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The Effect of Exertion Level on Activation Patterns and Variability of Trunk Muscles During Multidirectional Isometric Activities in Upright Posture

Talebian, Saeed, PhD*; Mousavi, Sayed Javad, PhD*; Olyaei, Gholam Reza, PhD*; Sanjari, Mohammad Ali, MSc; Parnianpour, Mohamad, PhD‡§

doi: 10.1097/BRS.0b013e3181bc34b5
Anatomy

Study Design. An experimental design to investigate activation patterns of trunk muscles during multidirectional exertions.

Objectives. To evaluate trunk muscle activation patterns in varying directions and moment magnitudes during an isometric task, and to investigate the effects of angle and level of isometric exertion on the electromyography (EMG) variability of trunk muscles in upright posture.

Summary of Background Data. Few studies have investigated trunk muscle activation patterns in multidirectional exertions with different moment magnitudes.

Methods. A total of 12 asymptomatic male subjects were participated in the study. The EMG activity of 10 selected trunk muscles was collected in the 3 seconds end point matching tasks in 8 angles and 3 magnitudes of exertion. Trunk muscle activation patterns were examined using EMG tuning curves and measuring preferred direction (mean vector direction) and the index of spatial focus. The effect of exertion level on these measures was investigated by Rao test. The effects of angle and level of exertion on the EMG variability of trunk muscles were tested by analysis of variance with repeated measures design.

Results. No significant difference in EMG tuning curves, preferred direction, and the index of spatial focus was found for each muscle studied across exertion levels (P > 0.05). The index of spatial focus of most muscles studied was not changed with increasing moment magnitude. EMG variability of trunk muscles was significantly affected by angle and level of exertion and their interaction effect (P < 0.001).

Conclusion. Consistent activation patterns of trunk muscles were found within and among subjects in different moment magnitudes. The index of spatial focus indicated that probably no shift to a higher cocontraction strategy has been adapted with increasing moment magnitude. The results suggested that increased EMG variability of trunk muscles in asymmetric exertions may be associated with lower trunk controllability during combined exertions.

Few studies have investigated trunk muscle activation patterns during multidirectional exertions. This study was performed to investigate activation patterns, spatial focus of electromyography activity as well as electromyography variability of 10 selected trunk muscles in different directions and levels of exertions.

From the *Department of Physical Therapy, Tehran University of Medical Sciences, Tehran, Iran; †Biomechanics Lab., Rehabilitation Research Center, Iran University of Medical Sciences, Tehran, Iran; ‡Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran; and §Department of Information and Industrial Engineering, Hanyang University, Ansan, Gyunggi, Republic of Korea.

Acknowledgment date: March 19, 2009. Revision date: June 14, 2009. Acceptance date: August 4, 2009.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Institutional funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Supported by Faculty of Rehabilitation Sciences, Tehran University of Medical Sciences grant no 86–01–32–5007, and partial support was provided by Hanyang University Research Foundation HY-2009-N9 for MP.

Address correspondence and reprint requests to Sayed Javad Mousavi, PhD, Department of Physical Therapy, Tehran University of Medical Sciences, Pich-e- Shemiran, Enghelab Ave., Tehran, Iran 11489–65141; E-mail: jmousavi@razi.tums.ac.ir

© 2010 Lippincott Williams & Wilkins, Inc.