Motor unit recruitment in the trapezius muscle with special reference to coarse arm movements.
Journal article, 2001
Chronic shoulder pain is common in a variety of occupations. The "Cinderella hypothesis" suggests that the pain originates from damaged type I muscle fibres driven into degenerative processes as a result of too long activation and too short recovery time. The main purpose of this study was to investigate if the same motor units are active during all phases of coarse arm movements. Eight healthy volunteers participated in the study. Intramuscular electromyographic signals were picked up with a four-lead fine wire electrode, during a unilateral straight arm movement. The movement started with either (part 1) an abduction or a flexion, then (2) a movement in the horizontal plane from the sagittal to the frontal plane or vice versa, and finally (3) an adduction or an extension to the start position. The movement cycle was performed in three different speeds, slow, medium, and high, with one, two or five cycles per 20 s, respectively. On an average, the motor unit action potentials (MUAPs) of 6 motor units (range, 1-15) were identified per trail. In total 94% of the MUAP trains that were identified showed firings in all 3 parts of the movements. The findings support the Cinderella hypothesis, although there is a need to further investigate the temporal pattern of long-term motor unit activity.
Adult
Electromyography
Recruitment
Movement
Skeletal
physiology
Female
Neurophysiological
Muscle
Action Potentials
physiology
physiology
Humans
Arm
Motor Neurons
Shoulder
Muscle Fibers
innervation
Male
Skeletal
physiology
Author
Mikael Forsman
Department of Human Factors Engineering
L Birch
Qiuxia Zhang
University of Gothenburg
Roland Kadefors
University of Gothenburg
Journal of Electromyography and Kinesiology
1050-6411 (ISSN) 1873-5711 (eISSN)
Vol. 11 3 207-16Subject Categories
Orthopedics
PubMed
11335151