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Front. Hum. Neurosci. | doi: 10.3389/fnhum.2018.00254

Age-related declines in the ability to modulate common input to bilateral and unilateral plantar flexors during forward postural lean

 Tatsunori Watanabe1, 2*, Kotaro Saito1, Kazuto Ishida1,  Shigeo Tanabe3 and  Ippei NOJIMA1
  • 1Department of Physical Therapy, Nagoya University Graduate School of Medicine, Japan
  • 2Japan Society for the Promotion of Science (JSPS), Japan
  • 3Faculty of Rehabilitation, School of Health Sciences, Fujita Health University, Japan

Aging can impair an ability to lean the body forward to the edge of the base of support. Here, we investigated, using a coherence analysis, common inputs to bilateral and unilateral plantar flexor muscles to test a hypothesis that the age-related impairment would be related to strong synchronous bilateral activation and reduced cortical control of these muscles. Healthy young (n = 14) and elderly adults (n =19), who were all right-foot dominant, performed quiet standing task and tasks that required the subjects to lean their body forward to 35% and 75% of the maximum lean distance. The electromyogram was recorded from the bilateral medial gastrocnemius (MG) and soleus (SL) muscles. We analyzed delta-band coherence, that reflects comodulation of muscle activity, between the bilateral homologous muscles (MG-MG and SL-SL pairs). The origin of this bilateral comodulation is suggested to be the subcortical system. Also, we examined beta-band coherence, that is related to the corticospinal drive, between the unilateral muscles (MG-SL pair) in the right leg. Results indicated that the bilateral delta-band coherence for the MG-MG pair was significantly smaller in the 75% forward lean than quiet standing and 35 % forward lean tasks for the young adults (quiet: p = 0.036; 35%: p = 0.0011). The bilateral delta-band coherence for the SL-SL pair was significantly smaller in the 75% forward lean than 35% forward lean task for the young adults (p = 0.027). Furthermore, the unilateral beta-band coherence was larger in the forward lean than quiet standing task for the young adults (35%: p < 0.001; 75%: p = 0.029). Contrarily, the elderly adults did not demonstrate such changes. These findings suggest the importance of decreasing the synchronous bilateral activation and increasing the unilateral cortical control of the plantar flexor muscles for the successful forward postural lean performance, and that aging impairs this modulatory ability.

Keywords: EMG coherence, Plantar flexors, common input, balance, Aging, forward postural lean

Received: 21 Feb 2018; Accepted: 04 Jun 2018.

Edited by:

Yusuf O. Cakmak, University of Otago, New Zealand

Reviewed by:

Imran K. Niazi, Centre for Chiropractic Research, New Zealand College of Chiropractic, New Zealand
KEMAL S. TURKER, Koç University, Turkey  

Copyright: © 2018 Watanabe, Saito, Ishida, Tanabe and NOJIMA. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mr. Tatsunori Watanabe, Nagoya University Graduate School of Medicine, Department of Physical Therapy, 1-1-20 Daiko-Minami, Higashi-ku, Nagoya, 461-8673, Acihi, Japan, watanabe.tatsunori@h.mbox.nagoya-u.ac.jp