Seat Bones vs. Pubic Arch in Riding

Over the past few weeks, my posts about pelvic position in the saddle have generated some of the liveliest discussions I’ve seen on my social media accounts. That is a brilliant thing, because debate forces us to reflect, to ask questions, and to make better-informed decisions as riders. But what has become very clear is that there are strong and opposing views on how the pelvis should be positioned in the saddle. But without reasoning and rationale how is a rider to make an informed decision on what is or is not correct?

The diagram on the left was a screenshot someone sent me of what a neutral pelvic should look like in the saddle from a well known riding coach. Versus what is considered a neutral pelvis in the medical world (thanks to www.posturegeek.com for the diagram)

This might feel like an essay more than a blog sorry! But I think it is important if you have an opinion about something you should be able to reason your thought process with research and rationale not just personal experience.

One post of mine in particular, where I explained that the ischial tuberosities (the seat bones) are designed as the primary weight-bearing structures in sitting, caused a lot of controversy. One person asked who designed them that way - was it God, or Darwin’s theory of evolution?

My own view is that it comes down to bony remodelling over time, in keeping with what we know from anthropological and bipedal studies. As humans evolved to walk upright, the pelvis broadened, the sacrum reoriented, and the ischial tuberosities enlarged to provide stable support in sitting. Regardless of one’s personal beliefs, the outcome is the same: in modern human anatomy, the ischial tuberosities are the structures adapted to bear weight in seated postures.

And yet, in equestrian discussions, I repeatedly hear the same refrains: that riders should have weight through the pubic arch, that a “neutral pelvis” is not really neutral, that the seat bones are not the correct structures to sit on, and even that once a rider has “found the seat bones” they should “lift them” so that the rider carries himself and the horse carries himself. These are memorable coaching cues, and they no doubt help some riders in certain contexts, but when we analyse them against anatomy and biomechanics they do not hold up (do you levitate out of the saddle to carry your own weight?!)

The anatomy of the pelvis

The human pelvis is not a single lump of bone but a ring made of three parts: the ilium, the ischium, and the pubis. Each part has evolved to serve different functions. The ilium provides wide, flaring blades that protect abdominal organs and serve as strong muscle attachment sites. The ischium forms the ischial tuberosities, bony prominences that are reinforced and cushioned by soft tissue - the structures specifically adapted to carry weight in sitting. The pubis forms the pubic arch and the pubic symphysis, a fibrocartilaginous joint whose role is to provide stability and protect the bladder, reproductive organs, and pelvic floor. Unlike the ischial tuberosities, the pubic arch is not designed for sustained load. You can of course put weight through most bones in the body- it doesn't mean you should though.

This is not a matter of opinion. It is described consistently in standard anatomical texts such as Gray’s Anatomy and confirmed in ergonomic and rehabilitation research. The ischial tuberosities are repeatedly identified as the main weight-bearing prominences in sitting; the pubic arch is not.

What other bipeds tell us

Looking beyond humans to other bipedal mammals strengthens this point. Apes and monkeys also have ischial tuberosities, but in their case they are covered by thickened pads known as ischial callosities, which allow them to perch on branches. Theirs are more posteriorly oriented, adapted for a mixture of quadrupedal locomotion and occasional perching. Humans, by contrast, evolved broad, downward-facing ischial tuberosities remodelled specifically for upright sitting, with muscular and fatty padding that disperses pressure.

Kangaroos, another group of bipeds, do not sit on their pubic arches either. When they rest, they use their tail as a third support, forming a tripod with their hindlimbs. The tail takes the load, not the pubic region. Birds, though obligate bipeds, have completely different pelvic anatomy, with fused bones and perching mechanisms that bear weight through entirely different structures.

In short: where bipedal mammals do sit, they sit on their ischial tuberosities or equivalent. Nowhere in comparative anatomy do we see the pubic arch being used as a load-bearing surface. Its function remains protection and stability.

What neutral really is - and why it can’t be defined by contact with the pubic arch

There is a lot of confusion in the equestrian world about what a “neutral pelvis” actually is. I often hear riders or trainers describe neutral as the position where the pubic bone is also in contact with the saddle. I disagree with that definition, because it ignores both anatomy and biomechanics.

First, saddle design itself changes how much contact the pubic arch has. A deep-seated saddle with a high cantle will position the pelvis differently than a flatter saddle. If “neutral” depends on whether the pubic bone touches the saddle, then neutral suddenly becomes a moving target, defined not by the rider’s anatomy but by saddle shape. That makes no sense.

Second, and more importantly, neutral cannot be defined by pressing weight into a structure that was not designed to bear weight. The pubic symphysis is a fibrocartilaginous joint that protects the bladder, reproductive organs, and pelvic floor. It does not have the padding or bony architecture to act as a stable load-bearing surface. If a rider tips forward to “include” the pubic arch, they are already moving away from neutral, not into it.

For me, neutral must be defined relative to the seat bones. When the pelvis is balanced on them, the spine maintains its natural curves, and the hips are free to move. This creates the conditions for isolated movement at the hip and the spine, which is essential for following the horse without gripping or collapsing.

If the pelvis tilts anteriorly, the seat bones roll backward and upward, lifting partially away from the base of support. This unloads them and increases pressure onto the pubic arch and perineum (soft tissue between the pubic symphysis at the front and the coccyx at the back containing muscles, fascia, nerves, and blood vessels that form the pelvic floor and support the bladder, bowel, and reproductive organs). Because the perineum is made up of delicate soft tissue rather than bone, it is not designed to bear sustained pressure

When the pelvis tilts forward, the acetabulum rotates downward, bringing the femoral head into a more flexed position relative to the trunk and effectively closing the hip angle. This reduces available hip range and forces the lumbar spine to over-extend in compensation to keep the rider upright. That’s when we see hollow backs, tension, and bouncing seats. Muscles have to work to keep body upright in a different way. The joints then become loaded in a different position (extended) to what is optimal and can lead to injury.

If the pelvis tilts posteriorly, the seat bones roll and the sacrum becomes the main contact point. The pelvis stiffens, hip motion is restricted, and the rider tends to lose the dynamic swing needed to follow the horse.

Neutral, therefore, is the point where the ischial tuberosities bear weight symmetrically, the pubic arch is protected (not loaded), and the pelvis can move freely in all directions. That definition does not depend on saddle design, on coaching metaphors, or on “contact points.” It is grounded in how the pelvis is built to function. And this will look different on every rider.

If you’re not on your seat bones, you’re either collapsed back on your sacrum or tipped forward onto your pubic arch/perineum. Both are mechanically less stable and not recommended.

What neutral spine really means

Some define a neutral spine as being “neither flexed nor extended,” but this oversimplifies the reality of spinal curves. If the spine were completely vertical and straight, with no flexion or extension at all, it would be structurally weaker and less efficient at absorbing forces. Just as a wavy brick wall is stronger than a straight brick wall, the spine is stronger and more resilient because of its natural curves.

In true neutral, the lumbar spine maintains a small lordosis (a gentle extension curve), the thoracic spine maintains a small kyphosis (a gentle flexion curve), and the cervical spine again has a mild lordosis. These alternating curves distribute load, allow shock absorption, and enable smooth mobility.

So for me, neutral is not “flat” or “straight.” Neutral is the natural alignment where these curves exist in balance, and where the pelvis sits so that the ischial tuberosities are the main weight-bearing base. From this position, the hips and spine can move independently, and the rider can follow the horse with minimal bracing or collapse. And why no two riders will look the exact same.

Standing vs. sitting: changes in lumbar lordosis

It is also worth remembering that spinal alignment is not fixed - it changes with posture. In standing, the lumbar spine naturally has a lordotic curve, supported by the pelvis being in a relatively neutral to slight anterior tilt. But when we sit, research shows that lumbar lordosis typically decreases. The pelvis rotates posteriorly, flattening the lumbar curve (Claus et al., 2009; Bridger, 1988).

This means that “neutral” when sitting is not identical to “neutral” when standing. Neutral in the saddle is the point where the pelvis is balanced over the ischial tuberosities and the lumbar spine holds a gentle, functional curve that allows mobility without collapse - not the exaggerated extension of standing lordosis, and not the flattened curve of slumped sitting. Recognising this distinction is critical, because it helps us avoid chasing an impossible ideal of “standing posture” in the saddle, and instead focus on functional balance and movement.

What rider biomechanics research shows

Direct research into riders, while limited, points in the same direction. Münz et al. (2014,) found that elite riders maintained a neutral or slightly posterior pelvic tilt, centred over their ITs, which allowed the pelvis to move dynamically with the horse’s movement. Engell & Byström (2016) similarly showed that skilled riders remained balanced over the seat bones, whereas novice riders tipped forward. Byström et al. (2010) observed that novices rolled into anterior tilt, partially loading the pubic arch, and that this was associated with increased thigh tension, gripping, and instability.

The pattern is remarkably consistent.

Skilled riders = neutral/posterior tilt, weight through ischial tuberosities.

Novices = anterior tilt, weight partly through the pubic arch, resulting in instability.

Evidence from sitting and ergonomics

Because riding studies are relatively few, we can also learn from sitting research. Drummond et al. (1982) measured pressure distribution and found that roughly 18% of body weight is borne by each  ischial tuberosity, around 21% along the thighs, and about 5% through the sacrum, with the remainder supported by the feet. This shows that the ischial tuberosities are the natural base of support, but in chairs they share some of the load with the thighs and feet.

Makhsous et al. (2009) demonstrated what happens when the ischial tuberosities are offloaded: pressure shifts forward into soft tissues, and lumbar muscle activity increases as the trunk works harder to remain upright. Stinson (2002) and Gilsdorf (1991) showed that  ischial tuberosities remain the main weight-bearing base until about 10° of posterior tilt. Even then, the load does not vanish - it simply shifts to areas less suited to handle it, such as the sacrum.

In a saddle, these dynamics are amplified. Unlike in a chair, the thighs no longer rest flat, and the feet do not provide the same stable base. The thighs drape down in abduction, narrowing the base of support, so the pelvis must carry more of the rider’s weight. Far from reducing the importance of the ischial tuberosities, this increases it. But now the legs are under the pelvis and so under the base of support (or widening it)- a whole other blog about why legs do and don't affect pelvic position in the saddle!

The role of stirrups and foot support

Foot support makes a major difference to pelvic loading. Koshi et al. (2010) and Sprigle & Sonenblum (2011) showed that when feet are unsupported, pelvic load rises and ischial tuberosities pressure increases by 15–25%. Studies on chair height, dating back to the 1960s and confirmed by Kerr & Ferguson-Pell (1985), demonstrated that lower seats allow more weight to be borne through the feet, while higher seats force more load into the pelvis.

This maps neatly onto stirrup length.

Short stirrups, like a low chair, allow more weight into the feet. Long stirrups, like a high chair, reduce foot support and increase pelvic load. No stirrups, like no foot support, leave the pelvis to bear almost all of the weight.

That is why I sometimes shorten stirrups for riders who do not yet have the strength, mobility, or control to maintain neutral. It gives them more support until they can develop the control for longer stirrups. Forcing stirrups longer or taking them away prematurely often causes anterior tilt, unloading the ITs and collapsing onto the pubic arch.

Stool vs. chair vs. kneeling chair

Studies of different seating types show further evidence of how pelvic tilt changes with support. Sitting on a stool encourages anterior tilt and increased lumbar lordosis because there is no backrest to allow posterior roll. If the thighs are behind the pelvis (as on a stool), the trunk shifts forward for balance. But if the thighs are under the pelvis (as in a saddle), the spine stays more central. Without back support, some people also posteriorly tilt to reduce muscle effort, highlighting how the absence of support changes mechanics.

Kneeling chairs (Bennett, 1979; Mandal; Iwamoto, 2024) create anterior tilt and upright trunk posture, but only because the shins and knees take part of the load. That mechanism doesn’t exist in the saddle, so anterior tilt there simply means offloading the ITs into the pubic arch- without any of the stabilising benefit.

Lessons from cycling

Cycling provides another parallel. It is also seated, also on a narrow base, and also involves sustained load without thigh support. Bressel & Larson (2003) found that reducing IT support increased perineal pressure. Marceau et al. (2010) showed that competitive female cyclists had reduced genital sensation compared to runners, caused by increased perineal loading. Schoberth (1999) found that hip angle did not significantly alter ischial tuberosities pressure between 60–90° flexion; instead, pelvic tilt and saddle design dictated perineal pressure. Lin et al. (2023) confirmed that wider saddles that better supported the ischial tuberosities reduced perineal pressure.

The parallels are obvious: unloading the ischial tuberosities and tipping onto the pubic arch increases pressure on vulnerable tissues, with discomfort and even neurological consequences.

The new trend: saddles supporting the three points

Recently, some saddle fitters and trainers have promoted fitting saddles to deliberately support the pubic arch. They claim it increases stability and is supported by “lots of research.” The difficulty is that none of this research is openly available. It is accessible only through paid training programmes, accompanied by the promise that it will “open your mind” and challenge your beliefs. And it very well might do- but for research to be counted in the scientific communitry it must be transparent.

If the studies exist, where are the inclusion and exclusion criteria? Were novice and elite riders compared? Were pressure-mapping systems validated? Were null hypotheses tested and results shown to be statistically significant? Without this information, the claims cannot be treated as scientific evidence. Have

Have they just identified patterns? Maybe. But does that change with what you want to find? I don't know, but I do know without the papers being available to everyone no one will know unless they pay to do a course.

If, in the future, peer-reviewed research is published showing that supporting the pubic arch improves rider stability without adverse effects, I will read it carefully and be prepared to change my mind. That is how science works. But until then, I will go by the knowledge we already have - the anatomy, the biomechanics, and the research across ergonomics, cycling, wheelchair studies, and riding - all of which consistently point to the same conclusion: that the ischial tuberosities are the natural base of support in sitting, and that loading the pubic arch is unstable and potentially harmful.

Conclusion

The ischial tuberosities have been adapted to bear weight in sitting. The pubic arch is thin, protective, and not designed for sustained loading. Every domain of research, from anthropology and comparative anatomy to ergonomics, wheelchair studies, cycling, and riding biomechanics, points to the same pattern: skilled riders balance over their  ischial tuberosities in neutral or slight posterior tilt, while novices tip forward, load the pubic arch, and destabilise themselves.

Encouraging riders to load the pubic arch contradicts what we know of human anatomy and evolution. No bipedal mammal uses the pubic arch as a weight-bearing structure. When other fields have had to redesign saddles and chairs to prevent perineal loading because of the pain and dysfunction it causes, why would equestrianism promote it as correct?

Until transparent, peer-reviewed evidence shows otherwise, the seat bones remain the stable and sustainable foundation for riding. Because if you are not on your seat bones, you are on your perineum. And that is not a base any rider should want to rely on - discomfort, numbness, and even nerve or vascular compromise is something we should be actively avoiding.

References

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