iheartbenben

This was posted in road, but to no avail.

Sprinting, or general power out of saddle, comes in two forms to me and the riders I casually associate with.

Stiff sprint - No 'wobble' in the bars, mostly bicep power pulling up on the hoods/drops.

Swerve sprint - Pronounced wobble in the bars, and amplified 'sway' of the frame due to this. Pressure more even, if not pushing slightly down on the hoods/drops.

Any insight into WHY we do this, when to do this, and to what end these means come to, would substantially help my form at this point.

vision646

I've always wondered about the reason why you see so many professional riders who wobble as they sprint, is it because they are tired and their form has suffered or is it on purpose (this is my guess). I just can't figure out why.

iheartbenben

Me either, as well as the 400 plus average viewers of the road forum (though this means little). What do you think personally, Vision? I have yet to get any solid answer or lead on this topic. It took me over two years to finally start inquiring about it.

I'm waiting for Pcad to drop the bomb, but since I tickle people and have a general sense of humor, I'm likely to be ignored by the fashionistas.

vision646

My intuition is that the "wobble" helps generate some added power using your other muscles. I've watched many in the pro peloton do it and you can see their arm muscles flexing significantly. Since your arms muscles are used so much less than your legs it might help add some power while not fatiguing your legs anymore, now the question becomes is this good technique or not. Does it use significantly more energy than just using your legs? Or perhaps it requires a lot of energy to keep yourself "stiff" so its better just to go with the flow?

black_box 

Most people can do a few pullups, then on the last one or two they get half way and just sort of hang there, "pulling" but not moving. Perhaps it's the same mechanism just with the legs? you have enough energy in the legs to "hang" but not enough to push/pull all the way through?

Carbonfiberboy 

A good sprint doesn't "wobble." The tires should move in a straight line. Steering from side to side robs energy and travels more distance. Not that one can't win with a wobbly sprint, but most of us try to sprint as straight as possible. It's always best to take up as little room as one can, less chance of getting hooked.

The other part of your question, I think, is why sprinters rock their bikes. There are two reasons. One is that you want your downstroking foot to be as close to over your contact patch as is convenient. This seems to create a more efficient energy transfer, or maybe it just takes less effort to hang onto the bike. OTOH, rocking the bike takes some time and energy too, and when you're sprinting at over 100rpm you don't have time to rock the bike very far.

The other reason for rocking is to add power to the downstroke. Imagine that your downstroke on the right side is in its last quadrant. Your bike is rocked to the left. Your next downstroke will be with your right foot (duh). As you begin that downstroke, you're going to powerfully rock the bike to the right. That rocking will, in effect, raise the left pedal toward your CG so that you get a slightly longer, more powerful downstroke out of it. That's the reason that sprinters have much more powerful upper bodies than other riders. They in effect row their bikes toward the line as well as pedal them.

Sprinting like this uses a different timing for the rocking than one would use while doing rest strokes on a long climb. Not being on my bike while writing this, I'm not quite sure how to describe it, but I think when rest-stroking the bike comes across earlier so you're not prying it over against the force of the downstroke. That's not restful or efficient for climbing.

You just have to go out and play with it to get the feeling for the timing of the rocking motion, both when sprinting and when climbing. If you and your bike are well balanced and your fork has the right rake and trail, you should be able to stand and pedal while riding right on the fog line. That's a good test.

gregf83 

You asked and this question was answered in the road forum. The rocking back and forth is a by-product of a powerful sprint. If you see someone dead straight they're pedaling at a very high cadence or low power.

If you want to improve your sprinting technique go the road racing forum and have a look at interval training sticky. There are a number of intervals, spin-ups which will help your sprint power.

Nick Bain

I think I and they rock their bikes because its natural and here is my well thought out reason why: when out of the saddle we keep our bodies still and rock the bike because if you want to keep your bike still then you are moving your body and wasting energy an losing aerodynamic form. More specifically when you rock the bike it is due to pedal stroke. You rock the bike because it gets your leg closer to the power stroke faster and more efficiently. If you were keeping your bike still when out of the saddle then you would be bouncing your bum, torso, and head up and down to get your feet to the top of the power stroke. Also if your moving your body then you are not able to maintain a constant aerodynamic position which is made more possible by moving the bike from side to side and keeping your body/ torso still.

I just pulled this out my bum but I am 99.9% sure of this. Now off to watch sprinting videos to see that I AM right.