How to train for & race a 10km marathon swim

17th September 2015

Thanks to the Olympics the 10km marathon swim is set to attract ever-increasing numbers of entrants, including plenty of first-timers. Swimsmooth’s Paul Newsome draws up a training programme aimed at 10km newcomers and ambitious swimmers alike.

The 10km marathon swim is now an Olympic event, and at this year’s London Games takes place in Hyde Park’s Serpentine, and is one of only a few free-to-view events. It should therefore attracted thousands of spectators and inspire many to attempt the distance themselves.

How to train for & race a 10km marathon swim2

While 10km might seem significantly more achievable than, say, swimming the English Channel, good preparation and the right training is still absolutely essential for not only being competitive in your age group but actually completing the distance. Here we off er a best-practice guide for preparing for your fi rst, or fastest, 10km open water swim – drawing inspiration from many of the professionals we are fortunate enough to work with over here in Perth, Australia.


The key to sensible 10km training is to ensure you don’t go at your programme in a mad panic to get yourself fit ‘yesterday’ – a weekly progression increasing volume by 10 per cent is what you need to aim for. For those currently swimming 2-3 times a week for up to 3.5km at a time, allow yourself 16 to 20 weeks preparation time. If you swim four or more 4km-and-above sessions per week – let’s call you a ‘competitive’ swimmer – your lead-time should be around 12 weeks.

Here’s how a 20 week programme might look, from a progressive perspective. (Competitive swimmers can pick up this programme in week eight). Note: this is a guide only, but it is a good baseline from which to work.


Establish Consistency
These first two weeks are quite light and designed to get you rolling your arms over and establishing factors such as how your training will best fit in with daily routines. We recommend that you take up to eight sessions before you start to feel like you’re ‘training to train’, as opposed to just going for a swim.

It’s important that you schedule a lighter training week every three to four weeks, where volume is reduced but a semblance of intensity is maintained. Failing to do this can result in burn-out, staleness, injury, illness and simply a lack of adaptation to the work you are putting in. With rest comes strength.

Stroke Economy Development
During this phase you will be in the swing of your routine and looking to ensure that your form and technique in the water is sound. Enlisting a coach to undertake video analysis and provide useful stroke correction tips is highly recommended at this stage. You can also start to build up your interval distances at critical swim speed (CSS) pace plus between 6-8 seconds per 100m. Think of this as the pace you’ll eventually swim during your 10km attempt. (For details on how to calculate your CSS pace visit Making one of your weekly swims slightly longer than the others at this stage with intervals ranging from 600m and above is a great way to incorporate both form and endurance into a session.

Threshold development
Of your four sessions per week in this block, aim to make one in the first two weeks and two in the final two weeks a CSS paced session. Here you’ll be working on getting faster at CSS pace. Aim for a speed increase of between 0.5-1.0 per cent at CSS pace per week. CSS sets include: 15 to 20 x 100m, with 15s rest; 8 to 10 x 200m, with 20s rest; 4 to 6 x 400m, with 30s rest; and 3 to 5 x 500m, with 40s. Aim to hold great form throughout.

How to train for & race a 10km marathon swim3

Sustained Endurance
It’s a common mistake to do too much long, slow swimming early on in a training programme and then struggle to pick the pace up as you get closer to your race. By developing your CSS pace in the previous block of work you can now look to start swimming longer sets at just a touch faster than 10km pace. Identifying your 10km pace is always tricky, as all manner of things can affect what time you swim on race day, including conditions, feeding strategies, and how straight you swim. It’s advisable to do a 4km continuous pool swim in week 13 at your best possible pace and then to calculate your average pace from this. The result will be an ideal pace to train at for your longer weekly sessions. Try to do one long, continuous swim a week at this pace, and from week 13 add an additional 800m to the distance each week, reaching 8km by week 18.

Fine Tuning
Your weekly volume is now starting to taper off, but don’t let your intensity drop off too much yet. During this phase you can ensure factors like your planned race attire, race and nutrition strategy are all in place. Maintain a couple of longer, continuous swims of 6-8km and visualise yourself actually doing the race while you do so. Now is the time to make any changes, not the night before or even during the race.

Your final week should be relatively steady, with a few little pickups at CSS pace, but preferably no more than 1,200m in a given session. Get some good sleep in and eat and drink well. Again, don’t make any drastic changes in the lead-into the event. It is worth highlighting here, that the best programmes are balanced, and contain a good mix of technique and specific fi tness work throughout – albeit with a subtle change in focus as you move through the plan.


Ideally you’ll be consuming 0.8 to 1.0g of carbohydrate per kg of body weight per hour and 500 to 800ml of fluid per hour in sessions longer than an hour. This ensures you’re putting back into your energy reserves what you are taking out, and will allow you to finish strongly and recover quickly.

During the event itself you might be restricted to fuelling once per lap on a typical four-lap course, which, depending upon your speed, could mean a fuel stop every 30 to 60 minutes.

On some of your longer practice swims in the open water set up a similar lapped course to allow you to fuel as you will in the race. This way you can work out what works and what doesn’t in the race.

Drafting or ‘slipstreaming’ off another swimmer can save you up to 38 per cent of your energy expenditure if done correctly. This could get you through your first race in a much less fatigued state, and be the difference between winning your age-group or being out of the medals. Drafting is a skill like any other, and requires practice and due diligence, so be sure to add some structured time to your routine to go through this with friends.

Drafting can be done at around 50cm behind another swimmer, or directly to their side with your head positioned at about waist level. If choosing the side-drafting option, aim to breathe in towards the swimmer and not away.

Race Suit
In many 10km events you’ll have the choice to swim with or without a wetsuit. Depending upon your natural buoyancy wearing a wetsuit could save you 2-3 minutes per kilometre, which over 10km is significant.

Although the hardcore open water swimming fraternity may frown upon your use of a wetsuit, if it is your first 10km event we recommend that you use one. When it comes to your health and your safety, a wetsuit might just make the difference.

The best way to race a 10km event is mimic what you’ve done in training – with perfectly even splits, holding a consistent pace. Avoid setting off too fast and resist energy-sapping surges during the swim.