Each swimmer swam through 25 yards of the guar-thickened water, then took a break and swam the same distance in another pool One swimmer said, "Swimming through that guar was exhausting! By the time they put me in the clear water I could barely move my arms and legs. I'm amazed that my times were even close -- If I'd swum in the water first, I would have gone 10 times as fast! But hey, I guess that's science."
You can always find a totally incompetent scientist somewhere, but I rather suspect that they had some of the swimmers swim in the guar first, and others swam in the water first.