Influence of body position and axial load on spinal stiffness in healthy young adults

Microgravity and Hypergravity Induced by Parabolic Flight Differently Affect Lumbar Spinal Stiffness

“…A possible explanation was that stiffness increase could be a reaction to the sudden change in gravity, which could have led to a safety co-contraction of the lumbar muscles that secured spinal integrity ( Swanenburg et al, 2018 ). We subsequently confirmed this HG response pattern in a larger study with 100 young, healthy volunteers by investigating changes in spinal stiffness during axial loading of the lumbar and thoracic spine ( Hausler et al, 2020 ). The results of these studies demonstrate the adaptability and complexity of the spinal motor control strategy and its dependency on differences in gravity or axial loading conditions.…”

“…With regard to muscle activity, increased activity of the local system, i.e., the muscles attaching to the lumbar vertebrae, would likely lead to increased spinal stiffness because the local system provides local mechanical stability of the lumbar spine ( Shirley et al, 1999 ; Stokes and Gardner-Morse, 2003 ). In contrast, activation of the global system leads to a load shift away from the spine toward the thoracic cage and the pelvis ( Bergmark, 1989 ); thereby decreasing spinal stiffness ( Swanenburg et al, 2018 ; Hausler et al, 2020 ). Because the in vivo assessment of spinal stiffness as performed here represents the net effect of all subsystems, it appears that the effects of the increased activation of the global muscle system dominated over the effects of the local muscle system and the flattening of the lumbar spine.…”

“…To measure this, we used an impulse head impactor mounted on an aluminum structure to which participants were strapped with a full-body harness. The “PulStar” a computer-a ssisted analytical device (Function Recording and Analysis System device PulStarFRAS, Sense Technology Inc., Pittsburgh, PA, United States) was mounted on the aluminum structure to measure the posterior-to-anterior spinal stiffness ( Figure 1 ; Leach et al, 2003 ; Hofstetter et al, 2018 ; Hausler et al, 2020 ). This device generates an 80 N impulse, which is applied to the L3 spinous process ( Swanenburg et al, 2018 ).…”

“…After the measurement, the valve on the air pump was opened so that the air could escape and the device returned to its starting position. To ensure that the impulse head was aligned precisely with the spinous process of L3, a portable ultrasound device (Aloka SSD-500 and Aloka UST-934N-3.5 Electronic Convex Probe; Aloka Co., Tokyo, Japan) was used ( Hausler et al, 2020 ). Figure 2 shows schematic of the measurement set-up.…”

In vivo measurements of spinal stiffness according to a stepwise increase of axial load

“…Such in vitro studies test the passive structures, including bones and ligaments, but they do not include muscle activity or motor control of the spine (Stokes and Gardner-Morse 2003 ; Gardner-Morse and Stokes 2003 ; Zhang et al 2020 ). Both the active and passive subsystems can be assessed by measuring spinal stiffness (Hausler et al 2020 ; Swanenburg et al 2018 , 2020 ). Spinal stiffness can be seen as a proxy for the resistance to deformation of all subsystems together in vivo (muscles, joints, and ligaments) to the energy infused by the impulse.…”