Swimming underwater during competitive swimming (Olympics)?

Question

While watching the summer Olympics I noticed during the competitive swimming, especially during the backstroke, right after they dive into the water, they swim a long distance underwater. I also noticed, while they were underwater, they did a sort of dolphin movement (undulating up & down movement) for a period of time. Why do competitive swimmers stay underwater for so long, especially after diving into the water, before surfacing and beginning their backstrokes. Also, is the underwater dolphin movement faster than the backstroke? What is the advantage of staying underwater and the dolphin movement?

Answer 1

Staying under water after your dive is called doing an underwater streamline. Swimmers use dolphin kick (also the kick for regular butterfly) during their streamlines in back stroke to help them go faster. Streamlining is actually faster than regular backstroke, because you have the momentum of your dive or flip turn behind you. Streamlining is used in all strokes, but the techniques are different. In freestyle and backstroke, the swimmer uses dolphin kick underwater until they get near the surface, and then start flutter kicking. In butterfly, they simply continue the dolphin kick into their stroke. In breaststroke however, swimmers use a pull down (which is a whole other story.) They are allowed one small dolphin kick though.  

Answer 2

Yes, there is a limit to 15 meters each time you come off the wall you can stay underwater. This is called a "kick-out" the butterfly kick motion is the faster part of swimming especially for backstroke and butterfly. I think it was in the 90s a backstroker kicked underwater for way more than half his race and destroyed the world record so this caused there a rule of only kicking underwater for 15 meters.  

Answer 3

yeah, it's faster under water, but they can only go 15 meters. any farther and they are disqualified.

Answer 4

if you dive into the water you make big splash and big waves in the water .so to avoid  this waves swimmers use  dolphin kick under water as possible as you can to increase your speed and avoid the waves .

(swimmer use dolphin kick because it,s the best in avoiding waves )