Publication date: Available online 22 November 2018
Source: Gait & Posture
Author(s): Tatsunori Watanabe, Ippei Nojima, Hideshi Sugiura, Basma Yacoubi, Evangelos A. Christou
Abstract
Background
Variability is an inherent feature of the motor output. Although low-frequency oscillations (<0.5 Hz) are the most important contributor to the variability of force during single-joint isolated force tasks, it remains unclear whether they contribute to the variability of a more complex task, such as a voluntary postural task.
Research question
Do low-frequency oscillations contribute to postural sway (center of pressure (COP) variability) when participants attempt to voluntarily maintain posture in a forward leaning position?
Methods
Fourteen healthy young adults performed two tasks: 1) stand quietly (control condition); 2) leaned their body forward to 60% of their maximum lean distance by dorsiflexing the ankle joint. We recorded the COP and electromyographic (EMG) activity from the medial gastrocnemius (MG) and soleus (SL) muscles. We quantified the following: 1) COP variability as the standard deviation (SD) of anteroposterior COP displacements; 2) modulation of COP as the power in COP displacements from 0-2 Hz; 3) modulation of EMG bursting as the power in the rectified and smoothed EMG from 0-2 Hz; 4) modulation of the interference EMG as the power in the EMG from 10-35 and 35-60 Hz.
Results
The SD of COP displacements related to the COP oscillations <0.5 Hz in both quiet standing and lean tasks. However, only for the lean task, the <0.5 Hz COP oscillations related to the EMG burst oscillations <0.5 Hz of the MG muscle. The EMG burst oscillations <0.5 Hz of the MG muscle further related to the interference EMG oscillations from 35-60 Hz for the lean task.
Significance
Voluntary control of forward leaning posture relates to low-frequency neural inputs to the MG muscle.
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