After reading this article, I now know the reason, based in science and a little geometry: http://www.active.com/cycling/Articles/Should-You-Stand-to-Pedal-on-Climbs.email@example.com
Bottom line is that when you rock the bike side to side, 15 degrees either way, the crank arms do more work than when you are in the saddle and not rocking the bike - approx. 7% more work - and this equates to approx. 7-19% energy expenditure for the rider. And this savings, at the top of a pretty tough climb, is very welcome!
So, the next time you are attempting a long climb with steep pitch sections or a short but very steep hill, don't forget to get off the saddle and use your arms!
2 x 50yds. kick
1 x 100yds. drill
1 x 100yds. swim
the above set should be done 3x - your choice of stroke for 2 rounds - 1 found has to be butterfly - use your fave drills
4 x 200yds. 3 of these are freestyle and 1 is IM - work the free and cruise the IM
4 x 200yds. 3 of these are IM and 1 is freestyle - work the IM and cruise the free