Metabolic power and energetic costs of elite Rugby League match-play

Background: Mechanical time-motion models based on running velocity have estimated the energy demands of field-based team sports. Such analyses have enhanced the understanding of the metabolic loads of match-play and aided in player preparation. The purpose of this study therefore is to describe the metabolic demands of different playing positions in elite rugby league match-play. Methods: A running based time-motion model was utilised to estimate the energy expenditure and metabolic demands of 18 elite rugby league players using 15Hz Global Positioning System (GPS) units. Briefly, this model 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 is assumed that 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). Game demands were quantified by match time (min), relative distance (m.min⁻¹), energy expenditure (kJ.kg⁻¹), mean power (W.kg⁻¹), anaerobic index (arbitrary-unit) and equivalent distance (m).