Originally Posted by Matthias99
I literally have no idea how you could post that video and still disagree with me, since he is saying the exact same thing I'm saying. He talks about pressuring the bike with his legs on the downslope of the landing -- ie, the 'downhill' side. That's where "pumping" with your legs causes you to speed up, because at that point the reaction force from the surface is pushing you forwards (although he doesn't say it quite like that, that's why it speeds you up). See the illustrative freeze-frame at 0:39. He's extending on the 'downhill' side to propel himself forwards!...
Let's try this slowly.
You can pump a transition, using some combo of parametric and driven oscillation, as I have noted multiple times. The landing of those jumps, and the takeoff of those jumps, each represents a transition. This is the same as the U shape of a halfpipe (two transitions, one on each wall, separated by flat bottom) or skatepark.
You can pump each transition. You can pump going down a transition, just as you can going up a transition. For instance, a skater dropping into a halfpipe, IF he wants to go faster than a "passive" drop would have him go, will drop in crouched, and then extend/drive through the transition to generate extra speed. He then will again crouch, and extend/drive through the next transition on the next wall before he goes up to the lip of that wall. Real simple, and the sequence is the reverse of what you are suggesting.
Extending/driving into the transition or, in the case of moguls, the face of an approaching bump, does NOT slow you down, it speeds you up. In the real world, it is called pumping. This is so if you hit just one transition (a speed bump on a bike, the lip of a small jump in the terrain park at a ski area, or a quarterpipe on a skateboard, or a bermed corner on a MTB) or two transitions (for instance, a halfpipe at a ski area, or a skatepark, or a steep, narrow gully at a ski area).
Here is a simplification, http://www.exploratorium.edu/skateboarding/trick04.html "a skater first drops down into a crouch while traversing the more-or-less flat bottom of the U-shaped pipe or bowl. Then, as she enters the sloped part of the ramp or bowl, called the transition, she straightens her legs and rises up. By raising her center of mass just at the beginning of the arc, the skater gains energy and thereby increases her speed." Note the skater increases speed, rather than slows down. Also note that I said this was a simplification, which it is.
You, by claiming that it slows you down, have in fact inverted what happens. And also misunderstood the video I linked. Your claims that "Coming in prewound and extending on the 'uphill' side slows you down..." , and " that [extending on the uphill side of a mogul] WILL decelerate you ..." , " are directly counter to what actually happens. When a skier, bike rider, or skateboarder DOES, in the real world, come in "prewound" and then extends on the "uphill" side of a transition, they end up going faster.
This is why the timing of the extension utilized by bump skiers is so important. Full extension needs to happen before the trough, so that the legs can then be released into absorption on the face of the next mogul. This is because bump skiers AREN"T generally pumping for speed, they are absorbing. However, if you do pump for speed in flat bumps at a ski area, you will use pretty much the movement pattern that Matt99 has just claimed slows you down.
Get to a skatepark, Thomas, as another poster on here already said Or a pump track. Or a bike park. Or, ski some bumps.
Edited by CTKook - 9/9/13 at 1:13pm