title: A comparison of time-motion analysis methods for field based sports.
abstract: OBJECTIVE
  To assess the validity of a digitizing time-motion-analysis method for field-based sports and compare this with a notational-analysis method using rugby-union match play.
  
  
  METHODS
  Five calibrated video cameras were located around a rugby pitch, and 1 subject completed prescribed movements within each camera's view. Running speeds were measured using photocell timing gates. Two experienced operators digitized video data (operator 1 on 2 occasions) to allow 2-dimensional reconstruction of the prescribed movements.
  
  
  RESULTS
  Accuracy for total distance calculated was within 2.1% of the measured distance. For intraoperator and interoperator reliability, calculated distances were within 0.5% and 0.9%, respectively. Calculated speed was within 8.0% of measured photocell speed with intraoperator and interoperator reliability of 3.4% and 6.0%, respectively. For the method comparison, two 20-minute periods of rugby match play were analyzed for 5 players using the digitizing method and a notational time-motion method. For the 20-minute periods, overall mean absolute differences between methods for percentage time spent and distances covered performing different activities were 3.5% and 198.1 +/- 138.1 m, respectively. Total number of changes in activity per 20 minutes were 184 +/- 24 versus 458 +/- 48, and work-to-rest ratios, 10.0%:90.0% and 7.3%:92.7% for notational and digitizing methods, respectively.
  
  
  CONCLUSIONS
  The digitizing method is accurate and reliable for gaining detailed information on work profiles of field-sport participants and provides applied researchers richer data output than the conventional notational method.
authors.affiliation: Sport and Exercise Science, School for Heatlh, University of Bath, Bath, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Roberts
authors.forename: Grant
authors.initials: G
authors.lastname: Trewartha
authors.forename: Keith
authors.initials: K
authors.lastname: Stokes
mesh_terms: D054874:Athletic Performance; D001696:Biomechanical Phenomena; D005538:Football; D006801:Humans; D008297:Male; D015588:Observer Variation; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013996:Time and Motion Studies; D014142:Track and Field; D014741:Video Recording