title: Validity of a Trunk-Mounted Accelerometer to Measure Physical Collisions in Contact Sports.
abstract: BACKGROUND
  Accelerometer peak impact accelerations are being used to measure player physical demands in contact sports. However, their accuracy to do so has not been ascertained.
  
  
  OBJECTIVE
  To compare peak-impact-acceleration data from an accelerometer contained in a wearable tracking device with a 3-dimensional motion-analysis (MA) system during tackling and bumping.
  
  
  METHODS
  Twenty-five semielite rugby athletes wore a tracking device containing a 100-Hz triaxial accelerometer (MinimaxX S4, Catapult Innovations, Australia). A single retroreflective marker was attached to the device, with its position recorded by a 12-camera MA system during 3 physical-collision tasks (tackle bag, bump pad, and tackle drill; N = 625). The accuracy, effect size, agreement, precision, and relative errors for each comparison were obtained as measures of accelerometer validity.
  
  
  RESULTS
  Physical-collision peak impact accelerations recorded by the accelerometer overestimated (mean bias 0.60 g) those recorded by the MA system (P < .01). Filtering the raw data at a 20-Hz cutoff improved the accelerometer's relationship with MA data (mean bias 0.01 g; P > .05). When considering the data in 9 magnitude bands, the strongest relationship with the MA system was found in the 3.0-g or less band, and the precision of the accelerometer tended to reduce as the magnitude of impact acceleration increased. Of the 3 movements performed, the tackle-bag task displayed the greatest validity with MA.
  
  
  CONCLUSIONS
  The findings indicate that the MinimaxX S4 accelerometer can accurately measure physical-collision peak impact accelerations when data are filtered at a 20-Hz cutoff frequency. As a result, accelerometers may be useful to measure physical collisions in contact sports.
authors: Centre for Exercise and Sport Science, Deakin University, Melbourne, Australia.
authors: Daniel W
authors: DW
authors: Wundersitz
authors: Paul B
authors: PB
authors: Gastin
authors: Samuel J
authors: SJ
authors: Robertson
authors: Kevin J
authors: KJ
authors: Netto
mesh_terms: D000054:Acceleration; D056044:Actigraphy / Q000295:instrumentation*; D000328:Adult; D056352:Athletes; D054874:Athletic Performance; D001696:Biomechanical Phenomena; D004867:Equipment Design; D005538:Football; D040362:Geographic Information Systems / Q000295:instrumentation*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009043:Motor Activity; D015203:Reproducibility of Results; D012420:Running; D012815:Signal Processing, Computer-Assisted; D013647:Task Performance and Analysis; D013997:Time Factors; D014741:Video Recording; D055815:Young Adult