Effect of fatigue on torque output and electromyographic measures of trunk muscles during isometric axial rotation.
OBJECTIVE
To examine the changes in torque output resulting from fatigue, as well as changes in electromyographic measures of trunk muscles during isometric axial rotation and to compare these changes between directions of axial rotation.


METHODS
Subjects performed fatiguing right and left isometric axial rotation of the trunk at 80% of maximum voluntary contraction while standing upright.


METHODS
A rehabilitation center.


METHODS
Twenty-three men with no history of back pain.


METHODS
Not applicable.


METHODS
Surface electromyographic signals were recorded from 6 trunk muscles bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were also measured.


RESULTS
During the fatiguing axial rotation contraction, coupling torques of both sagittal and coronal planes were slightly decreased and no difference was found between directions of axial rotation. Decreasing median frequency and an increase in electromyographic amplitude were also found in trunk muscles with different degrees of changes in individual muscles. There were significant differences (P<.05) between right and left axial rotation exertions in median frequency slope of external oblique, internal oblique, latissimus dorsi, and iliocostalis lumborum muscles, but no such difference was found in median frequency slope of rectus abdominis and multifidus muscles. This could be attributed to different functional roles among the muscles. Similar differences (P<.05) between right and left axial rotation in median frequency slope were also detected in the electromyographic amplitude slope of the trunk muscles. Coefficient of variation of the torque output and electromyographic activation in most of the trunk muscles increased during the fatigue process.


CONCLUSIONS
The changing coupling torque, different fatigue rate, and activation changes of trunk muscles, as well as the increase in variability during fatiguing axial rotation exertion, could affect the internal loading and stability of the spine; this needs to be further quantified in future studies.
Ng
Joseph K-F
JK
Department of Physiotherapy, University of Queensland, Australia. rsjoseph@polyu.edu.hk
Parnianpour
Mohamad
M
Richardson
Carolyn A
CA
Kippers
Vaughan
V
D000009:Abdominal Muscles / Q000502:physiology; D000328:Adult; D001676:Biofeedback, Psychology; D004576:Electromyography / Q000706:statistics & numerical data*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010775:Photic Stimulation; D012016:Reference Values; D012399:Rotation; D013997:Time Factors; D019415:Torque