Muscle glycogen utilisation during Rugby match play: Effects of pre-game carbohydrate.

ABSTRACT

OBJECTIVES: Although the physical demands of Rugby League (RL) match-play are well-known, the fuel sources supporting energy-production are poorly understood. We therefore assessed muscle glycogen utilisation and plasma metabolite responses to RL match-play after a relatively high (HCHO) or relatively low CHO (LCHO) diet. DESIGN: Sixteen (mean±SD age; 18±1 years, body-mass; 88±12kg, height 180±8cm) professional players completed a RL match after 36-h consuming a non-isocaloric high carbohydrate (n=8; 6gkgday-1) or low carbohydrate (n=8; 3gkgday-1) diet. METHODS: Muscle biopsies and blood samples were obtained pre- and post-match, alongside external and internal loads quantified using Global Positioning System technology and heart rate, respectively. Data were analysed using effects sizes ±90% CI and magnitude-based inferences. RESULTS: Differences in pre-match muscle glycogen between high and low carbohydrate conditions (449±51 and 444±81mmolkg-1d.w.) were unclear. High (243±43mmolkg-1d.w.) and low carbohydrate groups (298±130mmolkg-1d.w.) were most and very likely reduced post-match, respectively. For both groups, differences in pre-match NEFA and glycerol were unclear, with a most likely increase in NEFA and glycerol post-match. NEFA was likely lower in the high compared with low carbohydrate group post-match (0.95±0.39mmoll-1 and 1.45±0.51mmoll-1, respectively), whereas differences between the 2 groups for glycerol were unclear (98.1±33.6mmoll-1 and 123.1±39.6mmoll-1) in the high and low carbohydrate groups, respectively. CONCLUSIONS: Professional RL players can utilise ∼40% of their muscle glycogen during a competitive match regardless of their carbohydrate consumption in the preceding 36-h.