title: Effect of eccentric exercise-induced muscle damage on electromyographyic activity of quadriceps in untrained healthy females.
abstract: BACKGROUND
  The aim of this study was to investigate muscle damage indicators and electromyography activities of quadriceps muscles at 25° of hip flexion in untrained healthy females after an eccentric exercise induced muscle fiber damage.
  
  
  METHODS
  A total of 14 healthy females participated in this pre-experimental study. The subjects performed maximal eccentric quadriceps contractions at 25˚ of hip flexion. Maximum voluntary extensor isometric and concentric moments, angle of maximum moment for concentric contractions, perceived pain intensity, and pain pressure threshold were examined before, immediately, 48 hours, 120 hours and 14 days after eccentric exercise. Additionally, electromyography of three parts of quadriceps muscle, knee flexion range of motion and thigh circumference were measured before and after eccentric exercise.
  
  
  RESULTS
  Significant reductions in maximum isometric moment and maximum concentric moment were observed at angular velocity of 60˚ per sec immediately after eccentric exercise (p<0.05). Both maximum isometric moment and maximum concentric moment recovered to the baseline 48 hours after eccentric exercise. Increased pain intensity and decreased knee joint range of motion manifested 48 hours after eccentric exercise. Pain pressure threshold for the quadriceps was higher 14 days after exercise as compared to 48 and 120 hours (p<0.05). No significant changes observed in electromyography and thigh circumference (p>0.05).
  
  
  CONCLUSIONS
  Eccentric exercise performed at 25˚ of hip flexion resulted in muscle fiber injuries within the quadriceps muscle. However, electromyography of quadriceps muscle was not significantly different than the baseline. The result indicates that hip joint position may modify the effect of eccentric exercise on muscle activation.
authors.affiliation: 1. Assistant Professor, School ofRehabilitation, Tabriz University of Medical Sciences, Tabriz, Iran. mandana.rezae@gmail.com.
authors.forename: Mandana
authors.initials: M
authors.lastname: Rezaei
authors.affiliation: 2. Professor, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran, Rehabilitation Research Center, Biomechanics Lab, Iran University of Medical Sciences, Tehran, Iran. ebrahimi.pt@gmail.com.
authors.forename: Ismael
authors.initials: I
authors.lastname: Ebrahimi-Takamjani
authors.affiliation: 3. Assistant Professor, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran, Rehabilitation Research Center, Biomechanics Lab, Iran University of Medical Sciences, Tehran, Iran. aliajamshidi@yahoo.com.
authors.forename: Ali A
authors.initials: AA
authors.lastname: Jamshidi
authors.affiliation: 4. Assistant Professor, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran, Rehabilitation Research Center, Biomechanics Lab, Iran University of Medical Sciences, Tehran, Iran. vasaghib@tums.ac.ir.
authors.forename: Behnoush
authors.initials: B
authors.lastname: Vassaghi-Gharamaleki
authors.affiliation: 5. Assistant Professor, Department of Physical Education and Sport Science, University of Bojnord, Bojnord, Iran. nhedayatpour@yahoo.com.
authors.forename: Nosratollah
authors.initials: N
authors.lastname: Hedayatpour
authors.affiliation: 6. PhD Student, Department of Occupational Therapy, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran. naser_havaei@yahoo.com.
authors.forename: Naser
authors.initials: N
authors.lastname: Havaei
keywords: Muscles; electromyography; exercise; hip; muscle soreness