Author(s): FUCHS, C., VEERAIAH, P., HERMANS, W.J.H., BRAUWERS, B., VONCKEN, R., PETRICK, H.L., HENDRIKS, F.K., BELS, J.L.M., VAN DEN HURK, J., WEBER, J., SENDEN, J.M., THELWALL, P.E., PROMPERS, J.J., VAN LOON, L.J.C., Institution: MAASTRICHT UNIVERSITY, Country: NETHERLANDS, Abstract-ID: 1866

INTRODUCTION:
Both liver and muscle glycogen contribute substantially to energy requirements during prolonged moderate- to high-intensity exercise. Carbohydrate intake after exercise is essential to replenish both liver and muscle glycogen stores. Consuming ample carbohydrates has shown to replenish muscle glycogen concentrations within 24 h following exhaustive cycling. Yet, the time required to replenish liver glycogen after exercise in vivo in humans remains to be determined.
METHODS:
Twelve well-trained male cyclists (age: 25±5 y; VO2peak: 67±5 mL/kg/min; Wmax: 5.8±0.7 W/kg) completed two test days in a randomized cross-over fashion. On both test days, liver and muscle glycogen values were assessed before and immediately after a glycogen depleting exercise session on a cycle ergometer. This was followed by a 12-h recovery period where participants remained fasted (CON) or consumed 10 g carbohydrates per kg body mass (BM) in the form of sucrose containing beverages and carbohydrate-rich meals (CHO). Liver and muscle glycogen levels were measured again at 6 and 12 hours into recovery. We applied 13C-Magnetic Resonance Spectroscopy (13C-MRS) to quantify liver and muscle glycogen concentrations and Magnetic Resonance Imaging to measure liver and muscle volume. In addition, muscle biopsies were collected to determine muscle glycogen concentrations. A two-factor (time*treatment) repeated-measures ANOVA was performed, with significant findings being further investigated through Bonferroni post hoc tests. Muscle and liver glycogen data are expressed as percentage signal intensity from 13C-MRS, with pre-exercise values set as 100% with the other values being expressed as relative changes from pre-exercise values. Data are expressed as means ± SD.
RESULTS:
Exercise significantly reduced liver glycogen to 60±12% in CON and 64±16% in CHO, and muscle glycogen to 35±8% of pre-exercise values in both CON and CHO (all P<0.001), with no significant differences between the CON and CHO day (liver: P=0.488 and muscle: P=0.803). Without carbohydrate intake (CON), liver glycogen levels further declined (12 h: 46±11% of pre-exercise values; P=0.002), while muscle glycogen levels remained unchanged (12 h: 38±9% of pre-exercise values) compared to post-exercise values (P=0.596). Following carbohydrate intake (CHO), liver glycogen levels increased beyond pre-exercise values well within 6 h (145±24% of pre-exercise values; P<0.001) with no further increase at 12 h (160±29% of pre-exercise values; P=0.111). Despite ample carbohydrate intake, muscle glycogen levels remained below pre-exercise values after 12 hours of post-exercise recovery (71±12% of pre-exercise values; P<0.001).
CONCLUSION:
Carbohydrate ingestion (1.2 g/kg BM/h) during recovery from exhaustive exercise rapidly replenishes liver glycogen content well within 6 hours. Ingesting 10 g of carbohydrate per kg BM does not fully replenish muscle glycogen stores to pre-exercise values within a 12-hour recovery period.