Carbohydrate metabolism during hard exercise and in the recovery period after exercise

The glycogenolytic rates during maximum exercise with different durations have been calculated using own studies and reports from the literature. The initial glycogenolytic rates both in animal and in human muscle are close to the Vmax as determined in vitro. Already within the first seconds of electrical stimulation of human muscle the glycogenolytic rate reaches the maximum value and the phosphorylase is transformed to the a form to near 100%. Continued electrical stimulation or dynamic exercise for longer periods than 30 s results in successively decreasing rates of glycogenolysis, and a reversion back of phosphorylase a to b. The mechanism for this reversion is not known. In a study by Hermansen and Vaage from 1977, it was suggested that lactate formed during exercise could be resynthesized to glycogen by gluconeogenesis in muscle during the rest period after exercise. This study was repeated in our laboratory with addition of measurements of oxygen uptake and splanchnic metabolism. The results showed that only 10% of the lactate formed was taken up by the liver and that maximally 40% was oxidized during an 1 h recovery period. About 7% of the formed lactate remained unchanged in the body at the end of the recovery period. This leaves more than 40% of the lactate unaccounted for. Analysis of muscle tissue showed that glycogen content in muscle had decreased by 41 mmol glucosyl units X kg-1 after exercise and that 50% of this carbohydrate was retained in muscle as free glucose, phosphorylated intermediates and lactate.(ABSTRACT TRUNCATED AT 250 WORDS)