Train for the extreme: how the pool can prepare you for your toughest open-water swims

Built in the pool, proven in the wild: How to use the swimming pool to prepare for extreme outdoor swimming. Words by Nicola Butler.

Cold water. Darkness. Waves. Wind. Long distances. When you’re preparing for an extreme outdoor swim, the swimming pool might seem like the least extreme place to train. In reality, it could be where your performance is built.

Maybe the conditions deteriorate, your shoulders begin to ache, or your feeding hasn’t gone perfectly. The next landmark seems no closer than it did 20 minutes ago and maintaining your stroke suddenly requires conscious effort. Whether your goal is a 10km marathon swim, an English Channel-style crossing, a cold-water challenge or an ultra-endurance event lasting many hours, success isn’t built entirely in open water. A huge part of it can be built between two walls. The swimming pool provides something the ocean never will: control.

Distance, pace, intensity, recovery and technique can all be measured. Used intelligently, that makes the pool one of the most effective training environments available to an extreme swimmer who loves outdoor swimming.

Build an engine, not just a weekly distance

Endurance swimmers can become obsessed with kilometres. If the event is 10km, the instinct is to swim 10km. If the challenge lasts six hours, surely you need to keep swimming for six hours? Sometimes long swims are necessary, but repeatedly covering enormous distances isn’t automatically the best way to develop endurance. Pool training allows you to break a huge physical demand into manageable, measurable pieces.

Instead of simply swimming 5km continuously, for example, try: 10 × 500m with 20–30 seconds recovery.

• Suddenly you can monitor your pace across every repetition.
• Did number eight look like number two?
• Did your stroke rate change?
• Did your technique deteriorate?
• Could you maintain your pace without dramatically increasing your effort?

As your endurance develops, increase the repetition distance or decrease the recovery:
Progress from 10 × 400m to 5 × 800m, 4 × 1,000m or 2 × 2,000m.

The objective is not simply becoming capable of swimming for longer. It’s becoming capable of swimming well for longer.

The indoor endurance builder for outdoor engines

5 × 800m freestyle
Rest: 30–45 seconds
#1 Comfortable aerobic
#2 Target endurance pace
#3 Target pace + sighting
#4 Slightly stronger
#5 Hold target pace under fatigue
Goal: Keep the difference between your fastest and slowest repetitions as small as possible.

Know your all-day pace

Extreme swims punish enthusiasm. The first kilometre can feel fantastic. Your arms are fresh, adrenaline is high and swimming slightly faster than planned seems effortless. Several hours later, you may pay for it and environmental conditions can change. Pool training gives you an opportunity to develop exceptional pace awareness. Start using the clock. If you believe you can maintain 1:40 per 100m, don’t simply swim ‘roughly’ at that speed. Learn what it feels like.

• Can you swim 20 × 100m and repeatedly hit 1:40 without constantly looking at the clock?
• Can you maintain the same rhythm over 400m?
• Can you still recognise that effort after 5km?

The best endurance swimmers don’t simply have speed. They understand effort.

Make technique your superpower

Use drills to improve specific elements of your stroke, but more importantly, learn to maintain those improvements while tired. One particularly useful approach is fatiguereset swimming. Swim 200m strongly followed immediately by 100m where the only objective is technical perfection. Repeat six to eight times.

You’re teaching yourself something extremely useful: how to recognise a deteriorating stroke and reset it. Several hours into an outdoor swim, that skill matters.

The pool builds the swimmer. The outdoors builds the adventurer

You cannot completely prepare for extreme outdoor swimming indoors. Nor should you try. The unpredictability is part of what makes open water swimming extraordinary. The sea doesn’t care what pace you normally hold. Lakes don’t provide lane ropes. Rivers don’t give you a wall every 25 metres. Conditions change, and eventually you have to meet them. But you can arrive incredibly well prepared – use the pool to build your aerobic engine.

Develop strength and efficiency. Learn your sustainable pace. Practise feeding. Refine your stroke until good technique becomes automatic. Learn how to maintain that technique when your shoulders are tired and your brain is telling you you’ve had enough.

Then head outdoors – practise dealing with temperature, conditions, navigation and uncertainty in an appropriately managed environment. When the two forms of training come together, something powerful happens. You stop simply hoping you’ll be able to complete an extreme swim. You start knowing you’ve prepared for it.

Top tip! Swimming in the sea with choppy or large waves?

The single top tip for swimming in waves is to shorten your stroke and increase your stroke rate (cadence) to punch through the water. In calm water, a long, gliding stroke is highly efficient. In waves, however, a long glide makes you unstable. The moving water will toss you off balance, stall your momentum, and cause you to sink between wave crests.

• Lift your elbows high

• Breathe to the leeward (downwind) side: only breathe away from the incoming waves

• Sight on the crests