Changes in concentrations of basic energy-yielding substrates in plasma during maximal effort and postexercise restitution in relation to training level.

Fifty-three cyclists aged from 19 to 32 years were divided into three groups depending on the degree of physical fitness. Group I comprised 13 cyclists with high fitness, group II 19 cyclists with medium physical fitness, and group III 22 cyclists with low physical fitness. All studied subjects carried out work on a Monark cycle ergometer until they refused to go on (exhaustion). During the exercise the consumption of oxygen was determined and the heart rate was measured. Other determinations included the levels of free fatty acids, glucose, amino-acid nitrogen, total protein, lactate in the venous blood and haematocrit index at rest, after the exercise and in the 15th and 30th minutes of postexercise restitution. The differences between the groups were analysed. It was found that in group I the blood glucose level rose more than in the other groups, and the levels of FFA and amino-acid nitrogen increased while in groups II and III they decreased during the exercise. The direction of changes of the various parameters during the restitution was similar in all groups but their intensity was different in individual groups. Lactate concentration showed no differences between the studied groups during the exercise as well as during the restitution.