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Wednesday, April 8, 2009

Talkin' bike seats

I mentioned in my last post that, for the average woman, and ideal seat design would be wide in the back to support the wider ischial tuberosities, but then needs to quickly narrow to avoid compressing the tissues distal and lateral to the sit bones. 

This narrower space between the femur and sit bones that we tend to rest (which ends up being the proximal hamstring -- medially the semi-membranosus and laterally the biceps femoris) is not the only reason for this saddle shape.  The woman's sit bones are oriented more in the frontal plane (more side to side) than a man's.  The male sit bones are set more in the sagittal plane (front to back).

When you factor in the natural translation of the hips and pelvis downward at the bottom of the pedal stroke, you can visualize that the male sit bones can more readily follow this path of movement -- sort of like a knife blade slicing through the dirt.  The female sit bones can't move as easily in this path -- imagine running the same knife through the dirt now turned to it's side a few degrees, like a plow.  The amount of shear force (or at least the potential for shearing) is much greater.

Essentially, all the angles of the pubic and ischial rami (the structures that form the "loops" on the bottom of the pelvis, and that we sit on) are steeper and sharper and because of this, less contact with saddles is probable.  I think this is the reason women often struggle with saddles -- more contact and shear forces -- and not just the fact that they have wider sit bones.

Saddle position

Of course, the right saddle is nothing without it being fit in the right position.  Many cyclists are on saddles they are unhappy with, but the reason is that they are not sitting on the part of the saddle that is meant to be sat on.  Most are scooted too far forward, even to the point where the sit bones don't rest on the saddle, but rather the saddle is squeezed in between them and the rider is resting more on their soft tissue -- this is a problem, obviously.  A huge mistake I see all too often is having the saddle tilted down --- yes, even a little is generally not a good thing.  

A bike seat needs to be in the right place fore and aft so that the sit bones can contact the wider, more cushioned portion of the saddle, and then it needs to be level so that the sit bones can rest on it.  If you aren't perched on your bike seat, then you aren't effectively stabilized to make full use of your pedal stroke. 

Think about this: 
If you have a seat slid all the way back on the rails, so that the seatpost clamp is at the front of the seat, and it is level.  What happens when you sit on the saddle?  What if the rails are made of Steel?  Titanium?  What I'm getting at, is that a saddle has a static (or unweighted) position and a dynamic (weighted) position.  The dynamic position is the only one that really matters.  It has been my experience that especially with titanium railed seats if the seatpost clamp is to the back of the rails the seat will flex downward, if towards the front of the rails the seat will flex backward.  Therefore I have allowed some seats to leave my Studio tilted up or down at times to accommodate.

This leveling of the seat brings me to my last point about a good seat -- for a man or a woman.  The seat should have at least some portion of it's surface should be flat and not fully sloping. 

This FSA saddle is a good example of when some seat designs can cause trouble for people.

The centerline of the seat is the high point and the cover slopes downward to either side.  I am sure there are people who find this saddle comfortable, but I haven't met them yet.

I am intrigued by the new fizik Antares -- the entire saddle looks flat.  I will have to try it out and get back to you on that one.

Next up :  Some top secret stuff going on in the lab.  Well, not really secret, but it should be pretty cool.  We are combining the use of the Retul dynamic "mo-cap" with a very sensitive biofeedback system so we can see what exactly some muscles are doing when we pedal, and using all the information (and there is tons!) to try to determine what the leg muscles are doing when....say, a knee tracks laterally more then the other side. 

From the preliminary findings, I think I can say that many will be surprised at what we are finding.


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