Continuous Postural Regulation: The Cone of Balance as a Dynamic Model

Introduction

Postural regulation is a continuous, largely unconscious sensorimotor process that allows the human body to maintain its orientation and balance despite internal disturbances (breathing movements, shifts of body segments) or external ones (changes in support, uneven surfaces). It relies on a three-step loop [1–4]:

• first, perception: proprioception, vision, and the vestibular system;
• next, integration: the information is combined by the central nervous system;
• finally, action: an appropriate muscular and joint response.

Balance, therefore, does not mean the absence of movement. When standing, the body constantly makes small, controlled oscillations of the center of mass and center of pressure — postural sway. These oscillations do not necessarily reflect a lack of stability: they reflect the activity of a system that continuously adjusts the body’s position relative to its base of support [5–8].

This dynamic view thus aligns with the cone of economy proposed by Jean Dubousset: when the body is efficiently organized, standing is maintained with a limited number of corrections and reduced muscular effort [9, 10].

What This Article Covers

This article therefore examines the cone of balance as a dynamic model of postural regulation. In particular, it covers:

• first, Dubousset’s cone of economy, of which the cone of balance is the functional extension;
• next, the role of proprioception in perception;
• ankle, hip, and stepping strategies;
• the application of this framework to natural postures, then to sitting and to the Aporia® architecture.

In addition, each section distinguishes what is established in the literature, what belongs to Blue Portance’s interpretive model (the SBNFA™ framework), and what remains a hypothesis to be evaluated, particularly for Aporia®.

1. Dubousset’s Cone of Economy

The cone of economy was described by Jean Dubousset based on the analysis of standing posture and the global balance of the axial skeleton. It relies in particular on the concept of the chain of balance, which links the feet, ankles, knees, hips, pelvis, spine, and skull [9, 10].

This chain is not a simple stack of segments, because each region influences the others. A change in pelvic orientation can alter lumbar lordosis, which in turn can influence thoracic posture, and then the cervical adjustment needed to keep the gaze horizontal [11, 12].

In an economical organization, the segments position themselves to limit the moments of force and the muscle contractions needed to maintain posture. The body is not motionless, however: it remains animated by micro-movements, but these are contained within a zone compatible with limited energy expenditure. When the organization becomes less favorable, the body can still maintain balance, but at the cost of a wider cone, more compensations, and increased muscle activity [9].

Cone of Economy and Decompensation

For example, in sagittal spinal imbalance, the body tries to keep the head above the pelvis and the gaze horizontal. To do so, it may increase pelvic retroversion, bend the knees, or shift the trunk [11]. These strategies maintain standing for a certain time, but they are not economically neutral: they can increase muscular demand and reduce the margins for adaptation. Moreover, recent work proposes using the enlargement of the cone of economy as an indicator of decompensation in patients with adult spinal deformity [13].

2. From the Cone of Economy to the Cone of Balance

Admittedly, the cone of economy describes an efficient organization. However, dynamic regulation adds another question: how does the body respond when it is moved, disturbed, or faced with a new task? This capacity depends as much on overall alignment as on the availability of motor strategies [5–8].

In this article, the cone of balance refers to the functional space within which the body can move its center of mass, stop, remain stable, then move again, and respond to a disturbance without losing postural control [24]. It does not replace the cone of economy; instead, it extends it by incorporating movements, corrections, and changes in support. It is not an anatomical volume, but a way of connecting Dubousset’s model to the mechanisms of dynamic postural control.

To visualize it, you can picture a volume centered on the base of support, within which the center of mass can move without the person needing to take a step. This representation, however, remains a teaching aid, not a measurement.

3. Center of Mass, Base of Support, and Limits of Stability

In a simplified static situation, balance is favored when the vertical projection of the center of mass stays within the base of support. However, this rule is not enough to describe dynamic situations [8, 14].

Indeed, the center of mass has velocity and acceleration. The body can therefore remain in control even as its projection approaches the edge of the base of support, provided the center of pressure and muscular forces can still alter its trajectory [14, 15]. Finally, when the disturbance exceeds the joints’ capacity for correction, the body can move its base of support by taking a step [16].

Factors That Affect Stability

4. Perception: The Role of Proprioception

Proprioception encompasses information about the position and movement of body segments. It does not directly measure the position of the center of mass: the nervous system therefore combines this information with vision and the vestibular system to estimate the overall state of the body and organize corrections [2, 3].

It relies mainly on three families of receptors [2]:

• first, muscle mechanoreceptors: muscle spindles (length and stretch velocity) and Golgi tendon organs (musculotendinous tension);
• next, joint receptors, sensitive to loads on the joint capsules and to movement;
• finally, skin receptors, particularly those on the soles of the feet, which report pressure and displacement relative to the support surface.

Indeed, this information is not used separately. Thus, if one source becomes less reliable, the weight given to the others can be adjusted [3, 4]. Proprioception therefore makes it possible to detect disturbances, to anticipate postural needs (for example, before raising an arm, the trunk muscles contract to stabilize the pelvis), and to adapt the response to the nature of the support.

Proprioception and Fascial Tissue

Fascial and connective tissues contain nerve endings and mechanosensitive structures; several studies have therefore suggested that they may contribute information about tissue tension, deformation, and movement [20, 21]. However, this contribution should not be isolated from that of muscles, joints, and skin.

5. Regulation Strategies: Ankle, Hip, and Stepping

The postural control literature traditionally distinguishes the ankle strategy, the hip strategy, and the stepping strategy. They are presented separately to simplify the analysis, but they combine and overlap in real-life situations [17–19].

The Ankle Strategy

It is generally used for small disturbances on a firm, sufficiently wide surface: the body behaves roughly like an inverted pendulum pivoting around the ankles, and the leg muscles modulate the forces exerted on the support to shift the center of pressure [17, 18]. By contrast, it becomes less sufficient when the support is narrow or moving, or when the disturbance is fast and large.

The Hip Strategy

It comes into play more when the disturbance is large or fast, or when the base of support is reduced or less stable. It then engages the pelvis, hips, and trunk to rapidly change the position of the center of mass [18]. It is not a “superior” strategy: for example, an excessive hip strategy in a situation the ankles could control can increase trunk sway.

The Stepping Strategy

When joint corrections are no longer enough, the body can move its base of support by taking a step [16]. Yet it is not only a last resort: a step can also be anticipated or voluntary when moving is part of the task.

The Role of the Pelvis

The pelvis is the mechanical interface between the lower limbs and the trunk: its movements change trunk orientation, load distribution, and the trajectory of the center of mass. It is thus particularly involved in the hip strategy.

6. Natural Postures and the Cone of Balance

The SBNFA™ framework defines a natural posture as a body configuration in which the body retains a capacity for adjustment, load redistribution, and active regulation. It therefore cannot be reduced to a stable geometric shape [24].

The Example of the Hadza of Tanzania

For example, the study of the Hadza of Tanzania illustrates the difference between rest and immobility: adults spend a notable share of their non-ambulatory rest time squatting, a posture in which muscle activity remains higher than that observed in a chair [23].

Comparing Postures

These postures can then be analyzed according to their influence on the height of the center of mass, the base of support, and the availability of motor strategies. Squatting brings the center of mass closer to the ground and can increase mechanical stability in some configurations, but it requires sufficient mobility of the ankles, knees, and hips. In addition, kneeling changes the base of support and the distribution of pressure, at the cost of possible stress on the knees. Finally, sitting on the floor allows several configurations and transitions, without suiting every body type.

Neither Good nor Bad by Nature

7. How Aporia® Makes Postural Regulation Possible While Sitting

When sitting, the base of support changes: the feet are no longer the only support, the ankles do not play the same role as when standing, and the seat becomes a mechanical partner of the pelvis. The question, therefore, is not how to transpose standing strategies as they are, but what the seat allows the pelvis and hips to do.

Thus, on a conventional seat, support on a fixed, single-piece surface limits the relative mobility of the hips and pelvis, reduces compensatory adjustments, and keeps loads on the same areas [26].

The SBNFA™ framework therefore frames this question through its postural balance regulation function. Balancing relies on the coordinated — yet functionally independent — action of the right and left hip–ankle chains. A seat preserves it when it allows the person to move in several directions, to stop at different points within their range of freedom, to remain stable there, and then to move again, without being systematically pulled back to an imposed zero point [24].

It also sets a precise limit on what a seat can do: proprioception is not “produced” by the seat. The question is how the seat handles the mechanical information the body gives it (pressures, tilts, micro-movements): it can block it, absorb it, process it globally, or respond to it locally, in a differentiated and proportionate way [24].

The Aporia® Architecture

The Aporia® ExoBase thus combines a curved, mobile base with four articulated, mechanically independent pads (front right, front left, rear right, rear left), each with its own foam and its own cover. When the pelvis shifts to one side, the right and left zones can respond separately, and the pads preserve the local origin of the loads [25]. The framework thus describes a continuous space of balanced oscillations up to ±50°, within which the person can move from one stabilized position to another without having to maintain an imbalance imposed by the seat [26].

What the Evaluation Allows Us to Say

However, this evaluation is expert-based, not instrumented: it covers the capacities offered by the architecture, not how a given person uses them, and it concerns a prototype that is not yet commercially available [25, 26]. The framework also documents limitations: horizontal displacements and spine–pelvis pivoting are bounded by the geometry of the assembly, pressure distribution depends on body type and adjustment, and firmness cannot be adjusted separately on each pad [25].

8. Conclusion

In summary, Dubousset’s cone of economy is a major model of global balance. The cone of balance is its functional extension: it describes the body’s capacity to move its center of mass, stop, remain stable, and then move again [9, 24].

Moreover, postural regulation adds a dynamic dimension to economical organization: perception, integration, and action form a continuous loop, and ankle, hip, and stepping strategies allow balance to be maintained or recovered depending on the size of the disturbance [1–4, 17–19].

Applied to sitting, this framework therefore leads to one criterion: not “does the seat move?” but “what does it allow the pelvis and hips to engage, differentiate, stabilize, and adapt?” The Aporia® architecture is designed to meet this criterion; however, its effects on proprioception, hip coordination, mechanotransduction, and pain remain to be objectively evaluated.