[Interconnection of carbohydrate and lipid metabolism in various modes of muscle activity]

The activity of hexokinase and lipase has been determined in skeletal muscles of different metabolic types and adipose tissue of untrained albino rats during two variations of predominant aerobic physical exercise: long-term swimming and long-term swimming including short-term loads (20 s) of maximal intensity (acceleration). Muscle and liver glycogen depletion, serum lactate, glucose and free fatty acids concentrations are also investigated. It is shown that long-term swimming (first variation) has promoted a decrease of both enzymatic activities in muscle fibres and an increase in lipolytic activity of the adipose tissue. During the physical exercise with the acceleration an increase in hexokinase activity occurs in response to 20 min swimming, with its maximal decrease in response to 40 min of exercise. Activity of lipase in slow-twitch oxidative fibres of soleus and in the adipose tissue increases from 20 min to the end of the exercise. Depletion of glycogen in the muscles and liver is determined in fast-twitch oxidative-glycolytic fibres and in the liver in two types of exercises, being more significant in muscles after exercise with accelerations. Concentrations of serum lactate, glucose and free fatty acids remain unchanged after both variations of swimming. So, it may be concluded that acute adaptation to the predominant aerobic physical exercise with activity under short-term loads of maximal intensity has induced a rise of the capacity of oxidative muscles to utilise endogenous and exogenous carbohydrate and lipid reserves.