Postexercise muscle glycogen synthesis with glucose, galactose, and combined galactose-glucose ingestion

Ingested galactose can enhance postexercise liver glycogen repletion when combined with glucose but effects on muscle glycogen synthesis are unknown. In this double-blind randomized study participants [7 men and 2 women; V̇o_2max: 51.1 (8.7) mL·kg^-1·min^-1] completed three trials of exhaustive cycling exercise followed by a 4-h recovery period, during which carbohydrates were ingested at the rate of 1.2 g·kg^-1·h^-1 comprising glucose (GLU), galactose (GAL) or galactose + glucose (GAL + GLU; 1:2 ratio). The increase in vastus lateralis skeletal-muscle glycogen concentration during recovery was higher with GLU relative to GAL + GLU [contrast: +50 mmol·(kg DM)^-1; 95%CL 10, 89; P = 0.021] and GAL [+46 mmol·(kg DM)^-1; 95%CL 8, 84; P = 0.024] with no difference between GAL + GLU and GAL [-3 mmol·(kg DM)^-1; 95%CL -44, 37; P = 0.843]. Plasma glucose concentration in GLU was not significantly different vs. GAL + GLU (+ 0.41 mmol·L^-1; 95%CL 0.13, 0.94) but was significantly lower than GAL (-0.75 mmol·L^-1; 95%CL -1.34, -0.17) and also lower in GAL vs. GAL + GLU (-1.16 mmol·^-1; 95%CL -1.80, -0.53). Plasma insulin was higher in GLU + GAL and GLU compared with GAL but not different between GLU + GAL and GLU. Plasma galactose concentration was higher in GAL compared with GLU (3.35 mmol·L^-1; 95%CL 3.07, 3.63) and GAL + GLU (3.22 mmol·L^-1; 95%CL 3.54, 2.90) with no difference between GLU + GAL (0.13 mmol·L^-1; 95%CL -0.11, 0.37) and GLU. Compared with galactose or a galactose + glucose blend, glucose feeding was more effective in postexercise muscle glycogen synthesis. Comparable muscle glycogen synthesis was observed with galactose-glucose coingestion and exclusive galactose-only ingestion.NEW & NOTEWORTHY Postexercise galactose-glucose coingestion or exclusive galactose-only ingestion resulted in a lower rate of skeletal-muscle glycogen replenishment compared with exclusive glucose-only ingestion. Comparable muscle glycogen synthesis was observed with galactose-glucose coingestion and exclusive galactose-only ingestion.