Muscle glycogen availability is a determinant of endurance exercise performance and its depletion results in fatigue. We have demonstrated that 5 days of creatine (Cre; 20g/day) and simple carbohydrate (CHO) ingestion augmented muscle glycogen storage following exhaustive exercise in man when compared to CHO feeding alone (Robinson et al. 1999). This study characterises the time-course of this Cre-induced glycogen super-compensatory response, and points to mechanisms underpinning this phenomenon.

Fourteen recreationally-trained males (age 26.4 ± 2.0 years, BMI 24.5 ± 1.0, Î{special}J{special}_,max 44.4 ± 1.5 ml kg^-1 min^-1) participated in this study, which was approved by the local Ethics Committee. Subjects reported fasted to the laboratory, whereupon they underwent a 2 h oral-glucose tolerance test (GTT, 90 g CHO; blood sampling every 15 min for serum insulin analysis). Following GTT, subjects exercised at 70 % Î{special}J{special}_,max on a cycle ergometer until exhaustion. Following exercise, a muscle biopsy sample was obtained from the subject’s non-dominant leg (Exhaustion). Subjects were then randomly assigned to a Cre (n = 7) or glycine (placebo, n = 7) treatment group and ingested 5 g of Cre or 5 g of glycine dissolved in 250 ml of a warm sugar-free solution followed by 500 ml of a CHO-containing solution (90 g simple sugars). Subjects continued to ingest these solutions, at equally spaced intervals, on 4 occasions per day over 6 days. A high CHO diet (37.5 kcal kg^-1 day-1, >80 % calorific intake CHO) was provided and ingested during the supplementation period. Subjects reported fasted to the laboratory on days 1, 3 and 6 of supplementation for further GTTs and muscle biopsy sampling from their non-dominant leg. Muscle samples were immediately frozen in liquid nitrogen, freeze dried and used for subsequent biochemical analysis (Table 1). Data are expressed as means ± S.E.M. Statistical analysis was performed using two-way ANOVA with LSD post-hoc analysis.

The present study unequivocally establishes Cre’s glycogen super-compensatory properties and shows that this marked response occurs within 24-hours post-exercise, during which the muscle total-Cre stores had increased < 10 %. Furthermore, Cre augments muscular glycogen stores independent of any clear increase in serum insulin AUC (area under the curve) during 6 days of supplementation, which points towards some other mechanism as being causative.

This work was carried out as part of the Chemical Biological Defence & Human Sciences Domain of the UK MoD Corporate Research Programme