Collision count in rugby union: A comparison of micro-technology and video analysis methods.

The aim of our study was to determine if there is a role for manipulation of g force thresholds acquired via micro-technology for accurately detecting collisions in rugby union. In total, 36 players were recruited from an elite Guinness Pro12 rugby union team. Player movement profiles and collisions were acquired via individual global positioning system (GPS) micro-technology units. Players were assigned to a sub-category of positions in order to determine positional collision demands. The coding of collisions by micro-technology at g force thresholds between 2 and 5.5 g (0.5 g increments) was compared with collision coding by an expert video analyst using Bland-Altman assessments. The most appropriate g force threshold (smallest mean difference compared with video analyst coding) was lower for all forwards positions (2.5 g) than for all backs positions (3.5 g). The Bland-Altman 95% limits of agreement indicated that there may be a substantial over- or underestimation of collisions coded via GPS micro-technology when using expert video analyst coding as the reference comparator. The manipulation of the g force thresholds applied to data acquired by GPS micro-technology units based on incremental thresholds of 0.5 g does not provide a reliable tool for the accurate coding of collisions in rugby union. Future research should aim to investigate smaller g force threshold increments and determine the events that cause coding of false positives.