Elite swimmers are built like Greek gods. Except without hamstrings.
Their quadriceps are massive. And, of course, their lats, deltoids, triceps, abs and pecs are ripped to the max. Yep, even the women.
But other than the random breaststroker who needs some leg contraction, they have withered, almost nonexistent hamstrings. The sport does not call for their extended use. Runners have hamstrings. So do football players, basketball players, tennis players, wrestlers, joggers.