Energetic and metabolic power demands of interchange and full-match players within National Rugby League match-play

Background: Mechanical time-motion models based upon running velocity have estimated the energetic demands of field-based team sports. Little, however, is known about how full-match and interchange players distribute their energetic demands throughout match-play. The purpose therefore is to describe and compare the metabolic demands of rugby league for interchange and full-match players. Methods: Eighteen elite rugby league players participated in this study. A time-motion model was used to estimate the energy expenditure and metabolic demands of rugby league match-play utilising Global Positioning System (GPS) technology. This approach uses a player's GPS velocity-time curve to estimate the positive/negative mechanical work done by the centre of mass in the horizontal/vertical planes, by the swinging-limbs and to overcome air-resistance. It's assumed the sum of these components is the total mechanical-work done due to locomotor demands. Players were categorized into positional groups: outside backs (OB), adjustables (ADJ), wide-running forwards (WRF) and hit-up forwards (HUF). Players were further categorized into full-match or interchange players. Match-play demands were enumerated by match time (min), relative distance (m.min⁻¹), acceleration/deceleration counts in moderate, high and very high zones (n.min⁻¹), energy expenditure (kJ.kg⁻¹), mean power (W.kg⁻¹), anaerobic index (arbitrary-unit) and equivalent distance (m).