Ironman 70.3 Race Strategy: Pace to Run Well
Most bad 70.3 run splits are paid for on the bike, usually in small ways that felt manageable at the time. A few extra watts into every climb, a response to a headwind that became a pacing argument, a cadence that turned the quads into something unreliable by kilometre sixty. The point of the bike leg is to arrive at T2 in a condition to run, not to arrive with the fastest split the legs could physically produce.
If there is a single principle worth internalising before the rest of this article, it is that run durability is the whole game at this distance. The bike feels like the main event because it is long and measurable and data-rich. The run is where race time gets decided, and the run is where every bike choice shows up on schedule.
01 | The Overbiking Problem
Overbiking in a 70.3 is rarely an obvious error. It is a series of small ones. It shows up as treating terrain as a speed problem rather than an effort problem — forcing power on climbs and into headwind to keep the number on screen looking right, recovering on the descent, and telling yourself it balances out. The body does not experience it that way. The effort spikes accumulate neurologically and metabolically in ways that average power does not capture.
It shows up as letting adrenaline set the opening pace. The first thirty kilometres of a 70.3 feel easy because the legs are fresh and the race environment is activating. That feeling is not permission. An athlete who feels invincible in the first quarter of the bike is almost always describing the effect of adrenaline rather than reporting accurate physiological information.
Most consistently, it shows up in Variability Index. The VI is the ratio between Normalised Power and Average Power and is the clearest single indicator of how steady or surgy a ride was. A VI close to 1.00 is a steady ride. A VI above 1.05 reliably produces a harder run, even when average intensity was matched, because stochastic efforts push repeatedly into anaerobic contribution that a few easy minutes never fully undoes. Watching for the VI creeping upward in real time — and correcting by stopping the chasing of speed over rises and the punching out of corners — is a more useful in-race intervention than any post-hoc analysis.
The practical rule: hold effort over terrain, not velocity. Let speed be whatever gravity and wind produce at the target effort. Repeatedly accelerating to recover a speed that the gradient or weather took away creates the precise variability that decides 70.3 run pacing.
02 | The Swim
The swim is short in elapsed time and significant in downstream consequences. A frantic opening 200 to 400 metres spikes lactate and elevates heart rate in a way that leaks directly into the first portion of the bike, making the early bike feel harder than the output justifies and complicating the opening fuelling window.
The swim divides cleanly into thirds. Start controlled — not slowly, but with genuine composure — focusing on stroke length and calm breathing rather than position in the pack. Find rhythm in the middle third. Build slightly in the final third by holding form rather than increasing rate. Drafting off faster feet when available reduces the energetic cost of the swim meaningfully and is worth the positional effort to find.
An athlete who exits the water breathing more calmly than those around them is protecting the bike, not losing the race. The opening kilometres of the bike require settling regardless of the swim, but that settling process is considerably easier and faster from a composed swim exit than from one where the cardiovascular system is still processing the swim's demands.
03 | Bike Execution
The settle phase matters more than most athletes allow for it. Exiting the swim with an elevated heart rate from the effort, the postural change of moving from horizontal swimming to upright cycling, and the general activation of race morning means that forcing power targets immediately creates a double spike. Glycogen burns faster and breathing is harder than the output warrants, which makes the fuelling window more difficult to manage.
The first ten to fifteen minutes should be ridden by feel at a genuine RPE 5 to 6 out of 10. Let heart rate settle. Use this window to take the first fuel and establish the day's rhythm. Done well, everything that follows becomes simpler because the physiological baseline is stable rather than artificially elevated. If the temptation in these opening minutes is to push because passing other athletes feels like opportunity, the correct response is to recognise this as exactly the pattern that sets up a deteriorating run.
On flat sections and into headwind, the job is steady pressure on the pedals at the target effort, regardless of what speed the conditions allow. Headwind invites ego riding because velocity drops and maintaining effort feels insufficient. The correct response is to pick the effort level and hold it, letting speed be whatever the conditions produce. A power meter keeps effort from drifting upward when wind pressure builds. Heart rate stops the slow zone creep. Feel uses breathing and muscular tension as guardrails — if breathing becomes laboured on flat ground at moderate effort, the pace is already too high. Standing up briefly every ten to fifteen minutes to reset hip position and lower back is worthwhile; a long static cycling position can leave the hips restricted and contribute to a compromised running posture off the bike.
Climbs are where most overbiking happens because the terrain provides cover for decisions that feel justified. A hard climb that produces burning quads costs exactly the fibres that hold stride length in the final kilometres of the run. The cap on climb effort is around 120 percent of FTP — steep enough to require shifting earlier and spinning rather than grinding low cadence. Low cadence on climbs increases torque demands and recruits fast-twitch contribution that accumulates across multiple climbs in ways that show up reliably at kilometre sixteen of the run. Sitting up on genuinely steep gradients opens the hip angle and eases diaphragm function; below around 18 kilometres per hour the aerodynamic cost of this is minimal, and the physiological benefit is real.
An illustration of how this plays out in practice: there is a long climb, the athletes around you stand and surge, and the competitive instinct reaches for the same response. Noticing the breathing beginning to sharpen and the quads beginning to dominate is the signal to cap it instead — shift down, keep cadence up, let a few riders go over the top ahead. The legs that arrive at T2 from that decision will run differently to the ones that crested with a burn.
Descents and tailwind sections create a different temptation: coasting as recovery. Coasting inflates variability and allows the legs to stiffen. Keeping light pressure on the pedals through descents maintains chain tension, keeps blood moving, and smooths the power file in a way that preserves the run. On technical sections with corners and braking, the habit of decelerating hard and then accelerating out is another quiet variability source. Carrying speed through corners and accelerating progressively rather than in a punch is a handling skill that has a direct impact on the physiological cost of the ride. The article on why you're not getting faster covers why technical skills in each discipline translate directly to race efficiency.
Other athletes affect pacing decisions in predictable ways. Faster riders passing early will generate the urge to respond. Athletes who swam faster and are now being overtaken will feel like targets. Neither of these is a useful racing signal. The plan exists for exactly this reason — to provide a pre-established response to conditions that invite deviation. Passing athletes on the run in the back half, having held the bike steady while they over-cooked theirs, is a more reliable experience than the alternative.
Cadence functions as a trade-off between muscular load and metabolic cost. Low cadence produces higher torque and recruits more fast-twitch contribution. High cadence raises oxygen cost. The useful range for most athletes is 75 to 85 RPM during the main portion of the ride, avoiding the extremes in either direction. The check is where the work is felt: if effort concentrates in the quads on flat ground, bringing cadence up slightly and smoothing the pedal stroke reduces the specific loading that most directly compromises the run.
04 | Pacing Frameworks
Two frameworks for executing the above exist, and the choice between them depends on what tools the athlete is comfortable using under race pressure.
The power and heart rate framework gives specific intensity targets calibrated to expected bike split. These are guardrails rather than numbers to chase — their value is in stopping the gradual drift upward that feels fine in the moment and manifests as a deteriorating run.
| Bike split | IF target | HR % LTHR | RPE | E-M-M-M | Description |
|---|---|---|---|---|---|
| Sub 2:30 | 0.82–0.85 | 80–85% | 6–7 | Medium | Tempo feel, tension present, no burning |
| 2:30–3:00 | 0.78–0.82 | 75–82% | 5–6 | Moderate | Steady aerobic, focused but not strained |
| 3:00+ | 0.72–0.76 | 70–78% | 4–5 | Easy to Moderate | Comfortable endurance, feels sustainable |
VI below 1.05 applies across all categories. If the file shows repeated spikes and drops, the correction is immediate — steadier effort over rises, pedalling through descents, progressive acceleration out of corners.
One practical caveat on FTP: many age-group athletes overestimate theirs because short efforts reward anaerobic contribution that is not available for ninety minutes of sustained cycling. A triathlon FTP can be five to ten percent lower than a figure established on a fresh standalone test or in an online racing environment. Racing off an inflated number produces efforts that feel controlled but are systematically above the sustainable ceiling, which the run reveals.
The effort-based framework using E-M-M-M applies the same logic without requiring devices to confirm what the body is already communicating.
Easy on the bike belongs in the opening ten to fifteen minutes and in any section where fuelling, heat, or a rising heart rate needs managing. On the run, Easy belongs in the first two to three kilometres regardless of how good the legs feel. If a full sentence is not available comfortably in these early run minutes, the effort drops immediately and holds there until it is.
Moderate is steady aerobic work — focused, not strained, breathing deeper but controlled. This is where most of the bike sits for mid-pack athletes and where the run lives from three kilometres to approximately fourteen when the day is going well. Needing to push to hold pace in the middle of the run is an early signal that the effort is already above what the remaining distance can support, and the correction is to ease back slightly rather than to grind through it.
Medium is race tension — holdable but noticeable, breathing audible, the preference would be silence. On the bike it appears on climbs and into wind but requires a ceiling so it does not become the sustained mode. On the run, Medium is the rhythm pace when the athlete is stable and fuelling is functioning. If Medium starts to feel like gripping through the shoulders and jaw, the correction is to back off and find relaxation before returning to pace.
Mad is for brief intentional moments only, and its appearance repeatedly on the bike is a reliable predictor of a run that will not hold its intended pace. If Mad is appearing because of a hill, a competitor, or a headwind, the response is to shift down, smooth the effort, breathe, and return to the plan.
05 | Run Execution
The first two to three kilometres of the run are where most 70.3 pacing errors begin. The ventilatory system is adjusting, the neuromuscular pattern is switching from cycling to running, GPS near transition is often unreliable, and the adrenaline of T2 makes the opening effort feel easier than it is. Running goal pace immediately in this window frequently produces a pace that borrows from kilometre sixteen to twenty-one.
The opening kilometres run ten to fifteen seconds per kilometre slower than goal pace. This is not conservatism — it is buying the stability that allows the subsequent kilometres to hold. In practical terms: in the first minute, focus is on short quick steps and quiet foot contact rather than speed. At the one-kilometre mark, a breathing check determines whether full sentences are available; if not, the effort drops until they are. At two kilometres, the watch gets its first look — ten to fifteen seconds slower than goal pace is the correct picture. The gradual descent to goal pace happens between two and three kilometres, with no surges to compensate for the controlled opening.
A scenario that illustrates this consistently: T2 exit, heavy legs, breathing higher than expected, pace on the watch looking fast relative to the effort required. The response is to treat the first two kilometres as a settling phase, shorten the stride, keep cadence quick, and accept a slow opening split. What that protects is everything from kilometre five to kilometre twenty.
| Run phase | Target | HR % LTHR | RPE | E-M-M-M | Notes |
|---|---|---|---|---|---|
| Settle (0–3 km) | Goal pace +10–15 s/km | Below 85–88% | 4–5 | Easy | Breathing and mechanics first |
| Rhythm (3–14 km) | Goal pace | 85–88% | 6–7 | Moderate to Medium | Steady, no compensatory surges |
| Final 7 km | Best sustainable effort | Drift allowed | 8–10 | Medium to Mad | Press only if form and gut are intact |
A well-executed 70.3 run is typically five to ten percent slower than an open half marathon, or roughly open half marathon time plus eight to fifteen minutes depending on training background. This is the realistic planning target rather than the aspirational one.
The middle kilometres, from three to fourteen, are sustained through not allowing small problems to become large ones. Pace drifts upward when the athlete feels good and stops paying attention. Heart rate drifts when heat and fuelling begin to create strain. On hot days, heart rate sits five to ten beats higher for the same output and managing to a heart rate ceiling rather than a pace target is the more useful guide. Forcing pace in those conditions typically produces a gut problem alongside the cardiac one, because blood is split between working muscles and skin cooling, and digestion loses.
From kilometre fourteen, if the race has been executed correctly, pressure can increase. Glycogen is lower, fatigue is higher, and the brain begins limiting output. The lever is cadence — when stride length shortens under fatigue, maintaining foot turnover preserves pace without the overstriding that breaks mechanics and raises injury risk. An athlete at kilometre sixteen with intact form and the pacing resource to press will pass several people who had a better bike split.
06 | Fuelling as Pacing
Fuelling and pacing are the same decision approached from different directions. Overheating or over-pacing compromises gut function, and a compromised gut cannot process calories at the rate the remaining race demands. The two problems then compound each other.
On the bike, sixty to ninety grams of carbohydrate per hour is the target, with liquid calories generally more reliable than solids at race intensity. Mixed carbohydrate sources using a glucose-fructose ratio of roughly 2:1 improve absorption because the two sugars use different intestinal transporters — the principle explained in detail in the article on simplifying triathlon nutrition. The bike is the most favourable window for nutrition because heart rate is lower than the run and there is no impact disrupting gut function. Front-loading here reduces the pressure on run nutrition.
On the run, forty to sixty grams of carbohydrate per hour is the target, primarily gels and liquids. The mechanical impact of running makes GI distress more likely and makes large boluses of food problematic. Attempting to catch up on missed bike calories through aggressive run fuelling is one of the more reliable paths to a sloshing stomach and a run that deteriorates into a walk between aid stations. Accepting a missed intake window and managing the remaining race conservatively produces a better outcome than trying to close the nutritional deficit at a point where the gut cannot support it.
07 | Warning Signs and Corrections
Most races are recoverable early and unrecoverable late. The skill is recognising signals when they are still small enough to address with small corrections.
On the bike: breathing becoming laboured on a climb is the cue to shift down, lower power, and raise cadence. Euphoria in the first thirty kilometres is the signal to back off slightly and let the race settle — adrenaline is reporting a false physiological picture. VI creeping above 1.05 requires immediately stopping the chasing of speed over rises and out of corners.
On the run: opening splits faster than goal pace by ten seconds per kilometre require a forced slowdown in the next kilometre, regardless of how it feels. Bloating or a sloshing sensation is the signal to stop solids and gels, move to water and simpler fluids, and reduce pace until the gut settles.
More serious signals require a different category of response. Cramping in quads or calves before T2 means hydration and salt become urgent, the final bike kilometres go soft, and the run plan adjusts to something the current physiological state can actually support. Chills or goosebumps in the heat, or a cessation of sweating, is heat exhaustion risk — walk aid stations, cool aggressively, and accept that finishing replaces pace as the objective. An ammonia smell on the run indicates severe glycogen depletion; cola from an aid station is the fastest available correction. Dizziness or tunnel vision means walking and seeking medical assistance if it does not resolve quickly.
08 | Training the Skills
Pacing is trained rather than read. The specific decisions the race requires — holding off the bike opening, capping climbs, maintaining VI discipline — are available on race day because they were practised in training under comparable conditions.
Low-cadence bike intervals at 50 to 60 RPM at tempo or sweet spot power build fatigue resistance in the specific muscle fibres that otherwise fail late in the bike and early in the run. The full rationale and protocols are in the article on big-gear cycling.
One simulation session per preparation block validates the whole system. A three to four-hour ride finishing with thirty to forty-five minutes at around 0.80 IF, straight into a twenty to thirty-minute run at target 70.3 pace, tests fuelling, pacing discipline, and the neuromuscular transition in a single combined effort. The feedback from one genuinely race-representative simulation is more useful than months of isolated sessions.
Frequent short bricks develop the transition skill more efficiently than occasional long ones. The relevant neuromuscular adaptation concentrates in the first fifteen to twenty minutes of the run off the bike. Repeating that specific window regularly, even at easy effort, trains the switch and develops the composure that the opening kilometres require. The specific session formats for this are covered in the article on run off the bike.
Long runs with fast-finish segments — the final three to five kilometres at 70.3 run pace — develop the capacity to maintain target pace under fatigue rather than learning to run it only when fresh. This is the specific quality that separates a run that holds from kilometre fourteen to twenty-one from one that deteriorates.
The time-crunched athlete's version of all of this is covered in the article on the time-crunched triathlete. Short bricks that develop a specific quality fit a compressed week better than heroic long sessions that require disproportionate recovery.
A good 70.3 is controlled early. The bike stays smooth, fuelling starts within the first fifteen minutes of riding, and the opening three kilometres of the run settle before pace is pressed. Every athlete who has run well through the field in the final seven kilometres of a 70.3 did so because those decisions were made in the first three hours, not the last thirty minutes. If you want to work with a coach who builds that execution framework into the preparation and holds you to it on race day, Sense Endurance Coaching is where to start.
If you are preparing from a plan, the sessions are structured to develop the specific bike durability and run-off-the-bike skills that race execution depends on. You can find the full range on the training plans page. The run well in a 70.3 is earned in the training block. Race day is the test.
