Calcaneal – Ischial Phase Parallel
A Structural and Functional Bridge Between Walking and Sitting
Posted on: April 29, 2026
Author: Dr. Scott W. Donkin, DC, DACBOH
For more than four decades, my work has centered on a deceptively simple question:
Can sitting be solved?
That question began in the early 1980s with clinical observations of patients whose symptoms were influenced not only by injury, but by the way they sat throughout their day. Over time, patterns emerged – patterns that led to the development of Sitting on the Job, decades of clinical practice, and ultimately the framework now known as Power SittingTM.
Along the way, certain recognitions stood out. One of the most important was the structural and functional similarity between the ischial complex – the primary weight-bearing structure in sitting – and the calcaneus, or heel bone, in standing and walking.
More recently, another pattern has emerged. This one extends beyond structure. It suggests a deeper connection between how we sit and how we walk.
I refer to this recognition as the Calcaneal-Ischial Phase Parallel.
The Recognition
When observing X-ray images of the calcaneus during walking, one particular image stood out: the moment of heel strike.
At heel strike, the broader, flatter, posterior portion of the calcaneus contacts the ground. This is the initial point of load acceptance. It is stable, but not yet fully organized for efficient load transmission through the rest of the body.
At first, this image seemed unrelated to what I was studying. But the visual stayed with me.
Later, it became clear why.
That same relationship – broad posterior contact with incomplete structural organization – is strikingly similar to what occurs at the ischial tuberosities during slumping.
In both cases, the body is in contact with a support surface, but the load is not yet optimally organized.
From that moment, the rest of the pattern came into view.
A Parallel Between Walking and Sitting
The calcaneus moves through a sequence during walking:
- Initial contact (heel strike)
- Transitional loading
- Organized stance support
These are not just moments in time. They represent changing relationships between anatomy and load.
Now consider the Sitting Spectrum:
- Slumping
- Upright sitting
- Power SittingTM
What becomes apparent is a meaningful correspondence:
- Heel Strike ↔ Slumping
Load is accepted, but primarily through a posterior, less organized contact surface. - Transitional Loading ↔ Upright Sitting
The body begins to organize, but the relationship between structure and support remains incomplete. - Organized Stance ↔ Power SittingTM
The structure aligns for efficient load transfer, and the body above organizes with minimal compensatory effort.
This is not merely a visual analogy. It appears to reflect a shared functional logic.
The Role of the Ischial Complex
In sitting, the ischial tuberosities and the inferior ischiopubic rami form what I refer to as the ischial complex.
This structure is often treated passively – as something we simply “sit on.”
But when viewed through the lens of weight-bearing function, it behaves much more like the calcaneus:
- It accepts load
- It transmits force
- It influences alignment throughout the body
In slumping, load is concentrated posteriorly on the ischial tuberosities.
In Power SittingTM, the orientation of the pelvis changes. The ischial complex assumes a more vertically organized relationship to the support surface, allowing load to distribute more effectively – similar to how the calcaneus functions in an organized stance phase.
A Deeper Implication
This recognition suggests that sitting may not be a static or passive condition.
Instead, it may be understood as a spectrum of load-bearing relationships, similar in principle to the phases of walking.
This has important implications.
Walking is universally recognized as natural, functional, and essential.
Sitting, by contrast, is often treated as inherently harmful or something to be minimized.
But if the primary weight-bearing structures in sitting move through relationships that parallel those of walking, then sitting itself is not the problem.
Unskilled sitting is.
Power SittingTM in Context
Power SittingTM represents the most complete and organized phase of the Sitting Spectrum.
It is not simply “good posture,” nor is it a forced or rigid position.
It is the result of aligning the pelvis – and therefore the ischial complex – in a way that allows the body to organize itself efficiently.
When this occurs, a recognizable pattern often follows:
- The shoulders align over the hips
- The shoulder blades approximate naturally
- The head moves into balanced alignment
- The body feels supported rather than held
This is not imposed. It emerges.
Seen through the Calcaneal–Ischial Phase Parallel, Power SittingTM can be understood as the seated counterpart of an organized stance phase in walking.
Evolutionary Ergonomics
This concept also contributes to a broader framework I describe as Evolutionary Ergonomics.
If human anatomy reflects design shaped through interaction with gravity and movement, then how we sit should not be disconnected from how we stand and walk.
The body does not abandon its design principles when we sit.
Instead, those principles may still be present – waiting to be recognized and applied.
The Calcaneal-Ischial Phase Parallel offers one way of seeing that continuity.
A Continuing Inquiry
This recognition represents an early articulation of an emerging pattern.
It is based on clinical observation, anatomical comparison, and visual analysis, and it will continue to be refined through further study and application.
What is clear at this stage is that:
- Sitting is not a singular behavior
- It has distinct phases
- Those phases appear to reflect deeper structural relationships
- And those relationships may connect sitting to more fundamental human functions such as walking
If so, the implications extend beyond posture.
They reach into how we understand human interaction with support, load, and organization itself.
Authorship Note
The concepts presented here are part of the ongoing development of Power SittingTM and related frameworks, including Evolutionary Ergonomics, based on continuous clinical practice, teaching, and pattern recognition beginning in the early 1980s and continuing through the present.
©2026 Scott W. Donkin. All rights reserved.