ENDURANCE TRAINING FAILS TO INHIBIT SKELETAL-MUSCLE GLUCOSE-UPTAKE DURING EXERCISE

The effects of endurance training (running 30 m/min, 10% grade for 90 min, 5 days/wk for 12 wk) on skeletal muscle glucose uptake during ste ady-state exercise (running 20 m/min) were studied in fed rats. A bolu s injection of 2-[1,2-H-3]deoxyglucose was administered to assess the glucose metabolic index (R'g), an indicator of glucose uptake, in indi vidual tissues of animal. After 55 min of rest or moderate exercise, v arious tissues were analyzed for accumulation of phosphorylated 2-[1,2 -H-3]-deoxyglucose and/or glycogen content. No differences were observ ed between groups in the resting glycogen content for any of the muscl e samples examined. Resting plasma glucose concentrations were not sig nificantly different between groups. Furthermore, no significant diffe rences were observed in R'g between groups for any of the muscles exam ined (tibialis anterior, extensor digitorum longus, soleus, white gast rocnemius, red gastrocnemius). During exercise, plasma glucose concent rations were not significantly different between groups. Exercise sign ificantly elevated R'g above resting values in the tibialis anterior ( 5-fold), soleus (3-fold), and red gastrocnemius (7.5-fold). Despite an elevated R'g for specific muscles during exercise, no significant dif ferences were observed in glucose uptake between groups for any tissue examined. Concomitantly, trained animals exhibited significantly less muscle glycogen depletion during exercise compared with control anima ls. Liver glycogen levels were also significantly higher post-exercise in trained vs. control animals. Despite an apparent attenuation of gl ycogenolysis, endurance training does not inhibit skeletal muscle gluc ose uptake during moderate exercise.