Swimming Workouts: Interval and Heart-Rate Sessions for the Pool

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The benefits of swimming are numerous, but the trouble with pools is they make it all too easy to stick to the same pace and number of lengths each session. Not only is that boring but, worse, it won’t make you any fitter or faster.

Introducing training methods such as intervals and heart rate sessions will help you develop greater speed, endurance and technique in the water, especially essential if you’re training for a triathlon. You’ll also be able to structure your sessions to fit easier workouts into your training programme, a change that will give your body the time it needs to recover and become stronger. Here are the key sessions you should include.


Interval sessions are periods of high-intensity swimming punctuated by periods of recovery and should form a substantial part of your training. They allow you to fit more challenging work into your session than if you tried to do it all continuously. The aim is to raise your heart rate during the high-effort segments so your body gets used to working at higher intensities and adapts to deal with this added workload. There are several ways you can adjust the structure of your intervals to keep them fresh and make them progressively more difficult.

Distance: You can increase the distance of the interval and train yourself to swim further at the same high intensity. For example, you could start in week one of a programme by swimming 4x200m and increase it each week so you are doing 4x300m in week four.

Time: You can vary the time you have to complete an interval so that you swim a set distance in a progressively faster time. You could start by giving yourself 2min 30sec to swim 100m in the first week of your new programme and increase the pace so that by the fourth week you cover the same distance in 1min 45sec.

Number of reps: As you improve you can increase the number of reps you swim during a session. Say you start by being able to swim 5x100m front crawl in your first session before reaching exhaustion. By week four you should aim to complete 8x100m.

Aim time: These intervals are structured so that you have a total interval time and an ‘aim time’ by which you want to complete a set distance. If you have a two-minute interval with a 1min 45sec aim time, you would have 15 seconds’ rest. You can then reduce the aim time to swim at a faster pace but with more rest repetitions.

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Heart-rate sessions

Instead of being based on time, these sessions are distances swum at a target heart rate, which will be a percentage of your maximum heart rate (220 minus your age). They build endurance and allow you time to refine your technique. An example of this session would be to swim 8x100m at 80% of your maximum heart rate with a resting period interval of 60%. This means your heart should be at 80% by the time you finish 100m and then you rest until it returns to 60%.

Negative splits

These sessions are great for improving your ability to finish a race strongly, because the aim is to complete the second half of the workout faster than the first. So in a 400m session you’d aim to swim the final 200m quicker than the first 200m.

Build swims

In a build swim you gradually increase the pace and effort over a set distance. This session type is useful if you want to improve your ability to control your pace, which is vital in triathlon racing. As you tire, your instinct will be to slow down, but these sessions build discipline to stick to a set pace and then push yourself harder. A typical build swim could be 6x200m with the first two lots of 200m at 60% effort, the next two at 70% and the final two at 80%.

Broken swims

These are swum faster than race pace to improve raw speed. You try to beat your best time for a distance by breaking it into chunks. So, in a 25m pool, if your best time for 100m is 80sec you would aim to complete each length in less than 20sec, with a 5sec rest between lengths.