Half Ironman Training: Structured Preparation for Your 70.3

1.9 kilometres of swimming, 90 kilometres of cycling, 21.1 kilometres of running — the middle distance, officially called 70.3 or half Ironman, is the fastest-growing format in triathlon. For good reason: it is long enough to demand real endurance, nutritional discipline and pacing, yet compact enough to prepare for alongside a job and a family. This article covers the physiological demands of the 70.3, how many training hours are realistically required, which sessions make the difference — and where most age-groupers lose their races long before they reach the start line.

What the middle distance demands physiologically

A half Ironman takes most age-groupers between four and a half and seven hours. That is the critical duration zone of endurance physiology: short enough to race at genuine intensity, long enough that fueling and fatigue management decide the outcome. The load per discipline typically looks like this:

• Swim (30–45 minutes): Intensity just below the aerobic threshold. Start too fast here and you pay for it for six hours — the swim should feel like a warm-up, not a race.
• Bike (2:30–3:30 hours): The centrepiece of the race. You ride at 70–78 % of FTP (Functional Threshold Power) — noticeably brisk, but controlled. You can only hold this intensity if you have practised it for hours in training.
• Run (1:40–2:30 hours): A half marathon on pre-fatigued legs, where the first five kilometres dictate the pace. Realistic is a pace 15–30 seconds per kilometre slower than your fresh half-marathon pace.

Energetically that means 3,000 to 4,500 kilocalories burned — against body carbohydrate stores of barely 2,000. Without continuous fueling from the bike leg onward, your body hits the wall by run kilometre 12 at the latest. The middle distance is therefore less a fitness test than a management race: equal parts fitness, nutrition and pacing.

Prerequisites: when you are ready for the 70.3

You do not need elite times, but you do need a resilient base. An honest checklist before you register:

• At least one year of regular endurance training — ideally including triathlon experience at sprint or Olympic distance.
• Swimming: 1.9 kilometres non-stop in open water under 50 minutes, without panic in the pack. If you can swim in a pool but have never seen open water, read our article on open-water swimming first.
• Cycling: 90 kilometres non-stop is routine, including basic comfort over three hours in the saddle.
• Running: A half marathon under roughly 2:10 hours — not as a performance goal, but as proof of orthopaedic resilience.
• Weekly volume: You currently train 6–7 hours per week and can build that up over months without knees, Achilles tendons or everyday life rebelling.

If you miss two or more of these points, another year of base work is the faster route — you will then start with genuine prospects instead of a survival story.

Weekly volume: 8 to 12 hours, distributed correctly

The most common question before a half Ironman is about hours. The answer: for a safe, healthy finish, 8 to 10 hours per week is sufficient. Athletes targeting a time under 5:30 hours land at 12 to 14 in peak weeks. The distribution follows race logic:

• Cycling around 50 %: 4–6 hours. The bike is the longest discipline and the muscular preparation for the run — the biggest lever sits here.
• Running around 30 %: 2.5–4 hours. Running is orthopaedically the most expensive discipline; more volume rarely brings more, often just injuries.
• Swimming around 20 %: 2–3 sessions of 45–60 minutes. Two technique sessions beat one tortured endurance set — details in the article on triathlon swimming technique.

Two structural rules are non-negotiable. First: every fourth week is a deload week at 60–70 % of normal volume — adaptation happens there, not under load. Second: volume increases by no more than 10 % per week. Jumping from 7 to 12 hours does not mean training harder; it means training shorter — because you are injured by week three.

The three key sessions of the week

In a ten-hour week, three sessions decide your race result. Everything else is important but interchangeable base work:

• The long ride (3–4 hours): Weekly, with built-in blocks at planned race pace — for example 3 × 30 minutes at 70–75 % of FTP. Here you practise two race-day skills at once: sitting in the saddle for hours while eating and drinking.
• The brick session: Cycling followed immediately by a run. The most specific building block in all of triathlon training — details in the next section and in the article on brick training.
• The tempo session: Alternating weekly between bike and run — threshold intervals such as 2 × 20 minutes on the bike or 3 × 10 minutes running. It raises the threshold from which your race pace is derived as a percentage.

Add two easy swim sessions, one relaxed endurance run and ideally 15–20 minutes of strength training twice a week. The 80/20 distribution applies here too: 80 percent of your time stays at easy base pace, only 20 percent is intense. Anyone who trains "grey" in half Ironman preparation — every session moderately hard — becomes moderately slower on the middle distance.

Brick training: the most specific building block

The switch from bike to run feels like running on borrowed legs: blood flow sits in the cycling muscles, and your stride cadence has to detach from the pedal rhythm. Brick sessions train exactly this sensation — and it is trainable.

• Short bricks weekly: 60–90 minutes of easy cycling, then 15–20 minutes of running at race pace. Short, frequent, unremarkable — and enormously effective for transition economy.
• The big brick every two weeks: Half the race distance in one go, for example 60 kilometres of cycling with 2 × 20 minutes at race pace plus 10 kilometres of running at goal pace. This is your dress rehearsal: equipment, fueling, pacing — everything as on race day.
• Spin deliberately over the final kilometres: Ride the last five bike kilometres slightly easier with a higher cadence — this relaxes the leg muscles for the start of the run.

The goal: after three or four bricks, the "concrete legs" effect shrinks from 2 kilometres to 400 metres. It never disappears entirely — but it turns from a showstopper into a footnote.

Race pace and pacing: the race is lost on the bike

The most valuable statistic of the middle distance: most run collapses are not caused by poor run training, but by 10 to 15 watts too many on the bike. Pacing references for age-groupers:

• Swim: Comfortably brisk, 85–90 % of your training threshold pace. The two minutes a hard swim gains, it costs ten at the end.
• Bike: Intensity Factor 0.70–0.75 (i.e. 70–75 % of FTP), first-timers closer to 0.68. Without a power meter: a pace at which you could still speak short sentences but have no desire to.
• Run: Deliberately run the first 3 kilometres 10–15 seconds slower than goal pace — the adrenaline trap. From kilometre 10, freshness decides whether you can speed up. Negative splits on the 70.3 are not a dream but the standard outcome of good pacing.

Fueling: the fourth discipline you train

On the middle distance, nutrition is trainable — and mandatory. The targets: 60–90 grams of carbohydrates per hour from the bike leg onward, 500–750 millilitres of fluid per hour, 300–600 milligrams of sodium per hour. Intake happens almost entirely on the bike, because the stomach is most cooperative there: two to three gels per hour, isotonic drink, nothing new on race day. The mechanics behind it — absorption limits, glucose-fructose blends, gut trainability — are explained in the article on marathon fueling; the principles are identical, just longer. And the days before: clean carb loading over 36–48 hours fills your stores above normal levels — the most valuable free reserve in a four-to-six-hour race.

The 16-week structure at a glance

A realistic 70.3 build divides into four blocks — assuming an existing base from a triathlon beginner plan:

• Weeks 1–6, base: Build volume from 8 to 10 hours, almost all of it easy. Technique swimming, long rides without pace blocks, short bricks. Boring — and exactly right for that reason.
• Weeks 7–12, build: The specific phase: race-pace blocks inside the long ride, big bricks every two weeks, threshold intervals. Peak weeks at 12–14 hours. Ideal: a B-race (Olympic distance) in week 10 or 11 as a form test.
• Weeks 13–14, peak: The longest brick of the preparation (e.g. 70 km bike + 12 km run at race pace), then the reduction begins.
• Weeks 15–16, taper: Cut volume by 40–60 %, keep short intensity. The complete logic is in the article on tapering — the same rules apply to the 70.3 as to the marathon.

The most common mistakes in half Ironman training

• Riding the bike too hard — in training and in the race. The middle distance is lost on the bike, not won. If you cannot hold IF 0.75 discipline, the half marathon becomes a walk.
• Neglecting the swim. 20 percent of training volume feels unfair for 30 race-day minutes — but a poor swim costs energy and nerves that are missing on the run. Water twice a week is the minimum.
• Testing fueling for the first time on race day. No untrained gut tolerates 80 grams of carbohydrate per hour. Every long session from week 7 onward is a nutrition rehearsal.
• Skipping the deload week. Build for four weeks straight and you accumulate fatigue instead of fitness. The body adapts during rest, not under load.
• New equipment on race day. New wetsuit, new saddle position, new gels — the classic act of self-sabotage. Everything used on race day has at least three training outings behind it.

How Peakora plans your 70.3 preparation

The Peakora engine plans triathlon across all three sports: TSS from swimming, cycling and running feeds into one shared load model, the 80/20 distribution is monitored per sport, and brick sessions are a fixed part of the build phase — including a written rationale for why exactly this session is scheduled today. Your race date drives the periodisation: base, build, peak and a two-week taper are laid out backwards from your 70.3, and the fueling calculator delivers the hourly plan for carbohydrates, sodium and fluid.

Frequently asked questions about half Ironman training

How long does it take to finish a half Ironman?

Most age-groupers finish a 70.3 in 4:30 to 7 hours. Elite athletes stay under 4 hours. Race organizers typically set time limits of 8 to 8.5 hours, with intermediate cut-offs after the swim and on the bike course.

How many hours of training per week does a half Ironman require?

For a safe finish, 8 to 10 hours per week is enough; for ambitious time goals, 10 to 14 hours in peak weeks. Volume matters less than distribution: roughly 20 percent swimming, 50 percent cycling, 30 percent running — plus every fourth week easy.

Can a half Ironman be your first triathlon?

Yes — with 9 to 12 months of structured preparation, a 70.3 is realistic as a first triathlon, provided you are comfortable swimming in open water. A smarter path leads through a sprint or Olympic distance race first, to learn transitions, start-line stress and race pacing.

What should I eat and drink during a half Ironman?

From the bike leg onward: 60 to 90 grams of carbohydrates per hour, plus 500 to 750 millilitres of fluid and 300 to 600 milligrams of sodium per hour. The bike is your buffet — intake gets harder on the run. Rehearse the entire strategy in every long training session.