title: Scapulothoracic latent muscle reaction timing comparison between trained overhead throwers and untrained control subjects.
abstract: OBJECTIVE
  This study evaluated select scapulothoracic muscles for training-induced latent muscle reaction timing (LMRT) changes. Comparisons were also made between the dominant and non-dominant upper extremities and between individual muscles.
  
  
  METHODS
  Fifteen male trained overhead throwers (college baseball pitchers) and 15 male untrained, age-matched control subjects participated in this study. Scapulothoracic muscle activation data were collected as subjects attempted to stop a variably timed, sudden glenohumeral joint internal rotation perturbation.
  
  
  RESULTS
  Training group differences were not evident for LMRT (P=0.56), however upper extremity dominance (P=0.003) and test muscle (P=0.0002) displayed significant differences. Dominant upper extremity upper trapezius muscle LMRT (72.5+/-26 ms) occurred later than non-dominant upper trapezius muscle LMRT (60.0+/-14.1 ms, P=0.001). Dominant upper extremity middle trapezius-rhomboid muscle LMRT (60.0+/-16.2 ms) occurred later than non-dominant middle trapezius-rhomboid muscle LMRT (50.2+/-12.6 ms, P=0.004). Dominant upper extremity upper trapezius muscle LMRT also occurred later than serratus anterior (55.7+/-16.0 ms, P=0.001) and middle trapezius-rhomboid LMRT (60.2+/-16 ms, P=0.003). Mean overall dominant upper extremity LMRT (62.7+/-19.4 ms) was delayed compared with mean overall non-dominant upper extremity LMRT (53.9+/-12.4 ms, P=0.003).
  
  
  CONCLUSIONS
  Although training was not found to influence scapulothoracic LMRT, differences were observed between the dominant and non-dominant upper extremities. Consistent LMRT delays at the dominant upper extremity suggest possible neuromuscular timing differences to enable prolonged glenohumeral joint and scapulothoracic articulation acceleration before deceleration through eccentric muscle activation. Both trained and untrained overhead throwers displayed this response. Variable perturbation test velocities, and in-season testing of larger subject groups may be needed to better elucidate the more subtle differences associated with training.
authors.affiliation: Physical Disabilities Branch, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Brindle
authors.forename: J A
authors.initials: JA
authors.lastname: Nyland
authors.forename: A J
authors.initials: AJ
authors.lastname: Nitz
authors.forename: R
authors.initials: R
authors.lastname: Shapiro
mesh_terms: D000293:Adolescent; D000328:Adult; D001484:Baseball; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal; D011930:Reaction Time; D012540:Scapula / Q000502:physiology*; D013909:Thorax / Q000502:physiology*; D014481:United States