Anatomy · functional reading

Fascial stiffness

Fascial stiffness is the resistance of a fascia to deformation; when it increases, the term stiffening is used. The term describes a mechanical property without specifying its cause.

Scientific basis

The stiffness of a fascia is measured in particular by elastography. In humans, it varies with position and muscle activity: the stiffness of the thoracolumbar fascia increases when the knee moves into extension or when the hamstrings contract (Kellis et al., 2024).

Lasting stiffening can have several origins: densification, fibrosis, thickening of the tissue or remodeling of the matrix. In people with chronic low back pain, the lumbar connective tissue appears thicker on ultrasound (Langevin et al., 2009), without it being known whether this is a cause or a consequence.

Stiffness also acts on cells: on a stiffer matrix, fibroblasts activate pathways (YAP/TAZ) that can sustain matrix production (Dupont et al., 2011).

Blue Portance / SBNFA™ reading

SBNFA™ uses "stiffness" and "stiffening" as descriptive terms, not as a diagnosis: it notes that a tissue deforms less, then looks for the mechanism. It distinguishes stiffness from the five alterations described in the Expert Guide, which are possible causes of it. The hypothesis that stiffening reduces a tissue's capacity to redistribute stress belongs to the SBNFA™ reading.

Contribution to the analysis of sitting

Seating analysis does not measure the stiffness of a fascia. It observes whether the position imposes constant deformation on the same tissues or allows the load to shift.

Not to be confused with

Subjective stiffness, a perceived sensation or limitation of mobility; fascial fibrosis, one of the possible causes; muscle hypertonia, an increase in a muscle's tone; fascial viscoelasticity, a normal behavior whose apparent stiffness varies with the rate and duration of loading.

Sources and scope

Stiffness is measurable; its clinical interpretation in a given individual remains limited.