Effects of vision and lumbar posture on trunk neuromuscular control

Abstract

The goal of this study was to determine the effects of vision and lumbar posture on trunk neuromuscular control. Torso perturbations were applied with a pushing device while the subjects were restrained at the pelvis in a kneeling-seated position. Torso kinematics and the muscle activity of the lumbar part of the M. Longissimus were recorded for 14 healthy subjects. Four conditions were included: a flexion, extension and neutral lumbar posture with eyes closed and the neutral posture with eyes open. Frequency response functions of the admittance and reflexes showed that there was no significant difference between the eyes open and eyes closed conditions, thereby confirming that vision does not play a role in the stabilization of the trunk during small-amplitude trunk perturbations. In contrast, manipulating posture did lead to significant differences. In particular, the flexed condition led to a lower admittance and lower reflex contribution compared to the neutral condition. Furthermore, the muscle pre-activation (prior to the onset of the perturbation) was significantly lower in the flexed posture compared to neutral. This confirms that flexing the lumbar spine increases the passive tissue stiffness and decreases the contribution of reflex activity to trunk control.

Prolonged Intermittent Trunk Flexion Increases Trunk Muscles Reflex Gains and Trunk Stiffness

“…The method used was proven reliable [28] and the reader is referred to previous publications for a detailed description of the procedure and related analyses [29,30]. In short, participants were positioned in a kneeling-seated position with their pelvis fixed (Fig 3).…”

“…The dynamic disturbance was a crested multi sine of 20 s duration, containing 18 logarithmically spaced frequency pairs with a bandwidth ranging from 0.2 to 15 Hz, repeated twice. To reduce adaptive behaviour to the high frequency content, the power above 4 Hz was reduced to 40% [29]. Participants did not receive direct visual feedback, but if drift from the initial position was observed by the investigator (via the real time visual information on the translation of the actuator) the participant was given verbal instruction to return to the initial position.…”

“…No feed-forward or voluntary activation was expected since the perturbations were perceived as random. In the final analysis, only the low frequencies (< 1.1 Hz) were included as the low frequency response reflects intrinsic stiffness and reflexive behaviour [29,30]. Trunk kinematics during perturbations were described in terms of translational movements of the pushing rod of the linear actuator.…”

Segmental trunk and head dynamics during frontal plane tilt stimuli in healthy sitting adults

“…These measures provide more information than standard time domain measures (e.g. root-mean-square, RMS), because the influence of neural and mechanical components may differ across frequencies (Goodworth and Peterka, 2010a; Maaswinkel et al, 2015; Oie et al, 2002; Peterka, 2003). Previous studies have shown body sway gains to decrease across a wide range of frequencies with increasing stimulus amplitude (Goodworth and Peterka, 2010b; Jeka et al, 2000; Peterka, 2002).…”

“…However, all of the above studies modeled the trunk or entire body in standing as a single-link inverted pendulum. Recently, a few studies have begun studying trunk control in a multi-segmental fashion (Butler et al, 2010; Maaswinkel et al, 2015; Preuss and Fung, 2008; Saavedra and Woollacott, 2015; Saavedra et al, 2012). We use a multi-segment analysis to explore gradation of sensorimotor control across head and trunk segments.…”