Ironman 70.3 Race Strategy: Pace to Run Well
Most bad 70.3 runs are paid for on the bike, usually in small, stupid ways that felt “fine” at the time. A few extra watts into every rise, a bit of showboating into a headwind, a cadence that turns your quads into damp cardboard. The point is not to arrive at T2 fast, it is to arrive at T2 runnable.
If you want to run well off the bike in a 70.3, ride with low variability and controlled intensity, fuel early, then treat the first 3 km of the run as a settling phase. Keep the bike smooth, cap the spikes, let your breathing come down, and only then start asking for goal pace.
Run durability is the whole game at this distance. Not in the Instagram sense of “mental toughness”, in the boring sense of keeping your breathing, gut, and mechanics usable after three-plus hours of work. The bike can feel like the main event because it’s long and measurable, but the run is where your race time gets decided, and the run is where your bike choices show up.
A lot of athletes can run a decent open half marathon. Fewer can do it after 1.9 km of swimming and 90 km of cycling. That gap is not mysterious. Running after cycling often costs more oxygen at the same pace, and it hits less experienced athletes harder. The early kilometres feel awkward because your breathing system is loaded, your posture changes, your legs switch from concentric cycling work to eccentric impact work, and everything is briefly inefficient. If you decide to “race” during that vulnerable window, you spike heart rate and effort, and this tends to stick.
The mistake is thinking the damage happens in one big moment. It is usually drip-fed. You do twenty little accelerations you never needed, you climb like it’s a short-course race, you coast every downhill and then punch out of every corner, you burn matches when you are already carrying fatigue. None of those moments feels catastrophic. Together, they build a run you cannot hold, even if your average bike effort looked sensible.
A steady bike is not a conservative bike. It is an efficient bike, and efficiency is what buys you a run.
The pacing principle that protects the run
Overbiking in a 70.3 is rarely “riding too hard” in the obvious way. It is riding at an intensity you can sustain for the ride itself, while quietly draining the parts of your system you need for the half marathon. You can ride a heroic bike split and still be walking at km 16.
Overbiking shows up as three things in real time.
First, you treat terrain as a speed problem instead of an effort problem. You try to hold pace up climbs and into wind by forcing big power spikes, then you tell yourself it’s fine because you recover on the downhill. The body does not see it that way. If you have to stand and stomp to keep the number on your screen pretty, that number is not helping you.
Second, you let adrenaline set the pace for the first third of the bike. It feels easy because you are excited, the field is moving, and you have fresh legs. That “this is too easy” feeling early is often a warning, not a green light. If you feel invincible in the first 30 km, act like a grown-up and back off slightly.
Third, you ride with high variability. It is the hidden killer of run legs. Your average power can look sensible, but your Normalised Power climbs because you surge. The Variability Index (VI) is the tell. A VI close to 1.00 is steady. A VI above about 1.05 tends to come with a bigger penalty later, even if your overall effort felt manageable.
If you want one simple weekend fix, stop chasing speed up every rise. Hold tension, not velocity. Let speed go where gravity and wind demand it, and keep the effort smooth. If you catch yourself repeatedly accelerating to “get back up to speed”, you are creating the very variability that makes half Ironman run pacing fall apart.
There is good data behind the idea that variability hurts the run, even when average intensity is matched. Stochastic efforts push you into anaerobic work more often, and that has consequences you do not fully undo with a few easy minutes later. The practical takeaway is blunt: if you want to run well, you ride like you mean it, not like you are constantly reacting.
Swim pacing that doesn’t poison the first hour
The swim is short in minutes and loud in consequences. A frantic first 200–400 m can spike lactate and heart rate, and that stress leaks into the first part of the bike. For age groupers, the time gained by sprinting early is often small, and the cost shows up later when the bike feels oddly hard and fuelling becomes messy.
Treat the swim as controlled work. Break it into thirds. Start “too easy” and focus on length and calm breathing. Find rhythm in the middle. Build slightly in the last third by holding form, not by thrashing. Draft when you can, because sitting in the wake saves energy you can spend where it actually changes the race.
If you come out of the water slightly calmer than the people around you, you are not losing the race, you are protecting it. If you come out breathing like you have been in an argument, accept that the next job is to settle, not to prove a point on the bike.
Bike execution: how to ride so you can run
The bike leg is the setup. You do not need to ride scared, you need to ride clean. Most athletes lose far more time on the run by making the bike messy than they ever gain by riding a few minutes faster, and “messy” often looks like lots of tiny decisions you could have skipped.
The settle phase (first 10–15 minutes)
You start the bike with an elevated heart rate from the swim, the change in posture, and the general race-day buzz. If you force power targets immediately, you create a double spike. This burns glycogen and makes breathing feel harder than it should, which then makes fuelling harder than it should.
Ride the first 10–15 minutes by feel. Keep it genuinely controlled, like RPE 5–6 out of 10. Let heart rate drop and stabilise. Use that time to start fuelling and get your head into the day. If you do this well, everything after it becomes simpler, because you are not fighting an artificially high baseline.
On-course moment 1 (early bike adrenaline)
You glance down and the watts look laughably easy, heart rate is climbing anyway, and you are overtaking people who swam faster than you. You decide you are not racing yet. You back off to a controlled feel for 10–15 minutes, take your first proper fuel, and keep your breathing quiet.
A useful rule here is behavioural, not physiological. If you feel compelled to “make time” in the first 10–15 minutes, you are not thinking about the whole race. Your job is to become steady.
Flats and headwind: hold tension, ignore speed
On flat sections, especially with a headwind, your job is steady pressure on the pedals. Headwind invites ego riding because speed drops and it feels like you are “doing nothing”. You respond by pushing too hard, then you wonder why the run feels like a treadmill set to spite.
Pick an effort and keep it. Let speed be whatever the conditions allow. If you ride with a power meter, you use it to keep the effort from drifting up. If you ride with heart rate, you use it to stop the slow creep into a higher zone when the wind annoys you. If you ride by feel, you use breathing and muscular tension as guardrails. If you are starting to pant on flat ground, you are already paying too much.
There is also a practical aero problem here. A long static position can leave you stiff, closed through the hips, and cranky in the lower back. Stand up briefly every 10–15 minutes, reset, then get back into position. The goal is not comfort, it is keeping your hips and breathing usable so the first run kilometres feel less like you are unfolding yourself.
Another quiet rule: if you find yourself staring at speed and getting annoyed, you are about to overpace. Shift attention to the one thing you can control, the effort you are producing.
Climbs: cap the cost
Climbs are where most overbiking happens, because you can justify almost anything as “course demands”. The bike does not demand heroics, it demands restraint.
Cap your effort on climbs. Never exceed 120% of FTP on hills. If it is steep, shift early and spin. Do not grind at a low cadence to prove a point. Low cadence increases torque, recruits more fast-twitch contribution, and leaves you with legs that struggle to handle eccentric loading on the run.
Sometimes sitting up is the smarter move. Hands on the bars can open your hip angle, make breathing easier, and reduce that diaphragm stress. You lose a little aero speed, but you avoid spiking effort and you keep the bike smoother overall, which matters far more than one dramatic climb split. A good general rule is to sit up once you drop below 18 km per hour (11 mi per hour), as aero gains become diminishable at that speed.
On-course moment 2 (long climb temptation)
You hit a long climb, the group around you stands and surges, and you can feel your ego reaching for the same match. You notice your breathing starting to sharpen and your quads taking over. You decide to cap it. You shift down, keep cadence up, let a few riders go, and crest without a burn in the legs. What it protects is your ability to hold stride length later, instead of collapsing into a seated shuffle at km 14.
If you want a simple self-check, it is this. If you are cresting climbs with burning legs, you are paying with the exact fibres you need for the run. You can get away with that occasionally in short-course racing. In a 70.3 it usually shows up right on schedule.
Downhills and tailwind: keep the legs alive
Coasting feels like “free recovery”. It is also how you inflate variability and make your legs stiff. Keep light pressure on the pedals. Maintain chain tension. It smooths your power, it keeps blood moving, and it helps clear the mess from any previous surge.
If the course is technical, braking and punching out of corners is another quiet variability trap. You can ride smoothly through bends, carry speed, and accelerate without a spike. That is a skill, not a fitness metric, and it fits the principle in Why you’re not getting faster: the forgotten role of technical skills in triathlon. Better handling buys a better run because it reduces needless surges and keeps you mentally calmer too.
A useful decision rule is to watch for frustration. Technical sections make people impatient. Impatience creates spikes. If you feel yourself trying to “make up time” after every corner, you are writing cheques you will cash later.
Overtakes, packs, and the urge to “prove it”
Even in non-drafting racing, other athletes affect your decisions. People pass you, you pass them, and you start making pacing choices based on the story in your head rather than the effort you planned. That story is rarely helpful.
Let faster bikers go early. Use them as pacing references, not targets. If you are a strong swimmer, the temptation is to “stay with” riders who are simply better cyclists. That usually ends with you paying on the run. If you are a strong cyclist, the temptation is to use the bike as your playground. You can still ride well while underbiking slightly relative to your capacity.
A calm race is not passive. It is controlled. The same approach shows up in Full distance race strategy: calm execution beats chaos. The distance changes, the decision-making does not. Smooth work beats dramatic work because it keeps the next discipline intact.
If you need one rule for overtakes, make it this. Do not respond to someone else’s pace change with your own pace change unless it fits your plan.
Cadence and torque: choose the fatigue you can afford
Cadence is a trade-off. Low cadence increases muscular load and torque. High cadence increases metabolic cost. Provided that you have worked on developing the required muscular durability, 75–85 rpm is a useful range for many athletes, You want to avoid high or low excesses. You don’t want to be spinning or grinding.
A simple cue is where you feel the work. If you feel it primarily in your quads on flat ground, bring cadence up slightly and smooth the pedal stroke. If you feel like you are stamping at the bottom of the stroke, you are building the wrong kind of fatigue. And if you don’t feel pressure throughout the pedal stroke, shift to a lower gear.
On-course moment 3 (wind section surging)
You turn into a headwind and your speed drops, the watts creep up as you try to “fix” it, and you notice your heart rate drifting. You decide to stop arguing with physics. You sit on your target effort, keep cadence in the protective range, take fluid, and let speed be slow. What it protects is your gut and your heat management, which are the first things to fall apart when you over-pace and then try to fuel through it.
Two pacing frameworks that actually work
A) Power and heart rate framework
Bike pacing targets depend on who you are and how long you will be out there. Intensity Factor (IF) and heart rate as a percentage of LTHR work well when you treat them as guardrails, not as targets you chase into bad decisions. RPE is the reality check when conditions change.
Cycling intensity targets (by target bike split)
| Target bike split | Primary target | HR (% LTHR) | RPE (1–10) | E-M-M-M guide | Description |
|---|---|---|---|---|---|
| Sub 2:30 (Elite/Top AG) | IF 0.82–0.85 | 80–85% | 6–7 | Medium | “Tempo” feel, tension present, no burning |
| 2:30–3:00 (Mid-pack) | IF 0.78–0.82 | 75–82% | 5–6 | Moderate | Steady aerobic, conversational but focused |
| 3:00+ (Completer) | IF 0.72–0.76 | 70–78% | 4–5 | Easy → Moderate | Comfortable endurance, feels sustainable |
Keep VI under 1.05 across all groups. That is the non-negotiable. If your VI is high, your run is the one that pays. If you notice your file looks like repeated spikes and drops, you fix the behaviour immediately by holding steadier effort over rises, pedalling the downhills, and accelerating out of corners without punching.
There’s also a blunt reminder about FTP reality. Many age groupers overestimate FTP because short tests reward anaerobic contribution. A “triathlon FTP” can be 5–10% lower than a “Zwift race FTP”. If you set targets off an inflated number, you will ride harder than you think you are riding, and you will call it “mystery fatigue” on the run. The decision rule is simple. If you keep “accidentally” riding above your target and telling yourself it still feels fine, your target is wrong, not your feelings.
Run pacing targets (by phase)
| Run phase | Primary target | HR (% LTHR) | RPE (1–10) | E-M-M-M guide | Notes |
|---|---|---|---|---|---|
| Settle (0–3 km) | Goal pace + 10–15 s/km | Below 85–88% | 4–5 | Easy | Keep it controlled until breathing and legs settle |
| Rhythm (3–14 km) | Goal pace (steady) | 85–88% | 6–7 | Moderate → Medium | Steady work, no “catch-up” surges |
| Endure (14–21.1 km) | Best sustainable effort | At or above 85–88% (drift allowed) | 8–10 | Medium → Mad | Only press if form and gut are holding |
The conversion rule that keeps you honest is also practical. A well-executed 70.3 run is commonly 5–10% slower than an open half marathon, or roughly open HM time plus 8–15 minutes depending on experience. Use that to choose a goal pace you can hold, rather than one you can flirt with for 5 km.
B) Effort-based framework using Easy / Moderate / Medium / Mad
If you want a 70.3 pacing plan you can execute when the course, weather, and your nervous system are doing their thing, effort works well. The mistake is treating effort as vague. It is only vague when you refuse to attach rules to it.
Easy is settle and control. Breathing is quiet, you could speak in full sentences, legs feel like they are working but not loading up. On the bike, Easy belongs in the first 10–15 minutes and in any section where you are trying to get back on top of fuelling, heat, or a rising heart rate. On the run, Easy belongs in the first 2–3 km, even if the pace looks too slow. If you cannot speak a full sentence in those early kilometres, you drop the effort immediately and let the system settle.
Moderate is steady aerobic work. You are focused, but not strained. Breathing is deeper, still controlled. On the bike, this is where most of your race sits if you are mid-pack. On the run, this is where you live from 3 km to roughly 14 km if the day is going well. If you feel you need to “push” to hold pace in the middle, you are already drifting into debt, and the correction is to ease slightly and return to smooth breathing.
Medium is race tension. You can hold it, but you notice it. Breathing is louder, and you would rather not talk. On the bike, Medium shows up on climbs and into wind, but it needs a cap so it does not become Mad. On the run, Medium is your “rhythm” pace when you are stable and fuelling is working. If Medium starts to feel like you are constantly gripping with your shoulders and jaw, you back off and find relaxation again.
Mad is for short moments only, and you should have a good reason. If you are hitting Mad repeatedly on the bike, you are building a run you cannot afford. Mad feels like panting, burning legs, and impatience. It also tends to come with silly decisions like hammering a hill at 120%+ FTP because someone passed you. If Mad shows up, the fix is behavioural: shift down, smooth the effort, take a breath, return to the plan you came with.
This is where Why triathletes overcomplicate their training matters on race day too. The simple version works. You can dress it up with metrics, but you still need the same discipline to keep the bike smooth and the run intact.
Run execution plan from T2
The first 10–15 minutes of the run are where most 70.3 pacing errors begin. Your breathing is adjusting, your posture is changing, your legs are dealing with impact again, and GPS is often useless near transition. If you run “goal pace” immediately, it can feel easy, then you discover at km 16 that you have been taking loans you cannot repay.
Run the first 2–3 km 10–15 seconds per km slower than goal pace. Think of it as buying stability. The ventilatory spike normalises, heart rate stops doing stupid things, and your legs get a chance to find rhythm before you ask for pace. The decision rule is clear. If you are trying to “catch up” early, you are borrowing from the part of the run that actually matters.
| Segment | What you do | Caps and cues | What it protects |
|---|---|---|---|
| T2 exit | Say “Slow” to yourself once, out loud if you need to | First minute is about control, not speed | Stops the ego spike that wrecks km 16–21 |
| 0–1 km | Do not look at current pace, focus on cadence and light feet | Short, quick steps, quiet contact | Lets breathing and mechanics settle |
| 1–2 km | Breathing check | If you cannot speak in full sentences, slow down immediately | Prevents early HR debt that sticks |
| 2 km marker | First watch check | If you are 10–15 s/km slower than goal pace, you are doing it right | Keeps you out of anaerobic borrowing |
| 2–3 km | Gradual descent toward goal pace | No surges to “catch up” | Avoids the pace yo-yo that wrecks rhythm |
| 3–5 km | Lock into steady rhythm | Smooth breathing, relaxed shoulders, tall posture | Builds a run you can hold past halfway |
On-course moment 4 (first 10 minutes, heavy legs)
You leave T2 and your legs feel heavy, the watch pace looks fast, and your breathing is higher than it should be. You decide to treat the first 2 km as a settling phase, not a test. You shorten the stride, keep steps quick, do a speaking check, and let pace fall where it needs to fall. What it protects is the middle 10 km, where early panic usually turns into slow bleeding.
The middle (5 to 14 km): hold pace without drifting into debt
Once you are stable, the run becomes an exercise in not letting small problems become big ones. Pace drifts up when you feel good. It drifts down when you stop paying attention. Heart rate drifts when heat and fuelling start to bite. None of those trends is fatal early, as long as you respond early, because early corrections are small corrections.
Hold goal pace by keeping effort steady. If you are on a hot day, respect heart rate caps over pace. Heat pushes heart rate higher for the same output, and it raises the risk of gut issues because blood flow is split between muscles and skin. If you try to force pace in that situation, you often lose the run completely, because you create a situation where you cannot cool and you cannot digest.
A simple rule for the middle is to keep your run boring. Smooth breathing, tall posture, and the kind of cadence that feels sustainable rather than urgent. If you start scanning for “places to push”, you are usually about to push in the wrong place, and the right move is to keep rhythm and save the press for later.
Your run pace is a summary of the swim and bike you have already done, the fuelling you have managed, and how well you have kept your head from getting involved. If you want a run that holds together, treat the run as the discipline you have been preparing for since the first stroke.
The final 7 km: when to press, and what must be true first
If you paced correctly, the race begins around km 14. Glycogen is lower, fatigue is higher, and your brain starts limiting output. You can still race here, but only if you have earned it. Earning it looks like being steady early, fuelling without drama, and arriving at km 14 with enough form left to increase effort without falling apart.
Pressing means you can hold form. If your posture is collapsing and you are clamping your shoulders up around your ears, “pushing” usually becomes “flailing”. The practical lever is cadence. When stride length shortens with fatigue, foot speed becomes the thing that keeps pace from falling off, without forcing you to overstride and break mechanics.
If the day is going well, you let effort rise in the final 7 km. Heart rate drift is allowed here. If the day is not going well, you aim for damage limitation by keeping cadence up, taking what fuel you can tolerate, and running the flats and downhills smoothly. You can press when you are still running with shape. If you are already losing shape, you protect what you have left.
On-course moment 5 (HR drift plus GI wobble)
At km 10–12 your heart rate is climbing for the same pace, and your stomach starts to feel sloshy. You decide to stop forcing it, because forcing it makes both problems worse. You back off slightly, switch to water and easier calories, and use the next aid station to reset your breathing and posture. What it protects is the ability to keep running instead of walking every station from km 14 onwards.
Fuelling and pacing as one system
If you overheat or over-pace, you must slow down to digest. You cannot force calories into a compromised gut. This is why smart pacing and smart fuelling are the same decision wearing different clothes.
On the bike, aim for 60–90 g of carbohydrate per hour. The bike is where the gut is most stable because heart rate is lower than the run and there is no impact. Treat the bike as the place to front-load fuel. Liquid calories often go down easier, and mixed carbohydrate sources (glucose plus fructose in a 2:1 or 1:0.8 ratio) can improve absorption because they use different transport pathways.
On the run, aim for 40–60 g of carbohydrate per hour, mostly gels or liquids. Impact makes GI distress more likely, and it punishes big lumps of food. This is why underfuelled bike legs lead to desperate run fuelling, and desperate run fuelling often leads to a sloshing stomach and a shuffle. The decision rule is to avoid “catching up” on the run. If you miss bike intake, you accept it and manage, you do not try to fix it with a stomach full of gel.
Hot conditions make the whole system more fragile. Expect heart rate to sit 5–10 bpm higher for the same output. Respect that. If you race your watch pace in the heat, you tend to lose both fuelling and pacing, because the body cannot cool, cannot digest, and then cannot run.
If you want nutrition to be useful rather than noisy, keep it simple. Simplifying triathlon nutrition: the myths and realities covers the same point in a broader way. You do not need novelty. You need repeatable intake your gut will accept.
Warning signs and corrections
Most races are salvageable early. They become unsalvageable when you ignore the signals and keep executing the original plan as if the body didn’t get the memo. The earlier you respond, the smaller the correction needs to be, which is why the skill is noticing, not suffering.
Yellow flags (adjust immediately)
Bike: panting on climbs. Shift down, lower power, keep cadence up. If you cannot control breathing, you are riding above what you can afford.
Bike: euphoria in the first 30 km. Adrenaline can make power feel “free”. Back off slightly and let the race settle.
Bike: VI creeping above 1.05. Stop chasing speed over rises and out of corners. Ride smoother.
Run: first 5 km splits faster than goal pace by 10 s/km. Force a slowdown immediately. This is the classic ego trap.
Run: bloating or sloshing. Stop solids and gels, switch to water and simple fluids, slow until it settles.
Each of these is a decision point. If you ignore them, you do not get to be surprised later. If you act on them, you often buy yourself a normal second half.
Red flags (survival mode)
Bike: cramping in quads or calves before T2. Hydration and salt become urgent, soft pedal, prepare for a conservative run plan.
Run: chills or goosebumps in the heat, or you stop sweating. Heat exhaustion risk, walk aid stations, cool aggressively, speed is no longer the priority.
Run: ammonia smell. Severe glycogen depletion, ingest sugar immediately (Coke is the classic fix on course).
Run: dizziness or tunnel vision. Hypoglycaemia or hypotension, walk, seek medical help if it persists.
The same principle applies. Small fixes early are boring. Big fixes late are humiliating, and slower.
Training implications (short, practical)
Pacing is a skill. You don’t read your way into it. You earn it by practising the same decisions you want to make on race day, especially when you are a bit tired and slightly bored, because that is most of real training.
First, build bike strength endurance. Low cadence intervals at 50–60 rpm at tempo or sweet spot power can build fatigue resistance in the fibres that otherwise blow up late.
Second, one “big day out” simulation once per block is enough. A 3–4 hour ride ending with 30–45 minutes at race intensity (IF around 0.80 is given), straight into a 20–30 minute run at target 70.3 pace. It validates fuelling, tests your pacing discipline, and gives you a clear reference for what “controlled” actually feels like when you are not fresh.
Third, frequent short bricks beat occasional long slogs. The key adaptation happens in the first 15–20 minutes of the run off the bike. Frequent short bricks, even easy ones, teach the switch and teach calm execution when your legs want to do something dramatic. They also fit the reality described in The time-crunched triathlete: maximising limited training hours, because you can build the skill without needing heroic weekends every week.
Fourth, teach the run to hold pace late. Long runs can include fast-finish segments, like the last 3–5 km at 70.3 pace. The point is the right stress at the right time, then enough recovery to absorb it.
The finish that actually runs well
A good 70.3 is controlled early. You earn the right to race by being boring when everyone else is excited. You keep the bike smooth, you keep fuelling simple, and you let the first 3 km of the run settle before you ask for pace. Then you get to do the rare thing in a 70.3, you run through people late instead of making apologies to them.
If you want me to apply this to your training and race calendar, and stop you doing the usual self-inflicted pacing errors, start here: Sense Endurance Coaching.
If you’d rather follow a plan that builds the bike durability and the run-off-the-bike skills without wasting your week, use one of my options here: Sense Endurance Coaching training plans.
Build strength where it matters, keep the work purposeful, and race with the calm you trained for.
Q&A
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Ride for low variability and controlled intensity. Keep VI under 1.05, cap climbs at 120% FTP, and avoid repeated surges that feel small but drain the run.
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Power spikes on climbs and into wind, chasing speed instead of effort, and riding the first 30 km on adrenaline while fuelling falls behind.
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A well-executed 70.3 run is commonly 5–10% slower than an open half marathon, or roughly open HM time plus 8–15 minutes depending on experience.
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Yes, but it starts with restraint. Run the first 2–3 km at goal pace +10–15 s/km, settle breathing and cadence, then aim to hold steady through 14 km before pressing late.
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Ignore the urge to “get moving”. Keep steps short and quick, do a breathing check, and only start chasing goal pace after the first 2–3 km.
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Many time-crunched age groupers do well around 75–85 rpm.
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Front-load on the bike at 60–90 g of carbohydrate per hour, then aim for 40–60 g per hour on the run. If GI distress starts, slow down and simplify intake.
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Treating the bike like a time trial and the run like an afterthought. Small surges and early ego pacing cost far more than they earn.
