title: The effect of exertion level on activation patterns and variability of trunk muscles during multidirectional isometric activities in upright posture.
abstract: METHODS
  An experimental design to investigate activation patterns of trunk muscles during multidirectional exertions.
  
  
  OBJECTIVE
  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.
  
  
  BACKGROUND
  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).
  
  
  CONCLUSIONS
  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 co-contraction 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.
authors.affiliation: Department of Physical Therapy, Tehran University of Medical Sciences, Pich-e-Shemiran, Enghelab Avenue, Tehran, Iran.
authors.forename: Saeed
authors.initials: S
authors.lastname: Talebian
authors.forename: Sayed Javad
authors.initials: SJ
authors.lastname: Mousavi
authors.forename: Gholam Reza
authors.initials: GR
authors.lastname: Olyaei
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Sanjari
authors.forename: Mohamad
authors.initials: M
authors.lastname: Parnianpour
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted