Endurance athletes, insulin secretion and muscle quality

To study how muscle ubiquinone content (MUQ) and percentage slow twitch (%ST) of muscle fibres in the thighs of male healthy subjects with a low or high insulin response to glucose infusion tests (GIT) affected blood glucose control (BGC).

People with a low insulin response were recruited from sedentary low insulin responders (LIRs) or endurance trained LIRs. A group of men with high insulin response (HIRs) was used for comparison. In addition to GIT, glucose metabolism was estimated with somatostatin-insulin-glucose infusion tests (SIGIT; insulin sensitivity).

Sedentary LIRs and HIRs had low exercise capacities and an increased BGC with increased exercise capacity. BGC in sedentary LIRs, in contrast to HIRs increased with MUQ and/or %ST. Only trained LIRs showed an elevated peripheral insulin receptor sensitivity despite a decreasing MUQ with %ST. This relationship indicated muscle metabolic lesions in trained LIRs with a high %ST and additional compensatory BGC mechanisms in trained LIRs.

BGC in HIRs was maintained with insulin and an exercise-regulated insulin sensitivity, BGC in sedentary LIRs with a good muscle membrane and metabolic control due to adequate MUQ depots, and BGC in trained LIRs with an elevated insulin sensitivity. Trained LIRs rich in %ST had a low MUQ indicative of muscle lesions such as from 'overuse injury'.