Effects of experimentally induced cervical spine mobility alteration on the postural organisation of gait initiation

Abstract

Gait initiation (GI), the transient period between quiet standing and locomotion, is a functional task classically used in the literature to investigate postural control. This study aimed to investigate the influence of an experimentally-induced alteration of cervical spine mobility (CSM) on GI postural organisation. Fifteen healthy young adults initiated gait on a force-plate in (1) two test conditions, where participants wore a neck orthosis that passively simulated low and high levels of CSM alteration; (2) one control condition, where participants wore no orthosis; and (3) one placebo condition, where participants wore a cervical bandage that did not limit CSM. Centre-of-pressure and centre-of-mass kinematics were computed based on force-plate recordings according to Newton's second law. Main results showed that anticipatory postural adjustments amplitude (peak backward centre-of-pressure shift and forward centre-of-mass velocity at toe-off) and motor performance (step length and forward centre-of-mass velocity at foot-contact) were altered under the condition of high CSM restriction. These effects of CSM restriction may reflect the implementation of a more cautious strategy directed to attenuate head-in-space destabilisation and ease postural control. It follows that clinicians should be aware that the prescription of a rigid neck orthosis to posturo-deficient patients could exacerbate pre-existing GI deficits.

Figure 1

Typical biomechanical traces in the Control condition and the GI-high condition (gait initiation with a high level of cervical spine mobility restriction). Traces reported in each condition are obtained from the same participant performing one single trial. Anteroposterior (AP) direction. x’M_TO, x’M_FC: centre-of-mass (COM) velocity at toe-off and foot-contact. xPmax: peak of backward centre-of-pressure (COP) shift during APA. F forward; B backward. Mediolateral (ML) direction. y’M_TO, y’M_FC: COM velocity at toe-off and foot-contact. yPmax: peak of ML COP shift during APA. ST: stance limb; SW: swing limb. Vertical direction. z’M_min, z’M_FC: peak of negative vertical COM velocity and COM velocity at foot-contact. D downward; U upward. Vertical dashed lines: t0 onset variation of biomechanical traces; HO swing heel-off; TO swing toe-off, FC swing foot-contact. Horizontal arrows: QS quiet standing, APA anticipatory postural adjustments; FL: swing foot-lift; EXE execution phase of gait initiation.

Figure 2

Effects of the condition on selected APA and foot-lift parameters. Reported are mean values (all participants together) + 1 SD. APA anticipatory postural adjustments, AP anteroposterior, COP centre-of-pressure, COM centre-of-mass, TO swing toe-off; *, **: significant difference between bars with p < 0.05 and p < 0.01, respectively.

Figure 3

Effects of the condition on motor performance (upper panels) and stability parameters (bottom panels). Reported are mean values (all participants together) + 1 SD. AP, ML anteroposterior, mediolateral; COM centre-of-mass; FC foot-contact; *, **: significant difference between bars with p < 0.05 and p < 0.01, respectively.

Figure 4

Cervical collars used in the placebo condition (A; jersey tubular bandage), the GI-low condition (B; foam flexible orthosis) and the GI-high condition (C; rigid orthosis).