Biomechanics · functional reading

Functional asymmetry

Functional asymmetry refers to a difference between the right and left sides in the way a person moves, bears load or organizes themselves. It is neither automatically pathological nor automatically useful.

Scientific basis

Asymmetry is common in people without any disorder. In walking, differences between the two limbs, linked to dominance and to different functional roles (propulsion, control), have been described (Sadeghi et al. 2000). Their link with performance or injury risk varies with the task and the measure used (Bishop et al. 2018).

Several levels of asymmetry can be distinguished: anatomical, mobility, load, muscle recruitment, perception, symptoms. An asymmetry can be stable, transient or progressive.

Uneven pelvis: what should be concluded? A pelvis that looks uneven, or a difference between the two sides, does not on its own justify concluding that there is a pathological imbalance, a shorter leg or a need for correction.

Blue Portance / SBNFA™ reading

In the SBNFA™ reading, the hips are the regulator, with right-left independence: a different organization of the two sides is a possibility for adjustment, not a universal rule. A right-left difference may be tolerated, functional, compensatory, context-dependent or clinically significant depending on the task and the person.

Contribution to the analysis of sitting

Seating analysis observes how support is distributed between the two sides and how the pelvis is oriented. A right-left difference is information about the person's organization at a given moment; it is not interpreted as a defect to be corrected.

Not to be confused with

Anatomical asymmetry, limb length discrepancy, scoliosis or morphological difference; Postural compensation, a functional adjustment to a stress; Scoliosis, a deformity of the spine in all three planes; Laterality or dominance, a preference for using one side; Hypertonia, increased tone on one side is only one possible form of asymmetry; "Unbalanced pelvis," "crooked pelvis," everyday expressions, not diagnoses.

Sources and scope

An established biomechanical concept; its clinical significance depends on context. Not every asymmetry is a defect to be corrected, not every asymmetry is adaptive, symmetry is not the norm of health, and a seat does not correct asymmetries. An asymmetry does not on its own explain pain.