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

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 +/- 12 kg, height 180 +/- 8 cm) professional players completed a RL match after 36-h consuming a non-isocaloric high carbohydrate (n = 8; 6 g kg day(-1)) or low carbohydrate (n = 8; 3 g kg day(-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 +/- 81 mmol kg(-1) d.w.) were unclear. High (243 +/- 43 mmol kg(-1) d.w.) and low carbohydrate groups (298 +/- 130 mmol kg(-1) d.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 +/- 0.39 mmol l(-1) and 1.45 +/- 0.51 mmol l(-1), respectively), whereas differences between the 2 groups for glycerol were unclear (98.1 +/- 33.6 mmol l(-1) and 123.1 +/- 39.6 mmol l(-1)) in the high and low carbohydrate groups, respectively. Conclusions: Professional RL players can utilise similar to 40% of their muscle glycogen during a competitive match regardless of their carbohydrate consumption in the preceding 36-h. (C) 2016 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.