Why Do Sprinters Swing the Bike Back and Forth?
 

A cycling coach recently told me that I need to reduce my hip rocking while pedaling. He said that it is more efficient to keep your hips steady, rather than allowing them to rock up and down. To me, it feels actually more powerful to allow my hips to rock, rather than forcing them to stay steady.

In trying to understand this from a physics/engineering standpoint, consider this. When you stand up to pedal, as when sprinting, doesn't it feel more powerful to allow the bike to rock back and forth underneath you? Isn't this rocking of the bike the same as a corresponding rocking of the hips while seated?

Here's another thought experiment that is related. If sprinting while allowing the bike to rock results in greater speed (which must be true, since all of the pro sprinters do it), what happens when the bike is mounted in a trainer? With the bike fixed vertically like that, so that you can't allow it to rock, but if you want to generate maximum power, it seems to me that the only way to do so is to allow your hips to rock instead.

Any thoughts?

go to Carmichael's website and get his sprinting workout DVD. They are working out on trainers and it's all explained there.

Cavendish, McEwen, and Alijet all rock their bikes. So did Cippolini. They are pulling and pushing for greater speed, but that's also explained in the DVD. Proper positioning, arms as well, in there.

Fixed.

Rocking hip means you are using more muscles to stabilize your body than necessary. This leads to fatigue, and eventually pain in places other than your leg muscles from the stresses of being stretched and compressed in a very unnatural position.

It also looks bad.

The power you must produce in a sprint lasts for 15-30 seconds. For most of the ride you need to conserve energy and pedal as efficiently as possible. I mean, would you ride for 2 hours out of the saddle?

Who doesn't? HTFU

When your cadence is already at max, the only way to put more power to the pedals (short of strapping your butt to the saddle) is to have them come up toward your feet as they go down.

Keep in mind that proper sprinting technique isn't just about your legs or hips. You can generate more power by using your upper body by pushing and pulling down on the handlebars.

Correct.

And they're not intentionally swinging the bike back and forth . . . . it's swinging because with each powerful standing leg-thrust the bike wants to veer to that side. It's the arms & shoulders that must keep the bike from falling over. Then the whole scenario switches to the opposite side of the bike with the opposite leg-thrust.

Yes, it consumes a lot of energy which is why you only stand to sprint when you have to.

They didn't have DVDs in my day, I had to learn this stuff from others. :)

When I sprint, I'm not using my arms to stabilize the bike....

I actually forcefully push and pull on the bars which in my case transfers more power to the pedals.

When I'm sprinting to close gaps or respond to accelerations in the peloton, I'm in the drops and standing, but I conserve energy (or btter yet my legs) by spinning an easier gear and NOT using my upper body.

Ok so I quickly scanned the thread and didn't see the answer so I apologize if I am repeating. The thing to realize is that there is a difference between POWER and EFFICIENCY. You can do a lot of things to generate maximum power for short periods of time that aren't very efficient. For general riding, efficiency is more important. For racing, sometimes maximum power is more important.

I believe you and your coach are talking about two completely different things.

When TTing or climbing, yes, it is best to have a completely still upper body. Don't rock at all. You're less efficient when this "rocking" occurs.

When sprinting, put your entire body into it. Use every muscle you have to propel the bike forward. You don't have to worry about efficiency.

There is a obviously a difference between generating maximum power in a sprint and in a 20min interval.

I remember figuring this out within a couple weeks of ditching my training wheels.

So it can cause back pain? That would be a great reason to avoid it, to me.

Honestly, I don't care how something looks. I'm wondering if this could be an example of an old concept that people accept as being true, just because it's always been taught. Kind of like the old batting tip that you still hear yelled out to young hitters from their dads, "Keep your weight back!" Bad advice, but it still gets repeated generation after generation.

And I'm not intentionally rocking my hips either. In fact, I have to intentionally not rock my hips.

I guess you're just smarter than I am. Congratulations.

Having re-read all of the replies, I agree that hip rocking might be a source of lower back pain. I'm still not convinced that it is less efficient than riding with still hips.

To those who separate efficiency from power, I would argue that power and efficiency actually go together. Power is what moves the bike. Efficiency is a measure of how well a given amount of power translates into forward speed. I think what you are actually referring to is the difference between aerobic and anaerobic power output in the body. Correct?

I guess I see it this way. Put a world-class sprinter on a trainer. Have him stand up and practice a sprint, using the same effort level as in an actual race. Since the bike is fixed vertically, one of two things will happen. Either he will rock his body back and forth, or he will keep his body more still, but he will put out less power than normal.

Here's another way of looking at this question. When you watch cycllists climbing (while seated), you often see their heads bobbing right-to-left. Why is that?

(Sorry for all these odd questions. In school, teachers used to tell me that I asked questions that nobody else did. I considered that a compliment. I still do. Can't help myself, I guess.)

Maybe you just need to adjust your saddle height.

Thanks for the idea. The affore-mentioned coach tried that right away though, and the hip-tilting didn't go away. If I remember correctly, he said that tilting could be a sign that the seat is too high, but that wasn't it in my case.

Incorrect. Efficiency is how well your body generates the power. The same power moves your bike forward regardless of how efficiently you generate it. It is just like buying bike components. The most efficient thing to do would be to buy the components that offer the best value for their cost. Or performance for their cost if that is your objective. However, after a certain point you reach the diminishing point and the cost becomes much higher for additional gains. Also think of standing while climbing. Standing is generally regarded as less efficient, in that it takes more "effort" to generate the same power. However, you can usually generate more power standing. In the case of a sprint, you are using more of your body to generate more power, but this has a cost and you will not be able to maintain it for very long. Aerobic vs. Anaerobic is not relevant. You would find the same thing if you got out of the saddle and "sprinted" rocking the whole bike side to side even if you were not at an anaerobic effort--that you just can't maintain that as long as you could if you sat down and spun smoothly at the same level of effort.

Efficiency is as efficiency does. Don't swing your bike & I will, see who is faster. I dont know the ergonomics or physiology behind it. But you can use more of your body arms-back-ass when you are a little loose on the bike.

then it's your pedal stroke, your hips should not be rocking back and forth when you are on the saddle. Wait...are you mashing? if so then your probably moving your entire body so you can put enough force on the pedals and in doing so you are making yourself less efficient. Maybe try spinning a larger gear and see what that does for you. You should also consider getting rollers, those will help smooth your pedal stroke.

To its easier to describe than see.

The great riders (meaning the fastest ones) never look like they're fighting the bike. Instead, both rider and machine look effortless as they move along, even sprinters in full tilt.

Then there's the rest of us who look like a monkey taking indecent liberties with a football. There's herky-jerky movements, we're pedaling squares with tense shoulders and generally look like we're in a war of wills with our machine.

You want to be more the former than the latter.

Rocking hips make you look like the monkey.

As others have said, just because something does produce more power over short intervals does not make it more efficient. Yes, this novel hip rocking idea may work for you for 20 seconds or 20 minutes, but during a two hour bike ride you're going to be expending a whole lot more energy (with muscles that probably shouldn't be worked that hard) to accomplish the same goal.

Take it from someone who had a bad fit, got into some bad form habits and now has a lifelong chronic injury because of it, doing it different than 130 years of ad-hoc rider research doesn't necessarily mean its better.

Thanks! Great point about the 130 or so years of research. I'm guess I'm just trying to understand the "why" question, so that I can more enthusiastically embrace the "how" of it all.

Any comments on my question about the head rocking from side-to-side?

Thanks again.

Thanks for reminding me about the rollers. A co-worker recently suggested the same thing, but I forgot about it until you reminded me.