Modulation of motor unit activity in biceps brachii by neuromuscular electrical stimulation applied to the contralateral arm.
The purpose of the study was to determine the influence of neuromuscular electrical stimulation (NMES) current intensity and pulse width applied to the right elbow flexors on the discharge characteristics of motor units in the left biceps brachii. Three NMES current intensities were applied for 5 s with either narrow (0.2 ms) or wide (1 ms) stimulus pulses: one at 80% of motor threshold and two that evoked contractions at either ∼10% or ∼20% of maximal voluntary contraction (MVC) force. The discharge times of 28 low-threshold (0.4-21.6% MVC force) and 16 high-threshold (31.7-56.3% MVC force) motor units in the short head of biceps brachii were determined before, during, and after NMES. NMES elicited two main effects: one involved transient deflections in the left-arm force at the onset and offset of NMES and the other consisted of nonuniform modulation of motor unit activity. The force deflections, which were influenced by NMES current intensity and pulse width, were observed only when low-threshold motor units were tracked. NMES did not significantly influence the discharge characteristics of tracked single-threshold motor units. However, a qualitative analysis indicated that there was an increase in the number of unique waveforms detected during and after NMES. The findings indicate that activity of motor units in the left elbow flexors can be modulated by NMES current and pulse width applied to right elbow flexors, but the effects are not distributed uniformly to the involved motor units.
Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Thessaloniki, Greece; jamoirid@phed-sr.auth.gr.
Ioannis G
IG
Amiridis
Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and.
Diba
D
Mani
Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and Department of Basic Medical Sciences, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia.
Awad
A
Almuklass
Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and.
Boris
B
Matkowski
Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and.
Jeffrey R
JR
Gould
Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and.
Roger M
RM
Enoka
D000293:Adolescent; D000328:Adult; D001132:Arm / Q000294:innervation* / Q000502:physiology; D004550:Elbow / Q000294:innervation / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D055815:Young Adult
biceps brachii; crossed effects; motor unit; neuromuscular electrical stimulation; pulse width