The Impact of Compressive Load Magnitude on the In-vitro Neutral Zone Range and Passive Stiffness during a Flexion-extension Range of Motion Test

INTRODUCTION The neutral zone, defined as the region of minimal passive stiffness [1], has been used to standardize the testing posture of functional spinal units (FSU) for in-vitro biomechanical studies. Typically, this region is determined experimentally through range of motion (ROM) tests, from which the applied moment and measured angular displacement are used to define the FSU’s passive stiffness. However, there is currently no standardized protocol that exists regarding the magnitude of compressive load that is applied during these tests [2]. As such, it has become increasingly difficult to make comparisons across studies since FSU test postures are typically defined using the experimental moment-angle data. The purpose of this study was to examine the impact of compressive load magnitude on passive flexion-extension (PFE) stiffness and neutral zone range. Considering previous research [3], it was hypothesized that increasing the magnitude of the compressive load would significantly change the passive stiffness of an FSU, resulting in different range of neutral zone.