An examination of innervation zone movement with increases in isometric torque production.
OBJECTIVE
To determine, with more precision than in previous investigations, if the innervation zone (IZ) for the biceps brachii can move with increases in isometric torque, and if so, whether or not that movement is influenced by differences in joint angle.


METHODS
Twenty-three participants (mean age=21.7 years) performed isometric contractions of the forearm flexors at 20, 40, 60, 80, and 100% of their maximal voluntary contraction (MVC) at three separate elbow joint angles (90, 120, and 150 degrees ). During each contraction, 16 channels of bipolar surface electromyographic (EMG) signals were recorded from the biceps brachii using a linear electrode array. For each joint angle, movement of the IZ with increases in torque was identified by a change in the EMG channel that was over the IZ.


RESULTS
For each joint angle, the IZ shifted proximally (2.3 channels) with increases in torque from 20 to 100% MVC. With an interelectrode distance of 2.5mm, this 2.3-channel shift reflects a 4.5-7.0mm movement of the IZ.


CONCLUSIONS
The IZ shifts proximally 4.5-7.0mm with increases in isometric torque, independent of joint angle.


CONCLUSIONS
These findings suggested that if isometric contractions are performed at different torque levels, the electrodes should be placed at least 7mm from the IZ.
Defreitas
Jason M
JM
Biophysics Laboratory, Department of Health and Exercise Science, University of Oklahoma, 1401 Asp Avenue, Norman, OK 73019, USA.
Costa
Pablo B
PB
Ryan
Eric D
ED
Herda
Trent J
TJ
Cramer
Joel T
JT
Beck
Travis W
TW
D000704:Analysis of Variance; D004551:Elbow Joint / Q000294:innervation*; D004576:Electromyography / Q000379:methods; D015444:Exercise; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009142:Musculoskeletal Physiological Phenomena; D016059:Range of Motion, Articular; D012815:Signal Processing, Computer-Assisted; D019415:Torque; D055815:Young Adult