title: The impact of load and base of support on electromyographic onset in the shoulder muscle during push-up exercises.
abstract: OBJECTIVE
  To investigate the effects of base of support (BOS) and external loads on electromyographic (EMG) onset in the shoulder muscles during push-up exercises.
  
  
  METHODS
  Two levels of external load were applied at two levels of BOS stability during push-up exercises. EMG onset in six shoulder muscles was measured in 30 healthy participants.
  
  
  RESULTS
  With load set at 4% of body weight (BW), EMG onset in the lower trapezius (LT) (P = 0.003) and biceps brachia (BB) (P = 0.001) was significantly decreased with no load. Conversely, in other muscles (the upper trapezius (UT), teres major (TM), seratus anterior (SA) and deltoid posterior (DP)), time to EMG onset did not change significantly. No significant changes in EMG onset were observed with load at 2% of BW. The average time to EMG onset was significantly decreased for different stages of BOS instability in the LT (P = 0.04) and UT (P = 0.001).
  
  
  CONCLUSIONS
  Both load and BOS instability reduce time to EMG onset, but BOS instability produces greater reductions.
authors.affiliation: Department of Physiotherapy, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Peninsula Campus, Melbourne, VIC 3800, Australia. bita.vaseghi@monash.edu
authors.forename: Bita
authors.initials: B
authors.lastname: Vaseghi
authors.forename: Shapour
authors.initials: S
authors.lastname: Jaberzadeh
authors.forename: Khosro Khademi
authors.initials: KK
authors.lastname: Kalantari
authors.forename: Sedigheh Sadat
authors.initials: SS
authors.lastname: Naimi
mesh_terms: D000293:Adolescent; D000328:Adult; D057645:Deltoid Muscle / Q000502:physiology*; D004576:Electromyography / Q000379:methods / Q000592:standards; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D015203:Reproducibility of Results; D012782:Shoulder / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult