Effects of glucose ingestion on blood flow in the small intestine and exercising limbs during endurance exercise.

Performance during endurance exercise depends on the balance between the blood flow (BF) to active muscles and their energy use. We compared the acute cardiovascular regulation after the ingestion of a 300-mL drink containing 50 g glucose (G trial) or not (water, W trial) during the ninth minute of 40 min of bilateral knee extension exercise in 12 healthy participants. The blood pressure, heart rate, cardiac output, gas exchange variables, and BF through the superior mesenteric (SMA), femoral (FA), and brachial (BA) arteries and skin in the forearm and chest were measured continuously. Regional vascular conductance (VC) was calculated as BF/mean arterial pressure. BFFA significantly decreased after glucose ingestion, but did not change after water ingestion. BFSMA significantly increased from 15 min after glucose ingestion to the end of protocol, but did not change after water ingestion. BF through the BA and forearm and chest skin during the G and W trials significantly increased after drink ingestion and did not significantly differ between the trials. Temporal changes in the VC of the FA, SMA, BA, and skin of the forearm and chest mirrored the BF responses in each vessel. The central hemodynamic variables, V̇o2, and V̇co2 responses did not significantly differ between the G and W trials. These findings imply that the cardiovascular responses to glucose ingestion during exercise involve the redistribution of some of the BF in the active limbs to the small intestine for digestion and absorption, but no additional increase in cardiac output.NEW & NOTEWORTHY This study is the first to comprehensively assess regional blood flow (BF) responses to glucose ingestion during exercise. We demonstrate that glucose intake during high-intensity exercise increases intestinal BF, while reducing the flow to active limbs, without changes in cardiac output. These findings imply that there is a competition between digestion and working limbs for limited circulatory resources, and provide novel insight into how carbohydrate intake affects BF distribution and energy delivery during endurance exercise.