This blog is attracting more hits than I ever thought likely. So far the U.S is no. 1. A population of 300 miilion means a lot of bike riders, Then close behind is Australia, then the U.K. No surprises there. Then before strong cycling countries like Italy, France, Germany, Spain and Belgium, is Romania contending for fourth place with Canada. I don’t know a great deal about Romanian cycling but it seems they have a lot of keen cyclists hitting the net. This post grew out of the enquiry below in the Comments section from Mircea, one of our Romanian readers. It is worth reading because Mircea has a brain and uses it to make some insightful comments, particularly regarding relative pelvic shapes / proportions. While reading, please keep in mind that English is not Mircea’s first language, though he does a good job of getting the message across.
i don’t know the best title for what i want to write, maybe Pelvis-Placement into the body riding locomotion, something like that. i’ll write here, and after you can place it wherever fits better. thanks!
Everybody’s speaking about sitting on seat bones, but looking at the pro riding i see that almost all of them, most of the time, they sit on the perineum . And for TimeTrial looks like all of them sit on the perineum. This is what i see and i do not understand. Also for myself, when i ride my bike, i feel like if i want to push harder then i had to sit on the perineum. I asked once a woman pro rider about that and she reply “no, we all sit on our seat bones”. I am not convinced, my eyes tell me something else. I am so confused!…
For me it looks like you can stay three ways on the saddle:
1) only on the seat bones. maybe slightly touching with your perineum and pubic bone;
2) on the seat bones and the perineum / pubic bone, like a 3 point platform;
3) only on the perineum /pubic bone.
When we stand vertical on our legs, in a biped position, our pelvis has the seat bones a little down from the pubic bone. Some more, some less. From outside, just from aesthetic point of view, i think most people like when the seat bones are placed high (but this is something else). But now, here, i want to talk only about locomotion, physical, practical point of view. So looking from profile/side, we can draw a virtual line between seat bones and pubic bone (it is more like an arch). This virtual line would raise in front of the pelvis and would droop in the back of it. So this line will not be perpendicular with the vertical, but at an angle. Now, sitting on a saddle, because we want our pelvis to sit on our seat bones (maybe slightly touching the perineum/pubic bone) and to tilt forward, this virtual line would be very close to horizontal. If we tilt the pelvis more then we will touch hardly our perineum (pubic bone). My ideea is that the more your seat bones are lower on your pelvis, the more your pelvis will be tilted forward (assuming we sit mostly on our seat bones). I think this is an advantage because you can work better your glutes. People who have high seat bones on their pelvis must sit on their perineum (pubic bone) for having the same pelvis tilt (angle). Otherwise said, one with lower seat bones will have a flatter lower back when sitting on a saddle, but one with high seat bone will have a curved lower back (which leads to some pain, i think); so, for having the same flatter shape the one with high seat bones will, again, tilt more but he will sit mostly on the perineum (pubic bone). These are my opinions from what i see around and what i feel.
I would like to know what do you think about this placement of the pelvis, about this relation/transition between seat bones and pubic bone? I hope you understand my english (it’s not my language), the terms i used 🙂
Also, what should happened when you move your hands form brake hoods to drops on a road bar? Does your pelvis move/tilt a little bit, or it should stay in the same position and only the spine would arch more?
I like a lot Fabian Cancellara. For me it looks like, compared to the others, he use more his glutes. He is very stable on his bike, his lower back looks quite flat (very little arch), and his legs (knees) realy look like pistons. I think this has to do with his pelvis being more tilted compared to the others. But to perform with this pelvis tilt, you should be realy flexible in the hip joint and in the hamstring muscle, which i heard that Cancellara is. He use quite a lot of saddle setback, now on his bike he has: 73° seat angle, 20mm offset seat post, and his saddle maximum back. Now, if this is the case, how to achieve this pelvis tilt but still being comfortable?… i do not know.
Good observation and equally good questions Mircea. I’ll tackle your questions one at a time. Firstly, I need define a few terms that you’ve used for other readers. If viewing the pic above:
The Sit Bones or as you have called them, Seat Bones (properly called the Ischial Tuberosities) are the bulbous, bony projections immediately above the right hand side of the M and over the P of Selle SMP embroidered logo on the seat. This is where the hamstring muscle group originates.
The Pubic Bone (which you have incorrecly conflated with Perineum) is the bony projection immediately above the ‘a’ in Dynamic on the side of the seat above.
The Ischiopubic ramus is the bone connecting the Ischial Tuberosity and the Pubic Bone on each side.
The Perineum is the area of soft tissue (and structures underneath it) between the anus and the genitalia.
Now to answer your questions which I have cut and pasted in bold text.
Q. I would like to know what you think about this placement of the pelvis, about this relation / transition between seat bones and pubic bone? I hope you understand my English (it’s not my language), the terms I used.
A. Mircea, I understand you well. Your English is fine. Certainly far better than my Romanian! Re what you’ve said above. You may well be right. While all humans have the same basic pelvic anatomy, there is wide variance in proportions and shape. What you are saying is that the profile as viewed from the side of the ischiopubic ramus (the part of the pelvis linking the sitbones and the pubic bone which contact the seat in the pic above) can vary markedly in shape. In some people it dips lower and is more rounded and in others it is flatter. You are correct but I cannot tell you in detail how that affects the way different riders sit on a bike for 2 reasons. One, I don’t examine that area of my fit clients and I’m sure that you can understand why. Secondly, it is only one part of the functional make up of a human being. Yes, it has an influence on how comfortably a particular rider can lean forward to the bars, but so does the shape and range of motion of the sacro iliac joints and the flexibility of the muscles that affect the hip and low back as well as the riders ability to extend their spine and neck..
Given that I don’t know in detail what the pelvic anatomy of any client is, I work with what I can see and test and try to ensure that a fit client leaves with a seat that they are comfortable and securely seated on. Sometimes this is a matter of trial and error. These differences in shape, function and abilities (and the position that they currently hold) explain the phenomenon we are all familiar with where a rider will think a particular seat is the most comfortable device ever mounted on a bike while another will think it an instrument of torture. Still others will have a spectrum of opinions within that range . Positional parameters play a part in this too, a large part, but I think the basic answer to your question is that there are large variances in human anatomy that for obvious reasons cannot be known beyond a certain level of detail with any fit client, and so trial, error and rider feedback play a part in achieving the ‘right’ seat / human combination in any particular case. At least until I get my X ray vision working or fit clients allow me to be much ‘friendlier’.
As an aside, see the pic above. The sacro iliac joints (SIJ’s) are the joints immediately in towards the centre line from the pins located half way up the pelvis. A good range of movement of the SIJ’s allows a rider to point their ‘tail’ and have a lower torso than if they have a poor range of movement in these joints. There is large individual variation in SIJ mobility and this too plays an important part in how the rider contacts the seat.
Q. Also, what should happen when you move your hands from brake hoods to drops on a road bar? Does your pelvis move /tilt a little bit, or should it stay in the same position and only the spine would arch more?
A. There are too many variables to give you a yes / no type answer. Some of the variables are –
- The physical relationship of the brake hoods to the drops can vary markedly depending on at what height the brake hoods are positioned on the bar
- Some brake hoods are far longer than others. Sram for instance are shorter than Shimano. Campag are different again.
- Bar drop can vary as much as 40+ mm on road bars
- Bar reach can vary from around 65mm to around 100mm on road bars.
- Above all, the position the rider currently holds, how functional / flexible they are and how they achieve that flexibility is a variable.
- The profile of the long axis of the seat will play a part.
My feeling is that the rider should be able to exercise all of their hand placement options comfortably. A recreational rider may spend hardly any time in the drop bars but they should be positioned in such a way as to allow them to do it without discomfort for a reasonable time frame if they choose to do so. What changes an individual rider will make in body position to reach from brake hoods to drops will be like everything else that happens on a bike……… individually variable. The aim is always to allow the rider to be ‘themselves’ in as stable, comfortable and powerful way as possible. For some this will mean a movement in forward tilt of the pelvis; for some it will mean spinal flexion increases (which is okay providing it doesn’t cause potential for problems, which if they occur, usually affect the neck first) and for some it will be a combination of both. If you are asking as to which is ideal; in a rider with good function, I think the majority of change should occur with a combination of forward tilt of the pelvis and and sacro iliac joint movement allowing a flatter back.
Q. I like a lot Fabian Cancellara. for me it looks like, compared to the others, he uses more his glutes. He is very stable on his bike, his lower back looks quite flat (very little arch) and his legs (knees) really look like pistons. I think this has to do with his pelvis being more tilted than the others. but to perform with this pelvis tilt, you should be really flexible in the hip joint and hamstring muscle, which I heard that Cancellara is. He uses quite a lot of saddle set back, now on his bike he has: 73 degree seat tube angle, 20mm offset seat post and his saddle maximum back. Now, if this is the case, how to achieve this pelvis tilt but still being comfortable?…………. I do not know.
A. Firsty it is an assumption that he is comfortable but without knowing him, I think he is because he smiles a lot. So for the purposes of discussion, we’ll take his comfort as a given. Okay, a 73 degree seat tube angle (STA) with seat jammed all the way back yields an ‘effective’ STA of 72 degrees, give or take, depending on seat choice. That is not strange or unusual and human variance and function dictate that a much wider range than that is needed to allow the cycling portion of humanity to ride a bike comfortably and powerfully. I’ll call 73 degrees a midpoint, which in my experience it pretty much is. The further you move in either direction from 73 degrees, the lesser the percentage of people who need a particular STA. 72 degrees is not ‘unusual’.
Having seen Cancellara on TV numerous times, I agree with you. His position is low and long and the way that many people think they would like to look like on a bike. I don’t know what seat he rides but unless it is an SMP or other brand with large perineal cut out, there will be contact between Cancellara’s perineum and the seat. Contact and uncomfortable pressure are two different things and from the outside looking in, some combination of function, pelvic shape and proportions and seat shape allow him to do as he does. The gist of what I’m saying is that all of your points are good ones but we are not workng with full knowledge, even of ourselves, when we ride a bike. Unless we have had extensive imaging procedures, none of us knows what the detail of our own, or our fit client’s pelvic shape is, or how it differs from the hypothetical norm (assuming that there is a norm). So we are left with the tools that all of us have; the ability to feel pressure and the ability to individually decide on what is acceptable in the pressure continuum that has Ideal Comfort at one end of the scale and Agony at the other end..
The pic below is illustrative as it shows the front view of the other two photos. It is not just sit bone pressure felt on a seat. One of the reasons I am a fan of the SMP range is that most people sit on a seat and feel diffuse pressure with a localised increase at the sit bones, or less ideally, the perineum. When you sit on an SMP seat, you will feel sitbones and the entire ischiopubic ramus without the perineal pressure that can accompany this for many people. SMP have simply removed the middle of the seat. They have wide range of seats with differing profiles as viewed from side, with differing padding thickness and different seat widths. While there is no seat that suits everyone, the great majority of people can achieve ideal comfort on the individually ideal model from the SMP range (assuming the seat is well positioned for them) because it removes the potential for perineal pressure that concerns you from the riding equation.
What I try to do when fitting an SMP is by trial and error, find width and profile that best matches the curve of the base of that rider’s pelvis. I doubt my customers are interested in me making an intimate examination of them, so this is way that it has to be.
While on the subject of seats, a story from the past. Years ago when trying to determine which seat was best suited to a rider, I used to get the rider to sit on a flat wooden chair that I had sprinkled with talcum powder. They would carefully sit, contact the chair and then stand again. The pressure of their sit bones would be obvious in the talcum powder and I would then measure the separation of the sit bones and try and match that to an appropriate seat width. What I found was that there was a correlation of sorts between pelvic separation width and seat width around 75% of the time only. With the remainder, people with wide separation were more comfortable on seats narrower than I would have expected and people with smaller separation were more comfortable on wider seats than I would have expected.
I always assumed and still do, that the seeming anomaly of 25% who chose seats not obviously of the ‘right’ width was caused by having a curve of the ischiopubic ramus that allowed them to sit comfortably on seats that ‘seemed’ not to suit them. So trial and error is still the best way. Additionally, the ischiopubic ramen narrow from rear to front so the further forward the rider can roll their pelvis, the narrower the separation width between the ramen.
I know I have not given you the definitive answers that I suspect you wished for, but this has been the best I can do.
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