During the working session the test subjects will be exercising for 2 hours on a bicycle ergometer at 65-75% of VO2-max. Afterwards these two hours of bicycling exercise, the persons will be performing a number of one minute intervals at maximum workload. Every interval will be followed by a one minute break, where the subjects pedal at low intensity of own choice. This interval exercise will be continued until the test subject's plasma glucose is below 3.89 mmol/l. This value is selected to ensure that the glycogen storage in the liver is depleted to identical extent in each test.