70.3 vs full Ironman: what actually changes.

You already finish a 70.3. You want to move up to a full Ironman. The training does not double: it changes shape. Longest ride, longest run, weekly hours, nutrition, taper, race-day pacing — the seven things that actually shift, and how to plan them so the jump does not break you.

The move from 70.3 to full Ironman is not "the same, but twice." It's a different physiological problem. On a 70.3, most amateurs run out of engine before they run out of muscle. On a full Ironman, muscle failure and fuelling failure arrive before VO2max does. The training re-optimises around that.

Weekly hours: 8-14 becomes 10-18

A serious 70.3 build sits between 8 and 14 hours per week in the peak block. For a full Ironman, the same athlete needs 10 to 18 hours per week in the peak block. The delta is not "double" — it's about +2 to +4 hours. What matters is that the extra hours land almost entirely on the long ride and the long run.

If your 70.3 build had you at 12 h/week, your Ironman build lands at ~15 h/week in peak weeks. The extra 3 hours = a longer Saturday ride + a longer Sunday run. Swim and intensity sessions stay similar.

The long ride: 3h becomes 5h

The most obvious shift. A 70.3 build tops out at a 3 h to 3 h 30 long ride in peak weeks. A full Ironman build tops out at a 5 h to 5 h 30 long ride in peak weeks. The intensity target drops: 70.3 long rides sit at IF 0.75-0.80, Ironman long rides at IF 0.68-0.72.

You do not just add 2 hours at the same effort — you add 2 hours at a lower effort. If you hold 70.3 intensity for 5 hours, you cook your legs and the following long run collapses. The full Ironman long ride is deliberately easier per kilometre.

The long run: 1h30 becomes 3h

Same logic on the run. A 70.3 long run tops at 90 to 100 minutes. Full Ironman long runs go to 2 h 30 to 3 h. The extra hour+ is done in Z2 low, at 20-30 seconds per kilometre slower than 70.3 marathon pace.

The role of the run is different too. On 70.3 you're building running economy near threshold. On full Ironman you're building the neuromuscular tolerance to run for 3+ hours off the bike. Different systems. That's why the "long-run-off-a-2h-ride brick" is a peak-week staple for Ironman and rare for 70.3.

Nutrition: gels-and-drink becomes real food

Race-day fuelling for a 70.3 is 60-90 g/h of carbohydrate, mostly liquid + gels. Race-day fuelling for a full Ironman is 80-100 g/h for 8 to 10 hours. You can't do that on gels alone. Trained gut, mixed liquid + solid, some savoury food (rice cake, banana, salt) becomes non-negotiable.

Training implication: the long ride is where you rehearse Ironman race nutrition. Every long ride of the SPECIFIC block is a fuelling rehearsal at race-day intake. If your gut can't handle 90 g/h at 4 h into the ride, you fix it in training, not on race day.

Taper: 2 weeks becomes 3 weeks

A 70.3 taper is 10 to 14 days. Volume drops 30% in week -2, 50% in week -1. Intensity is maintained until race week. TSB target on race day: +5 to +15.

A full Ironman taper is 3 weeks. Volume drops 25% in week -3, 40% in week -2, 60% in week -1. Intensity is maintained until race week (same as 70.3). TSB target on race day: +10 to +20. The extra week matters: on a 5 h ride + 3 h 30 run day, latent muscle damage takes longer to clear than on a 3 h + 1 h 30 day.

Race-day pacing: IF 0.85 becomes IF 0.72

The single biggest shift in race execution. On a 70.3, top amateurs ride at IF 0.83-0.88 (bike leg 2 h 30, run leg 1 h 30). On a full Ironman, the same power profile would end the run at 25 km. Top amateur Ironman riders hold IF 0.68-0.72 for 5+ hours, so they can run a marathon after.

The single biggest execution mistake in a first Ironman: riding at 70.3 pacing. It always ends the same way — a strong first 20 km of the run, then a walk from km 25 to km 42.

Strength training: optional becomes structural

For a 70.3 you can get away without strength training. It helps, but the finish is possible without. For a full Ironman, 2 x 30-40 min strength sessions per week in the base and build blocks are structural: they protect the tendons and connective tissue that will be asked to hold up 3 h+ of running off the bike. Skip strength on Ironman training and injury rate rises 15-25% at the same weekly hours (Friel, 2024).