The effects of dietary carbohydrate on muscle glycogen metabolism and performance in an 80 minute rugby simulation
Kearney, Glenn Antony
Rugby union forward play is characterised by intense, intermittent periods of exercise requiring high levels of aerobic fitness and substantial anaerobic power. The effects of a high and low carbohydrate diet for the three days preceding a simulation trial were studied in 10 male rugby forwards (23 ± 4 yr, 189 ± 7 cm, 96 ± 9 kg). A randomised, cross-over protocol involving two 80 min rugby simulation trials, separated by one week, was used. Subjects consumed either a high carbohydrate (HCHO) diet (>8 g.kg-1) or a low carbohydrate (LCHO) diet (<4 g.kg-1). Vastus lateralis biopsies were taken before and after each simulation trial. Resting muscle glycogen concentration was higher following the HCHO treatment than LCHO treatment (102 ± 28, 59 ± 17 mmol.kg-1 ww; resp-, p=0.002) indicating that the dietary prescription was adhered to. The HCHO dietary treatment resulted in greater glycogen utilisation than the LCHO dietary treatment (54 ± 13, 33 ± 15 mmol.kg-1 ww; resp-, p=0.02). Performance in the simulation was determined by measuring the ability of the subjects to perform high intensity, rugby specific tasks (e.g., mauling, scrummaging, and sprinting). Each individual was assessed against his own personal best, and each task was also given a weighting depending on the contribution it has to match play. A resultant performance score (TWS) was calculated for each lap of the simulation. The difference in the TWS from the first-half to the second-half between the two treatments (HCHO-LCHO) was 4.0 units (or 4.5%), the interaction effect between treatment, and game halves, narrowly failed to attain statistical significance (p=0.08; effect size = 0.7). This result may have relevant practical implications, especially considering the simulation was found to be less intense (based on HR and BLa measurements) than match play. In conclusion, the rugby simulation resulted in a large amount of glycogen utilisation, and despite the limitations of the performance instrument, and the small sample size, it appears that CHO intake in the days leading up to a match may influence the onset of fatigue in rugby forwards.
Advisor: Rehrer, Nancy; Thomson, Christine
Degree Name: Master of Science
Degree Discipline: Human Nutrition
Publisher: University of Otago
Research Type: Thesis