What’s the difference between Masters open-water races and elite FINA or USA-S open-water races? I would argue, it’s not so much the absolute swimming speeds (1:10 per 100m for 10K, compared to 1:20 to win almost any Masters 10K), but the variability of swimming speeds.
Masters races have a much wider spread of abilities. In this year’s USMS 10K at Morse Reservoir, the top 10 finishers were separated by 9 seconds per 100m, and the winner was a full 29 seconds per 100m faster than the median finisher. What this means is, most people are swimming most of the race by themselves.
In FINA races, the spread in abilities from top to bottom is (I would guess) less than 5 seconds per 100m. What that means is: lots of pack swimming. In order to successfully break away from an open-water peloton, a swimmer will not only have to swim faster than the others in the pack, but fast enough to break out of the peloton’s draft.
As a result, elite races are characterized by 8-9K of conservative, highly tactical swimming followed by 1-2K of balls-out sprinting. In contrast, Masters races – especially those over an hour (for the winner) – more closely resemble “time trials.”
As an exhibit, here are the 2K splits (with 100m paces) from the June 2010 USA-S 10K National Championship, provided by Powerhouse Timing:
|A Gemmell (M-3)
||J Kinderwater (M-6)
|C Sutton (F-1)
||C Jennings (F-2)
These were the only four swimmers for whom all 5 splits were recorded. For the men, Gemmell and Kinderwater finished 3-6 (negligibly behind the winner), and for the women, Sutton and Jennings finished 1-2. Interestingly, the splits were almost identical through 8K, for both men and women. In the last 2K, the men seemed to find a new gear – almost 4 seconds/100m faster – while the women maintained their previous pace.