Fascial viscoelasticity

Scientific basis

Human lumbar fascia shows viscoelastic behavior measured directly in tension (Yahia et al., 1993). Four phenomena follow from this: – creep: under a constant load, the tissue continues to deform; – stress relaxation: held at a given length, the tissue requires a decreasing force; – hysteresis: during a loading and unloading cycle, part of the energy is dissipated; – nonlinearity and anisotropy: stiffness increases with elongation and depends on fiber direction.

Creep under sustained load has been measured in the seated lumbar spine (Adams and Dolan, 1995). A tissue's response therefore depends on its history over the preceding minutes, not only on the load of the moment.

Blue Portance / SBNFA™ reading

SBNFA™ draws a direct consequence from viscoelasticity: duration of exposure matters as much as intensity. Mechanically, periods of unloading interrupt creep and allow partial recovery; this is a property of the tissue, not a clinical outcome. The hypothesis that regular variations in support limit the effects of a sustained load is part of the SBNFA™ reading.

Contribution to the analysis of sitting

A prolonged sitting position combines creep, stress relaxation and micro-cycles linked to spontaneous adjustments. The analysis observes how long a position is held and how often support shifts, which contribute to the alternation of loading and recovery in the tissues.

Not to be confused with

Elasticity, immediate return to the initial shape; fascial stiffness, a lasting increase in stiffness; hysteresis, a property of cycles that does not describe a static posture.

Related terms

Fascial gliding · Micro-movements

Sources and scope

• Yahia et al. (1993): viscoelastic properties of the human lumbodorsal fascia (J Biomed Eng)
• Adams and Dolan (1995): lumbar spine mechanics and their clinical significance (Clinical Biomechanics)