How is Glycogen Supercompensation Regulated in Human Skeletal Muscle

Nine healthy, moderately fit male volunteers participated in the study. The subjects gave written informed consent after having been informed of any possible risk and discomfort associated with the study. The study was approved by the regional ethics committee in Denmark (Journal number: H-4-2013-071) and performed in accordance with the Declarations of Helsinki II. All subjects underwent 3 clinical investigations (day 1, day 2 and day 5) during a 5 day glycogen supercompensation regime. The subjects were asked to refrain from physical activity and to eat a controlled diet containing 60% carbohydrates (CHO) for 4 days prior to the initial experiments. Upon arrival at the laboratory on day 1, the subjects performed one-legged knee extensor exercise for 1 hour at 80% of PWL interspersed by 5 min bouts at 90% of PWL. This was followed by interval exercise until exhaustion containing 4 min bouts starting at 100% PWL followed by 1 min at 50% of PWL. Upon cessation of exercise the subjects showered and rested in the supine position for 4 hours. Then a 120 min hyperinsulinemic euglycemic clamp was initiated by a bolus insulin injection (9.0 mU/kg, Actrapid, Novo Nordisk, Denmark) followed by continuous insulin infusion (1.42 mU/kg/min insulin) reaching a level of plasma insulin around 100 µU/mL (n=9). At least 2 hours before the insulin clamp, catheters were placed in both femoral, one antecubital and one dorsal hand vein. A heat pad was placed around the lower part of the arm and hand in order to "arterialize" blood drawn from the hand vein. Substrate uptake/release across the legs was calculated by multiplying the arterial-venous (AV) difference in blood substrate concentration by femoral arterial blood flow (measured by ultrasound, Philips DICOM). Blood glucose levels were maintained at the euglycemic predefined target by continuously adjusting the glucose infusion rate (GIR) (20% glucose solution; Fresenius Kabi, Sweden). Concurrent measures of substrate AV differenc