Flexibility and bike fit. (1)

Triathlon Forum
1

I have to admit that I’m terribly confused. I’ve been hearing two different things about bike fit which seem to be completely contradictory.

  1. I keep hearing that for a correct fit you want a 90 degree hip angle. If that’s true, then you have to rotate your entire body forward in order to move into a lower, more aero position.

  2. I also keep hearing that to get lower, you need to be more fit and more flexible. But this doesn’t make any sense at all to me. If you’re supposed to maintain that 90 degree hip angle, then your body angle would remain the same. Why would you need to be any more flexible?!?

Please help. I’m puzzled.

2

a 90 degree hip angle using what as a fulcrum, and what as the distal points?

3

I was using these two articles as reference.

http://www.slowtwitch.com/mainheadings/techctr/bikefit.html

https://www.bikesportmichigan.com/features/exisitingfit.shtml

4

I’ve been doing a lot of reading about bike fit also and I read through the two articles you posted. I may be totally off base here (and if I am, someone more knowledgeable please correct me) but I’ll try to answer your question as I understand it.

It is ideal to keep your hip angle and shoulder angle–as defined in the articles–at 90 degrees no matter what your seat angle is. Then, while keeping these angles consistent you rotate your body in a clockwise fashion around the bottom bracket to increase your seat angle. When you do this, you will likely have to move your saddle up and forward and move your handlebars down. This puts you into the aerodynamic position (steeper seat angle, lower handlebars).

Now, to your question about flexibility. I think you are correct from the waist up but are forgetting about below the waist. If your hip and shoulder angles stay the same no matter your seat angle then you shouldn’t need any extra flexibility in your lower back. But, when you make your seat angle steeper, you are changing the angles in your lower body, particularly your leg extension angle. As your seat moves forward, your leg extension angle is going to become more obtuse. See how in the BikeSport article their leg extension angles increase slightly in their “after” pictures. I think this increased angle is going to require increased hamstring flexibility. Now that I think about it, you may need a little increased flexibility in the muscles in your lower back as well to achieve these positions because the hamstring muscles and lower back muscles are related to each other as they connect to opposite sides of the pelvis (this is why hamstring stretches can help alleviate lower back pain).

So, that was a really long-winded answer and may be totally wrong but at least it’s an attempt to explain why these two concepts are not contradictory. Any other suggestions are highly welcomed.

5

look at our current articles on the site about bike fit, in the bike fit tabs.

6

I’m an idiot.

I’ve been bending at the waist, cutting off my chest, and restricting my ability to breathe. No wonder, I never managed to get the fit right on this bike.

Today, I rotated my entire hip instead and all of my problems were instantly fixed. It was like night and day.

And in retrospect, it’s obvious.

Doh!