Glycogen resynthesis in liver and muscle after exercise: measurement of the rate of resynthesis by13C magnetic resonance spectroscopy

We have used natural abundance¹³C magnetic resonance spectroscopy (MRS) to measure glycogen content of muscle and liver before and after heavy exercise, and after consumption of different carbohydrate-based drinks. After an overnight fast, five healthy men (mean±SEM age 23±1 years) exercised to exhaustion at 75% of VO_2max on two occasions (mean work rate 165±8 W for 78±14 min) and then, in a single blind random order, consumed either of two drinks containing the same carbohydrate load (177 g). Spectra were recorded over Vastus Lateralis muscle and the liver before and after exercise, and hourly for 5 h after the carbohydrate load. In muscle, glycogen content after exercise was 37% and 31% of basal (preexercise) concentration before consuming the drinks. After carbohydrate loading, glycogen concentration had increased significantly (p<0.05) to 70% and 64% of basal concentration respectively after 5 h. Hepatic glycogen concentration did not change significantly throughout. The study demonstrates the feasibility of sequential MRS measurement of muscle and liver glycogen before and after exercise and after carbohydrate loading.