Micro-movements

Scientific basis

Studies show that different sitting postures and pelvic rotations are accompanied by different pressure distributions at the body–seat interface. They do not necessarily measure the micro-movements defined here, and they do not show that a small amplitude, on its own, produces a clinical benefit.

In synovial cells studied in the laboratory, Raïf et al. observed that cyclic stress modifies the expression of proteins involved in matrix remodeling, including MMP-3. In three-dimensional tissue analogs containing fibroblasts, Jacho et al. observed different responses depending on the amplitude of the applied strain. These experimental models document cellular sensitivity to mechanical stress; they demonstrate neither the maintenance of fascia by seated micro-movements nor a clinical effect on pain.

Blue Portance / SBNFA™ reading

In SBNFA™, a micro-movement takes on its meaning through the function it enables: continuously exploring close variations of balance, adjusting the organization of the pelvis and body segments, varying the points of support and contributing to continuous postural regulation. The continuity of these discreet adjustments throughout the day is one dimension of the Blue Portance reading. The link with mechanotransduction is an integration hypothesis of the framework, not a direct demonstration from the cellular studies. Movement and adaptability are not synonyms. In the framework, sacroiliac micro-rotation, which combines nutation, counternutation and lateral tilting, is one form of micro-movement.

Contribution to the analysis of sitting

The analysis looks at whether small voluntary or spontaneous adjustments are possible, whether they vary the points of support and whether they take place within a continuous balance space. Micro-movements can then contribute to adaptive potential and to stable dynamic sitting, in which it is the body that stabilizes itself. An imposed movement or instability can produce displacements without serving these adjustments.

Not to be confused with

Postural variability, which describes the distribution of these movements over time; a large-amplitude postural change; an oscillation imposed by the support surface; a demonstrated clinical benefit.

Related terms

Postural variability · Sacral nutation and counternutation · Postural adaptability

Sources and scope

• Hobson (1992): posture, pressure and shear at the body–seat interface, particularly in wheelchair users
• Moes (2007): pelvic rotation and pressure distribution on a rigid support
• Raïf et al. (2008): effect of cyclic stress on MMP-1 and MMP-3 expression in synovial cells
• Jacho et al. (2022): fibroblast response to several strain amplitudes in a three-dimensional tissue analog