Long, steady swimming is one of the best ways to build confidence and endurance in the water, but that doesn’t mean it has to be boring. This week’s Ruth Astle’s Endurance Swim for Mortals combines longer aerobic swims with shorter repetitions to help you develop the ability to hold a consistent pace while maintaining good technique from start to finish. Whether you’re preparing for a triathlon, an open water event or simply looking to become a stronger swimmer, this session will teach you how to swim further without feeling like you’re constantly fighting the water.
Each Saturday I publish a Swim Session with three options to suit different abilities and training volumes. Option A is designed for swimmers looking to complete between 1,000 and 2,000 metres, Option B is for swimmers targeting 2,000 to 3,000 metres, while Option C is intended for those wanting a workout of more than 3,000 metres.
Before you begin, I recommend reading my article explaining Swim Intensity, as it will help you understand how hard each part of the session should feel and how to pace yourself appropriately.
Today’s Goal
The aim of today’s session is to develop your ability to hold good freestyle technique over longer distances while learning to maintain a consistent pace. Rather than swimming flat out, the objective is to finish every longer repetition with the same quality of stroke that you started with.
Workout Overview
Option A (1,900m)
- 300 WU;
- 200 Pull;
- 400 45RI;
- 4x 100 15RI;
- 400;
- 200 CD (1,900)
Option B (2,800m)
- 400 WU;
- 200 Pull;
- 400 45RI;
- 4x 100 15RI;
- 400 45RI;
- 2x 200 15RI;
- 400;
- 200 CD (2,800)
Option C (3,400m)
- 400 WU;
- 300 Pull;
- 500 45RI;
- 5x 100 15RI;
- 500 45RI;
- 2x 250 15RI;
- 500;
- 200 CD (3,400)
Why You’re Doing This Session
This is an aerobic endurance session designed to improve your ability to swim comfortably over sustained distances while maintaining efficient technique. The longer repetitions encourage you to settle into a controlled rhythm, while the shorter 100m efforts provide an opportunity to reset your stroke before returning to another sustained swim.
The pull buoy set early in the workout helps reinforce body position and encourages you to engage your upper body rather than relying solely on your kick. As the session progresses, you’ll learn to maintain your form even as fatigue begins to build—an important skill whether you’re training for pool events, open water swims or the swim leg of a triathlon.
The goal isn’t to produce your fastest swimming. Instead, you’re developing the ability to swim efficiently for longer with consistent pacing.
💡 Inspiration Behind This Session
The inspiration for this week’s session came from a YouTube video by professional triathlete Ruth Astle, titled “Endurance swim & Wednesday bike session | A week in the life on Denia camp | Day 3 with pro athletes.“ While this isn’t Ruth’s workout reproduced, watching the session sparked the idea for this endurance-focused swim. I’ve adapted and modified the structure to create a workout that’s more appropriate for recreational swimmers, age-group triathletes and masters athletes. The result is a session that captures the same endurance-building principles while remaining achievable and enjoyable for swimmers balancing training with work, family and everyday life.
What You Should Focus On
- Swim every repetition at a controlled, sustainable pace.
- Keep your body long and streamlined through the water.
- Maintain a consistent stroke rhythm from the first repetition to the last.
- Push off each wall with purpose before settling quickly back into your stroke.
- Finish each longer repetition feeling like you could have continued for another 100-200 metres.
Common Mistakes To Avoid
- Starting the longer repetitions too quickly and fading badly towards the end.
- Taking significantly longer rests than prescribed.
- Letting your stroke shorten as fatigue builds.
- Kicking excessively during the pull set instead of allowing the pull buoy to support your body position.
- Treating the 100m repetitions as sprint efforts instead of controlled aerobic swimming.
Tips For Completing The Workout Successfully
Start the first long swim a little easier than feels necessary. It’s much better to gradually build your rhythm than to spend the remainder of the workout trying to recover from an overly ambitious start.
During the pull set, focus on applying steady pressure throughout the entire underwater pull rather than trying to muscle each stroke.
Use the rest intervals wisely. Take a couple of deep breaths, glance at the pace clock or your watch, then begin the next repetition on time. Consistency throughout the session is far more valuable than extending the recoveries.
If you’re sharing a lane, be courteous to other swimmers by allowing faster swimmers through at the wall rather than mid-length.
Workout Breakdown
For the Warm Up (WU) start with 300m (Option A) or 400m (Options B & C) of mixed swimming, include a range of strokes. During the warm-up feel free to stop and stretch as needed. It doesn’t need to be a continuous swim.
The main set is a 200m (Options A & B), or 300m (Option C) rep swum with a pull buoy.
Next up is a 400m (Options A & B) or 500m (Option C) swim with a 45-second Rest Interval (RI) afterwards.
Follow this with four (Options A & B) or five (Option C) reps of 100m with a fifteen-second Rest Interval (RI) after each.
You next repeat the 400m (Options A & B) or 500m (Option C) swim with a 45-second Rest Interval (RI) afterwards. At this point Option A moves to the Cool Down (CD).
Options B & C complete two reps of 200m (Option B) or 250m (Option C), with a fifteen-second Rest Interval (RI) afterwards.
The final rep for Options B & C is another 400m (Option B) or 500m (Option C) swim.
Complete the workout with a 200m Cool Down (CD). Unlike the previous sets which have to be freestyle, the Cool Down (CD) (like the Warm Up (WU)) can be any stroke you wish to swim. You can also stop and rest after any length. I encourage you to stop and stretch during the cool-down.
After Your Swim
Before leaving the pool, take a minute to reflect on your session.
Ask yourself:
- Did I maintain a consistent pace throughout the longer repetitions?
- Was my technique still controlled during the final long swim?
- What part of today’s session felt strongest?
- What would I like to improve next Saturday?
Keeping a simple training diary with these notes can help you recognise improvements that aren’t always obvious from your swim times alone.
Want 8 Weeks of Swim Sessions Like This?
If you enjoyed today’s workout, why stop at just one?
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🏊 Foundation – Under 2,000m per session
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Whether you’re swimming for fitness, preparing for your next triathlon or simply looking for more variety in the pool, you’ll have eight weeks of purposeful workouts ready to go.
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