Home > Swim

Go Long: Endurance Swim Training for Ironman and Half-Ironman

It's important to include some longer swim sessions into your training program.

If you’re training for an Ironman or half-Ironman, it’s important to include some longer swim sessions into your training program. Those should either cover cover the race distance or last as long as your projected completion time for the swim. You need to do this in order to develop your muscular endurance, your mental stamina and to refine your nutrition strategy.

Swim specific muscular endurance can only be improved by swim training.  Aerobic fitness has minimal carry over from your bike and run to swimming. Improving your muscular endurance will allow you to continuously  power through the underwater pull and the overwater lift for the 1,500 to 4,000 arm revolutions needed to complete a half or full Ironman swim.

You must train your mind to stay focused, positive and aware of changing conditions for the entire length of the swim.  Completing long swims can prevent your thoughts from wandering or turning to negative ideas of loneliness, pain, frustration, cold or fatigue during races.

Your nutrition strategy for the swim is less important than it is for the other two disciplines, but for those spending more than an hour in the water, this is something to consider.


Effective swim training for any triathlon distance requires setting up pacing zones, just like bike and running. Pacing can be established by doing a best-effort 400 m time trial.  This time trial will give you your approximate threshold, or Zone 4 pace. With this you can calculate the rest of your pacing from Zone 1 to Zone 5: recovery, endurance, tempo, V02 and anaerobic sprints.  Unlike time trial results achieved for biking and running, though, these swim paces should be used mainly for pool training purposes.  Open water swim results should not be used to establish pool pacing because of the myriad of conditional factors that effect open water outcomes. Doing your pool swim training in the proper zones established by a pool-based time trial will make sure your training is targeting the right physiological system.  It will also engrain the sense of perceived effort required for open water swimming, where you don’t have access to clocks, meters or monitors.

Endurance Training for Ironman

Preparing for a 3.8 kilometer open water swim is interesting because the training and racing falls into two camps.  Those that can complete the race in close to an hour are training to race a solid tempo effort. Those who take significantly longer may be aiming to race closer to an endurance pace.  Both groups of athletes need to train at both paces in preparation.

Tempo sets should be 2.5 kilometer or 50 minutes of swimming, whichever comes first. A simple example would be 12 x 200 with 20 to 30 seconds rest. Endurance sets should be 3 to 4 km in length and should be done at a slightly slower pace (2 to 4 percent) than tempo intervals. A simple example for an endurance set would be 4 x 1 km with 15 to 30 seconds rest.  This may seem like very little rest at first, but keeping the rest to a minimum will target and train the aerobic system. It may take you three to four attempts at the workout to fine tune your pacing and adapt to the short amount of rest. It is prudent to exceed 3.8 km in the main set when training in the pool. This will ensure you have enough endurance in open water when you are faced with adverse conditions,  an improperly marked course or the extra shoulder resistance imposed by some wetsuits.  You should always include a short warm up and warm down in your workouts.

In the summer months a great option is to do endurance swims in open water.  To keep your effort levels honest, and to practice pacing, you should find and mark two loops, one of approximately 300 m and one of 1 km.  You should then do tempo intervals on the 300 m loop.  Meanwhile, you can ramp up the endurance training by doing several 1 km loops without resting.  By marking out a loop, this ensures that you can keep track of pacing.  A loop means you are always training close to shore, which allows you to  hydrate or fuel when needed.  It also guarantees that you are close to home if the environmental conditions change.

For those who will be in the water for over an hour, you may consider using a nutrition strategy used by pure open water swim racers.  Open water swimmers will consume calories every 30 minutes during their long open water races. If a feeding station is not available, they simply tuck gels into their bathing suit. To eat, they either stop and tread water or flip onto their back.  Consuming gels without water may be difficult for some, so this is something you need to try and practice before race day.

Endurance Training for half Ironman

Most triathletes will complete the 1.9 km half-Ironman swim in less than one hour.  This means that half-Ironman athletes are preparing to race a solid tempo effort.  For those people finishing in under 40 minutes, race pace falls somewhere between a tempo and a threshold effort. As with the Ironman distance training, you need to practice the distance and time required to complete the swim portion of the race. The endurance sets should be between 2.5 and 3 km. For tempo efforts, progressively increase sets to 2.5 kilometers.  Recall that tempo efforts are faster than your aerobic pace and that the length of the main set does not include your warm up and warm down.


Unlike your bike and run sessions, your swim sessions can remain long and intense close to your A, or main, race.  For Ironman athletes, long swim workouts should continue to be done until about two weeks before your A race. Half-Ironman athletes should start reducing the length one to two weeks out from their A race. Why should you continue to push your swim sessions so close to the race? First, you don’t sustain the same type of muscle damage in the water as you do from running or cycling. Your muscles undergo oxidative stress during intense aerobic work, but they are not subjected to the level of direct muscle trauma. Second, most triathletes only swim twice per week and have plenty of non-swim days for upper body recovery.

To increase your level of preparation you should make sure you work in all the other elements of the swim – starts, buoys, passing, drafting, waves, current (can be simulated with parachute or endless pool) and crowds.  By practicing these items you will be better able to regain your focus, form and rhythm when it is disrupted in a race.

Ensuring that you have done race appropriate endurance swim training is key to feeling prepared and it is critical to a successful swim. Making sure you train your mental strategy, technical open water elements, pacing and even your nutrition plan may put you ahead of your competition.

Ayesha Rollinson is a professional triathlete and swim coach from Toronto.