Breaststroke

Finally we start to learn swimming. We watched video of breaststroke at beginning of the class. I was a little bit late, but watched most of the part. I am a pretty good breaststroke swimmer, and my first style of swimming is breaststroke. I don't have problem in most part, but only my endurance is not very good, not endurance of casual breaststroke swimming, because I don't feel tired at all if I don't have to speed up. My problem is keep high speed for long distance, say, 500 yards, in breaststroke. I am going to train myself on this.
Some good breaststroke video clips:
first,
second,
third.

Brendan Hanson World Record Breastroke:
first,
second,
third,
forth,
fifth.