Abstract
Background. Motor unit firing frequencies are low during maximal voluntary contractions (MVCs) of human thenar muscles impaired by cervical spinal cord injury (SCI). Objective. This study aimed to examine whether thenar motor unit firing frequencies increase when driven by both maximal voluntary drive and other concurrent inputs compared with an MVC alone. Methods. Motor unit firing rates, force, and surface electromyographic activity (EMG) were compared across 2 contractions: (a) MVC alone and (b) MVC combined with another input (combination contraction). Other inputs (conditions) included vibration, heat, or cold applied to the anterior surface of the forearm, electrical stimulation delivered to the anterior surface of the middle finger, a muscle spasm, or a voluntary contraction of the contralateral thenar muscles against resistance. Results. The maximal firing frequency (n = 68 units), force, and electromyographic activity (n = 92 contraction pairs) were all significantly higher during the combined contractions compared with MVCs alone. There was a 3-way interaction between contraction, condition, and subject for maximal motor unit firing rates, force, and EMG. Thus, combined contraction responses were different for conditions across subjects. Some conditions (eg, a muscle spasm) resulted in more effective and more frequent responses (increases in unit firing frequency, force, EMG in >50% contractions) than others. Recruitment of new units also occurred in combined contractions. Conclusions. Motoneurons are still responsive to additional afferent inputs from various sources when rate modulation from voluntary drive is limited by SCI. Individuals with SCI may be able to combine inputs to control functional tasks they cannot perform with voluntary drive alone.
| Original language | English |
|---|---|
| Pages (from-to) | 58-67 |
| Number of pages | 10 |
| Journal | Neurorehabilitation and Neural Repair |
| Volume | 26 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 1 2012 |
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Keywords
- afferent input
- firing frequency
- motor unit
- persistent inward current
- recruitment
- spinal cord injury
ASJC Scopus subject areas
- Clinical Neurology
- Rehabilitation
- Neurology
Cite this
Do additional inputs change maximal voluntary motor unit firing rates after spinal cord injury? / Zijdewind, Inge; Gant, Katie; Bakels, Rob; Thomas, Christine K.
In: Neurorehabilitation and Neural Repair, Vol. 26, No. 1, 01.01.2012, p. 58-67.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Do additional inputs change maximal voluntary motor unit firing rates after spinal cord injury?
AU - Zijdewind, Inge
AU - Gant, Katie
AU - Bakels, Rob
AU - Thomas, Christine K
PY - 2012/1/1
Y1 - 2012/1/1
N2 - Background. Motor unit firing frequencies are low during maximal voluntary contractions (MVCs) of human thenar muscles impaired by cervical spinal cord injury (SCI). Objective. This study aimed to examine whether thenar motor unit firing frequencies increase when driven by both maximal voluntary drive and other concurrent inputs compared with an MVC alone. Methods. Motor unit firing rates, force, and surface electromyographic activity (EMG) were compared across 2 contractions: (a) MVC alone and (b) MVC combined with another input (combination contraction). Other inputs (conditions) included vibration, heat, or cold applied to the anterior surface of the forearm, electrical stimulation delivered to the anterior surface of the middle finger, a muscle spasm, or a voluntary contraction of the contralateral thenar muscles against resistance. Results. The maximal firing frequency (n = 68 units), force, and electromyographic activity (n = 92 contraction pairs) were all significantly higher during the combined contractions compared with MVCs alone. There was a 3-way interaction between contraction, condition, and subject for maximal motor unit firing rates, force, and EMG. Thus, combined contraction responses were different for conditions across subjects. Some conditions (eg, a muscle spasm) resulted in more effective and more frequent responses (increases in unit firing frequency, force, EMG in >50% contractions) than others. Recruitment of new units also occurred in combined contractions. Conclusions. Motoneurons are still responsive to additional afferent inputs from various sources when rate modulation from voluntary drive is limited by SCI. Individuals with SCI may be able to combine inputs to control functional tasks they cannot perform with voluntary drive alone.
AB - Background. Motor unit firing frequencies are low during maximal voluntary contractions (MVCs) of human thenar muscles impaired by cervical spinal cord injury (SCI). Objective. This study aimed to examine whether thenar motor unit firing frequencies increase when driven by both maximal voluntary drive and other concurrent inputs compared with an MVC alone. Methods. Motor unit firing rates, force, and surface electromyographic activity (EMG) were compared across 2 contractions: (a) MVC alone and (b) MVC combined with another input (combination contraction). Other inputs (conditions) included vibration, heat, or cold applied to the anterior surface of the forearm, electrical stimulation delivered to the anterior surface of the middle finger, a muscle spasm, or a voluntary contraction of the contralateral thenar muscles against resistance. Results. The maximal firing frequency (n = 68 units), force, and electromyographic activity (n = 92 contraction pairs) were all significantly higher during the combined contractions compared with MVCs alone. There was a 3-way interaction between contraction, condition, and subject for maximal motor unit firing rates, force, and EMG. Thus, combined contraction responses were different for conditions across subjects. Some conditions (eg, a muscle spasm) resulted in more effective and more frequent responses (increases in unit firing frequency, force, EMG in >50% contractions) than others. Recruitment of new units also occurred in combined contractions. Conclusions. Motoneurons are still responsive to additional afferent inputs from various sources when rate modulation from voluntary drive is limited by SCI. Individuals with SCI may be able to combine inputs to control functional tasks they cannot perform with voluntary drive alone.
KW - afferent input
KW - firing frequency
KW - motor unit
KW - persistent inward current
KW - recruitment
KW - spinal cord injury
UR - http://www.scopus.com/inward/record.url?scp=84856062480&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84856062480&partnerID=8YFLogxK
U2 - 10.1177/1545968311417449
DO - 10.1177/1545968311417449
M3 - Article
C2 - 21903974
AN - SCOPUS:84856062480
VL - 26
SP - 58
EP - 67
JO - Journal of Neurologic Rehabilitation
JF - Journal of Neurologic Rehabilitation
SN - 1545-9683
IS - 1
ER -