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Year : 2019  |  Volume : 62  |  Issue : 4  |  Page : 166-174

The effect of visuospatial resolution on discharge variability among motor units and force–discharge relation

1 Department of Physical Therapy, Chung Shan Medical University; Physical Therapy Room, Chung Shan Medical University Hospital, Taichung City, Taiwan
2 Department of Rehabilitation Medicine, Tainan Municipal An-Nan Hospital, Tainan, Taiwan
3 Physical Education Office, Asian University, Taichung City, Taiwan
4 Institute of Allied Health Sciences; Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan City, Taiwan

Correspondence Address:
Prof. Ing-Shiou Hwang
Institute of Allied Health Sciences, College of Medicine, National Cheng Kung University, Tainan City
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/CJP.CJP_12_19

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Although force steadiness varies with visuospatial information, accountable motor unit (MU) behaviors are not fully understood. This study investigated the modulation of MU discharges and force–discharge relation due to variations in the spatial resolution of visual feedback, with a particular focus on discharge variability among MUs. Fourteen young adults produced isometric force at 10% of maximal voluntary contraction (MVC) through index abduction, under the conditions of force trajectory displayed with low visual gain (LVG) and high visual gain (HVG). Together with smaller and more complex force fluctuations, HVG resulted in greater variabilities of the mean interspike interval and discharge irregularity among MUs than LVG did. Estimated via smoothening of a cumulative spike train of all MUs, global discharge rate was tuned to visual gain, with a more complex global discharge rate and a lower force–discharge relation in the HVG condition. These higher discharge variabilities were linked to larger variance of the common drive received by MUs for regulation of muscle force with higher visuospatial information. In summary, higher visuospatial information improves force steadiness with more complex force fluctuations, underlying joint effects of low-pass filter property of the musculotendon complex and central modulation of discharge variability among MUs.

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