zone 5, each followed by close to nine minutes of easy riding. Look at that spacing. The rises are short and far apart, and in between the course is falling, which makes every one of them feel affordable. The steepest, at 7.7 percent past kilometre 53, takes 1.4 percent of the bike leg. Ride all fourteen as efforts and the heat collects the bill on the river.
Getting it wrong
The first mistake is trusting the net loss. A course that ends nearly 1000 feet below where it starts still asks you to climb 669 m, and the 651 m at 6 percent comes straight after the long drop from the lake, on legs that have spent most of the previous ten kilometres going downhill. It arrives before the rider is ready for it.
The second is pacing the flat finish of the bike like a time trial. The last 16 km into Redding are close to level and fast, and after the rolling middle they feel like the place to make up time. Minutes won there are cheap. The heat on the run charges for them at a much higher rate.
The third is running the first stretch of the trail at your spring pace. The Sundial Bridge and the parks bring spectators, and the early kilometres of the river path feel easy. With highs of 31 C in 2024 and 31 C in 2025, and a Trained runner still out there two hours later, the pace that feels easy in the first kilometre is not the pace the last ten will allow.
Conditions on the day
- 2026high 32 C, low 17 C
- 2025high 31 C, low 14 C
- 2024high 31 C, low 15 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 Northern California 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
- 5:58:09
- 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 Northern California bike course downhill?
- Downhill overall, not all the way. The organiser describes a nearly 1000-foot net elevation loss from Whiskeytown Lake into Redding. The file still climbs 669 m on the way while it loses 901 m, and the steepest rise is 338 m at 7.7 percent past kilometre 53.
- How hot is IRONMAN 70.3 Northern California?
- Hot. The organiser logged highs of 32 C in 2026 and 31 C in both 2025 and 2024, with lows between 14 C and 17 C. Heat tolerance is the largest single demand on the course.
- What is the water temperature in Whiskeytown Lake?
- The organiser's page carries no water temperature for any of the three years it lists. The swim is a single lap of 1.2 miles in the lake at sunrise. Check the athlete guide in race week for the wetsuit decision.
- Is the run course flat?
- Yes. The run follows the Sacramento River Trail, crosses the Sundial Bridge and loops through the riverfront parks, climbing 107 m in total. The organiser describes the river banks as partially shaded.
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.