Different metabolic adaptation of heart and skeletal muscles to moderate-intensity treadmill training in the rat

The effect was investigated of treadmill training of moderate intensity on the fatty acid-binding protein (FABP) content in relation to parameters of oxidative and glycolytic metabolism. To this end, the cytoplasmic FABP cont ent and the activity of beta-hydroxyacyl-coenzyme A dehydrogenase (HAD), ci trate synthase (CS), and 6-phosphofructokinase (PFK) were measured in heart , fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscle s (SOL) of male Wistar rats. To investigate the influence of the amount of training (defined as the product of exercise duration, intensity and freque ncy), two training groups were created that differed in training frequency (HF, high frequency 5 days . week(-1), n = 9; LF, low frequency 2 days . we ek(-1), n = 9; the exercise being 20 m . min(-1) for 2 h with no gradient, over 6 weeks) and compared with SC, sedentary controls (n = 7). In heart mu scle, the cytoplasmic FABP content was 34% higher in HF than in SC but was the same as in LF. The CS and HAD activities were no different in the three groups, suggesting that the capacity to oxidize fatty acids (FA) was not a ffected by training. The PFK activity was higher (43%) in HF, suggesting a shift towards carbohydrate utilization. The FABP content and HAD activity d id not change in SOL and EDL after training whereas the CS activity increas ed (27%) in SOL and decreased (21%) in EDL in both training groups. In addi tion, PFK activity in EDL was much higher(113%) in the HF than in SC group. The HF training was associated with a fine-tuning of FA availability and u se in heart muscle, and with a more efficient energy production. It is sugg ested therefore that cytoplasmic FABP could be an early marker of muscle ad aptation to training in heart but not in skeletal muscle. The training rein forced the metabolic profile of the skeletal muscles, in particular that of the fast-twitch glycolytic muscle. We concluded that a large amount of tra ining is needed when the effect on both oxidative and glycolytic parameters is to be studied.