Phosphagens and glycogen content in skeletal muscle after treadmill training in young and old rats

The concentration of creatine phosphate (CrP), ATP, ADP, AMP and glycogen were measured in extensor digitorum longus (EDL) and in quadriceps muscles of 3, 6, 24, and 27 months old male Wistar rats groups. Young (3 months) and old (24 months) rats were trained for 12 weeks, 3 days a week, with running exercise session. Each training session was of 2 h. In sedentary groups and for both muscles, CrP, ATP, ADP, and glycogen contents decrease with aging (between 6 and 27 months). In spite of an AMP increase, total adenosine nucleotides (TAN) decrease significantly between 6-27 months (P less than 0.01) from 6.11 to 5.11 (EDL) and from 5.59 to 4.65 (quadriceps) mumol X g-1 wet weight muscle. After 12 weeks of physical training, the mean values of CrP, TAN, and glycogen were improved in both young and old rat groups. Moreover, the ATP/ADP ratios and the energy charge of the adenylate system were unrelated to age, but training decreases significantly the mean value of energy charge in both young and old groups. These results suggest that, as far as energy-rich phosphagen metabolism is concerned young and old muscles show the same pattern response to training.