Half Ironman (70.3) Training Plan: How to prepare for a middle distance triathlon

A middle-distance triathlon, also called a 70.3 or half Ironman, covers a 1.9km swim, a 90km bike and a 21.1km run.

It sits between the Olympic distance and the full Ironman, which is why it is widely known as the "half Ironman" or middle distance.

Most athletes can go from zero to the start line in around six months by training five-six days a week and following one rule above all others.

Each person has different motivations for completing a 70.3, is at a different point in their fitness journey, has different amounts of time to commit to training, has different other life stresses and a different amount of money to invest in the journey.

You need to be realistic about what you can commit to, what you want to achieve, and what you can manage without injury or illness.

One rule beats every session. Consistency.

No single workout matters as much as turning up regularly. Whether you run for 45 minutes or 60, or push hard for four minutes or five, every session beats doing nothing at all.

Most athletes who miss the start line do so because they procrastinated over the detail and forgot to train, not because they chose the wrong interval.

Consistency is the single biggest predictor of reaching a 70.3 start line healthy and prepared. Routine beats motivation, because motivation fades on the cold, wet, dark mornings, but a fixed routine does not.

The athletes who succeed treat training as a non-negotiable part of the week rather than something they fit in when they feel like it.

Two principles carry the whole plan:

• Something always beats nothing. A shortened session is still progress; a skipped one is not.
  
  
• Routine beats motivation. Lock training into your week and you no longer rely on feeling inspired.
  
  

Commitment

With a sensible level of dedication, the zero-to-70.3 timeline is around six months. During that block you should expect to train in some form on at least six days every week, with most days lasting 60 to 90 minutes and two longer sessions of two to four hours.

Be realistic about what you can commit to without injury or illness, and bring your family and friends along for the journey, because their support makes the early alarms far easier. Here is the commitment in plain terms:

• ~6 months, zero to start line
• 6 days a week
• 60 to 90 min most days, 2 to 4 hrs twice
• Early alarms beat motivation
  
  

A full week typically adds up to around 11 sessions: three swims, three bikes, three runs and two strength sessions across six or seven days.

That total is why structure, not heroics, gets you to the finish.

You will need to find out when you can swim at your local pools, as the 'serious' swimmer times are often early morning and late evening.

You will need to run when it’s dark, wet, cold and windy.

You will need to work out how you will do you bike training (outdoors, indoors on your bike with a turbo or at a gym on a Wattbike).

You will need your family and friends to understand and support the journey that you are going on.

Three swim sessions a week is the sweet spot for a middle-distance triathlon, and technique should always come before volume. Unlike cycling and running, swimming more with a poor stroke does not make you faster; it just embeds bad habits.

• 3 swims a week
• Technique over volume
• Build up to the full 1900m
• Open water in your wetsuit and tri-suit
  
  

If you swam as a child, this is the easy leg. If not, film your stroke (ideally underwater), compare it against good technique, or invest in coaching. Swim fast occasionally, swim slowly often, but focus on technique every time. As race day nears, cover the full 1.9km most sessions so you are confident cut-offs will never be an issue.

As open water warms up, add one open-water swim a week in a safe, supervised or organised environment. Practise in your wetsuit with your tri-suit underneath - meaning there are no surprises on race morning.

The bike accounts for roughly half of your total race time, so it deserves a lot of attention, and comfort matters more than fast wheels. If you invest money for the cycling portion of a 70.3, a professional bike fit delivers the biggest return, because staying comfortable for three to five hours in the aero position is the priority.

Build endurance with longer steady rides outdoors at least once a week, and twice as the race approaches. These should be continuous and conversational rather than full of lung-busting efforts: if you can talk in full sentences, the intensity is about right. Top that up with one or two short indoor interval sessions of up to an hour, on a turbo or Wattbike, to add some quality.

Riding outside in all weathers also builds the bike-handling skills you will need on an unfamiliar course.

Running in a triathlon is different from standalone running because you do it tired, after three to five hours of racing. Your 70.3 run will have little in common with a fresh half-marathon time, so train for fatigue rather than speed.

Around 90% of triathlon training injuries come from running, so progress carefully. Run easily and conversationally for 30 to 60 minutes, three or four times a week, and build one of those runs towards 21.1km as race day approaches. Increase weekly volume by no more than 10% and listen to your body.

Track sessions can sharpen top-end speed, but they are also the fastest route to injury, so use them sparingly, if at all.

Strength and conditioning is essential to staying consistent, even though it is most athletes' least favourite session. Two sessions a week, whether weights for lean muscle rather than mass, Pilates or yoga, noticeably improve resilience and help prevent the injuries that derail training blocks.

It is the work that keeps you on the start line, and it is the easiest discipline to drop when life gets busy. Protecting those two sessions protects the other nine.

S&C will help prevent injuries and make sure you get to the start line.

Within eight weeks of any middle-distance event, training should be tailored to the specifics of the race. The principles below apply to any 70.3 course, whether it is a UK race like ATW's Box End Triathlon, the Lakesman, IM Swansea or an event abroad.

The swim

Decide how you will start. Many races offer a mass start or a rolling start over a timing mat, and your choice depends on your confidence and whether you want a competitive time. Whichever you pick, practise sighting buoys, swimming in a crowd and on other swimmers' feet, and breathing to both sides. Where possible, swim the actual course beforehand to learn the sighting lines and water conditions.

The bike

Know the course profile and the effort level you will hold across it, whether you measure it by power, heart rate or perceived effort. Practise climbing and descending if the route is lumpy, and ride the course in advance if you can. Equally important is keeping your bike moving: service it, carry the spares you need, and be able to fix a puncture or free a jammed chain. A mechanical you cannot solve is an avoidable DNF.

The run

Practise running off the bike. Brick sessions, a short run straight after a ride, teach your legs to cope with the strange first one to two kilometres of the run leg. Build these towards 15km if you are in good shape, and rehearse the tight turns and out-and-backs many courses include while you are tired.

Transitions

Transitions are not picnic sites, so do not linger. Practise peeling off a wet wetsuit and changing for the bike, and rehearse both T1 and T2 in your mind. Keep moving the whole time, because a disorganised transition wastes more time than most athletes realise.

Nutrition

Aim for roughly one gram of carbohydrate per kilogram of bodyweight per hour from start to finish, and drink to thirst according to the weather and effort. Whether you prefer solids, gels or liquids, the rule is the same: practise your fuelling in training so your stomach tolerates it and you know how to carry and access it. If a race provides on-course nutrition, buy some in advance to test, and practise grabbing a bottle at speed without dropping it.

How far is a half Ironman (70.3)?

A half Ironman covers 70.3 miles in total: a 1.9km swim, a 90km bike and a 21.1km run. It is exactly half the distance of a full Ironman, which is where the name comes from.

How long does it take to train for a 70.3?

Most athletes need around six months of consistent training to go from a standing start to a 70.3 finish. That assumes roughly six training days a week, with most sessions lasting 60 to 90 minutes and two longer endurance sessions of two to four hours.

Can you train for a half Ironman in six months?

Yes, six months is a realistic timeline for a reasonably active beginner to complete a 70.3 safely. The key is consistency rather than intensity: building gradually, capping weekly increases at around 10%, and protecting recovery to avoid injury and illness.

How hard is a half Ironman?

A 70.3 is a serious endurance challenge, but it is achievable for most committed amateurs with structured preparation. The difficulty lies less in any single discipline and more in stringing the three together while fatigued, which is why brick sessions and steady, conversational-pace training matter so much.

How far is the swim, and do you need a wetsuit?

The swim leg is 1.9km, usually in open water, and a wetsuit is recommended (and often mandatory) for warmth, buoyancy and speed. Practise in your race wetsuit and tri-suit before the day so the fit and feel are familiar.

What is a good finish time for a 70.3?

Finish times vary widely with course and conditions, but many first-timers aim to complete a 70.3 in around six to seven hours. For a debut, finishing comfortably and within the cut-offs is a far better goal than chasing a specific time.

Reaching a 70.3 start line is less about talent and more about turning up, week after week, on the days you would rather not. As participation in middle-distance racing continues to grow across the UK and Europe, the athletes who progress are the ones who build the habit early. Pick your race, lock six days a week into your routine, and start with your next session, not tomorrow's.