Interval Training for Swimming – Issue #5

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Training for a distance swimming event is very different from training for a run or cycling event. When training for a marathon, for example, you would start out with short runs, and gradually increase your mileage each week as you build up endurance. You may work on sprints to increase speed, but overall the goal is to run further or for a longer period of time to get ready for the event. When training for an open water swim or triathlon, you must do much more than just swim more laps each time you hop in the pool. Interval training for swimming becomes essential, especially when it comes to triathlon.

First of all, you have to understand that racing any distance over about 200 yards consists of using a combination of aerobic endurance and anaerobic endurance. Aerobic means ‘with oxygen.’ During aerobic work the body is working at a level where demands for oxygen and fuel can be met by the body’s intake. Anaerobic means ‘without oxygen.’ During anaerobic work, involving maximum effort, the body is working so hard that the demands for oxygen and fuel exceed the rate of supply and the muscles have to rely on stored reserves of fuel. Anaerobic training is generally attained at around 75% of maximum heart rate.

Interval training is used to describe the system of multiple repeat swims used in most swim training programs. An example is a set of 10 repeats of 100’s at 80% effort with 10- 20 seconds rest between swims. The best way to improve aerobic endurance is through short rest periods. The most effective aerobic fitness training occurs when a swimmer begins the next repeat with their breathing and heart rate still considerably elevated from the previous swim. This condition causes physiological systems to remain overloaded for the entire set of repeats, including both the rest and work periods.

Example of a typical aerobic set: 10 x 100’s on 1:40 interval

This means swimming ten 100-yard swims within 1 minute, 40 seconds, including rest. If you finish the 100-yard swim in 1:20, you get 20 seconds rest. If you finish in 1:35, you get 5 seconds rest.

Anaerobic fitness is also an important part of your training, although it should not be emphasized often when preparing for an Olympic distance, half ironman, or ironman- distance triathlon. Effective anaerobic fitness improvement is done in two ways. One is short sprints at race pace with short rest periods, which allow your body to become used to lactic acid buildup. The second is through speed work: short sprints with plenty of rest.
Examples of typical anaerobic training sets:

1) 20 x 25’s on :25
2) 20 x 25’s on 1:00

In set #1, you are training your body to finish a race strong, with lactic acid buildup. This type of set should not be done more than once per week.

In set #2, you are building up your speed. For distance athletes, this is only needed about once every 2 weeks at the most.

Keep in mind that no training should be done at the expense of technique! There is never a point where you should cut drills completely out of your workout. If you are a true beginner, take a few lessons before you begin your training program. With the right instructor this can be one of the most valuable things you can do in training for a triathlon. If you need help finding a coach in your area, check out our directory at

For a program designed to prepare you for an Sprint Distance (or shorter) triathlon, check out the Sprint Triathlon Training.

STROKE TIP #5: The best way to measure your training intensity is to count your heart rate immediately after each swim. You can estimate your heart rate by counting your pulse rate for six seconds immediately after each swim. Add a zero to this count, and you will have your approximate exercise heart rate per minute.