All around the world, long distance open water swimming races are growing in popularity. Swimmers are taking on the challenge of events from 1000m through 5km and 10km, right up to marathon swimming events such as the 34km English Channel and Catalina Channel swims.
Far and away the most popular question we're asked by swimmers training for these long distance events is how fast we think they can swim them. In fact H2Open magazine asked us to write an article exploring how to train and prepare for these events which will feature in the next edition of the magazine. Here's an interesting snippet from the article:
Swim Smooth Race Pace Estimator
The table below is our estimation of your race pace over different distances. The figures are relative to your CSS pace which you can find using the test set here. CSS stands for Critical Swim Speed, which is very similar to lactate threshold or the concept of Functional Threshold Power (FTP) if you're used to training with a power meter on the bike.
1500m = CSS pace ± 2 sec per 100m
5km = CSS pace + 2-4 sec per 100m
10km = CSS pace + 6-10 sec per 100m
20km = CSS pace + 10-20 sec per 100m
English Channel (34km) = CSS pace + 20-30 sec per 100m
As you can see, CSS is approximately your 1500m race pace. In fact if you know your current speed over a very recent 1500m then you can use this as CSS in the table above instead of performing the CSS test.
The figures in the table are only a rough guide as your ability to sustain a pace relative to your CSS depends on how fit you are, your fueling strategy and your physiological makeup. Those with a very good aerobic base will not see as much drop off in their pace over increasing distances as those with more of an anaerobic, sprint background.