Muscle metabolism during and after strenuous intermittent running.

Muscle and blood metabolites, plasma insulin and cyclic adenosine 3',5'-monophosphate (cAMP) levels were investigated in five male runners before and after strenuous intermittent running exercise of short duration. Immediately after the exercise, the mean muscle creatine phosphate level (CrP) had fallen by 74% (P less than 0.02) and 30 min later the initial level was regained in only one subject. Other immediate results were increases in mean muscle lactate (460%, P less than 0.005), glucose (130%), glucose-6-phosphate (G6P, 320%) and fructose-1,6-diphosphate (FDP, 32%). Muscle ATP and glycogen concentration had decreased by 31 and 23% (P less than 0.05), respectively. However, ATP, glucose, G6P and FDP changes were not significant owing to the great individual variation. This may have been due to the different training programmes of the runners. Immediately after the exercise mean plasma insulin was 210% (P less than 0.01), blood glucose 71% (P less than 0.005) and plasma cAMP concentration 260% (P less than 0.01) higher than the pre-exercise values. After running urinary excretion of cAMP was 29% higher than before the exercise. It is concluded that exhaustive, short-term exercise activates the liver adenylate cyclase system so giving rise to an increased level of blood glucose, which is an important source of energy during this type of exercise.