Tatsunori Watanabe1, Ippei Nojima2, Hideshi Sugiura2, Basma Yacoubi3, Evangelos A Christou4. 1. Department of Physical Therapy, Nagoya University Graduate School of Medicine, Nagoya, Aichi, 461-8673, Japan; Japan Society for the Promotion of Science, Tokyo, Japan; Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA. Electronic address: tawatanabe@outlook.com. 2. Department of Physical Therapy, Nagoya University Graduate School of Medicine, Nagoya, Aichi, 461-8673, Japan. 3. Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA. 4. Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA; Department of Physical Therapy, University of Florida, Gainesville, FL, USA. Electronic address: eachristou@hhp.ufl.edu.
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 to 2 Hz; 3) modulation of EMG bursting as the power in the rectified and smoothed EMG from 0 to 2 Hz; 4) modulation of the interference EMG as the power in the EMG from 10 to 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 to 60 Hz for the lean task. SIGNIFICANCE: Voluntary control of forward leaning posture relates to low-frequency neural inputs to the MG muscle.
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 to 2 Hz; 3) modulation of EMG bursting as the power in the rectified and smoothed EMG from 0 to 2 Hz; 4) modulation of the interference EMG as the power in the EMG from 10 to 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 to 60 Hz for the lean task. SIGNIFICANCE: Voluntary control of forward leaning posture relates to low-frequency neural inputs to the MG muscle.
Authors: Anna Kamieniarz; Justyna Michalska; Wojciech Marszałek; Magdalena Stania; Kajetan J Słomka; Agnieszka Gorzkowska; Grzegorz Juras; Michael S Okun; Evangelos A Christou Journal: PLoS One Date: 2021-01-12 Impact factor: 3.240