Free 12-week Ironman build-phase training plan

Make that all-important leap from base to build phase and get set for Ironman race-day success. Dermott Hayes has the training plan…

12-week Ironman build-phase training plan

There’s no avoiding the fact that big sessions for an Ironman are done in the final peak phase, but before you get there the real hard grind must be completed in the build phase. Having executed a solid Iron-base phase, you should have improved aerobic efficiency, be comfortable with the increasing training volume and have spent time looking at your technique. Now the real work starts.


The build phase is the bridging section of IM training and is crucial to race-day success. There needs to be a noticeable increase in distances, a greater focus on strength/power development and brick sessions need to be started to help find your race pace.

You can expect to develop long runs up to 28km, long rides up to 160km, plus a long 4km swim. However, the real benefits are found in the interval and tempo sessions, where the focus is on improving power and strength – through stressing the anaerobic system – so that you can better cope with the physical demands of racing over 226km. Once your anaerobic system begins to work more efficiently, it will drag your aerobic system up and so your ‘sweet spot’ for racing an Ironman will improve, allowing you to achieve greater pace.

Key to this phase is the promotion of power, so there’s a focus on this in all disciplines. In the swim we introduce pull buoy and paddles as tools to help develop greater upper body power. On the bike we include hill-specific workouts, spending time both in and out of the saddle, as well as ‘overgearing’ – a drill where you cycle at a resistance one or two gears bigger than usual. The run sessions also include hill sessions, and, where possible, I encourage you to include rolling hills in the longer endurance runs.

Having not dedicated much time to this intensity of training in the base phase, it probably will feel stressful, so accept that it will take a couple of weeks to adapt physiologically before you see any improvements.

Spend time looking at the course profile and terrain for your Ironman race, and where possible try to simulate the course into some of your longer sessions. Also note: this plan does not include prescribed open-water swimming, but if you are able to include open-water time, (which I advise) it could take the place of the long endurance sets.


Make inclines your friend. Strength work will pay dividends on race day.


Practise time in the aero position on the bike. Play around with set-ups to find the most comfortable.


Recovery between sessions is vital: prepare meals in advance, use foam rollers, sleep as much as you can.


Be very clear as to what pace/power/heart rate you’re aiming for in each stage.

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Top image by Steve Sayers