Prior exercise enhances skeletal muscle microvascular blood flow and mitigates microvascular flow impairments induced by a high-glucose mixed meal in healthy young men

Abstract

Key points: Exercise, insulin-infusion and low-glucose mixed-nutrient meal ingestion increases muscle microvascular blood flow which in part facilitates glucose delivery and disposal. In contrast, high-glucose ingestion impairs muscle microvascular blood flow which may contribute to impaired postprandial metabolism. We investigated the effects of prior cycling exercise on postprandial muscle microvascular blood flow responses to a high-glucose mixed-nutrient meal ingested 3 and 24 h post-exercise. Prior exercise enhanced muscle microvascular blood flow and mitigated microvascular impairments induced by a high-glucose mixed meal ingested 3 h post-exercise, and to a lesser extent 24 h post-exercise. High-glucose ingestion 3 h post-exercise leads to greater postprandial blood glucose, non-esterified fatty acids, and fat oxidation, and a delay in the insulin response to the meal compared to control. Effects of acute exercise on muscle microvascular blood flow persist well after the cessation of exercise which may be beneficial for conditions characterized by microvascular and glycaemic dysfunction.

Abstract: Exercise, insulin-infusion and low-glucose mixed-nutrient meal ingestion lead to increased muscle microvascular blood flow (MBF), whereas high-glucose ingestion impairs MBF. We investigated whether prior cycling exercise could enhance postprandial muscle MBF and prevent MBF impairments induced by high-glucose mixed-nutrient meal ingestion. In a randomized cross-over design, eight healthy young men ingested a high-glucose mixed-nutrient meal (1.1 g glucose/kg body weight; 45% carbohydrate, 20% protein and 35% fat) after an overnight fast (no-exercise control) and 3 h and 24 h after moderate-intensity cycling exercise (1 h at 70-75% ${\dot{V}}_{O_2\mathrm{peak}}$ ). Skeletal muscle MBF, measured directly by contrast-enhanced ultrasound, was lower at 60 min and 120 min postprandially compared to baseline in all conditions (P < 0.05), with a greater decrease occurring from 60 min to 120 min in the control (no-exercise) condition only (P < 0.001). Despite this meal-induced decrease, MBF was still markedly higher compared to control in the 3 h post-exercise condition at 0 min (pre-meal; 74%, P = 0.004), 60 min (112%, P = 0.002) and 120 min (223%, P < 0.001), and in the 24 h post-exercise condition at 120 min postprandially (132%, P < 0.001). We also report that in the 3 h post-exercise condition postprandial blood glucose, non-esterified fatty acids (NEFAs), and fat oxidation were substantially elevated, and the insulin response to the meal delayed compared to control. This probably reflects a combination of increased post-exercise exogenous glucose appearance, substrate competition, and NEFA-induced insulin resistance. We conclude that prior cycling exercise elicits long-lasting effects on muscle MBF and partially mitigates MBF impairments induced by high-glucose mixed-nutrient meal ingestion.

Keywords: exercise; glycaemic control; vascular function.