The time of ingestion of a carbohydrate supplement on muscle glycogen storage postexercise was examined. Twelve male cyclists exercised continuously for 70 min on a cycle ergometer at 68% VO2max, interrupted by six 2-min intervals at 88% VO2max, on two separate occasions. A 25% carbohydrate solution (2 g/kg body wt) was ingested immediately postexercise (P-EX) or 2 h postexercise (2P-EX). Muscle biopsies were taken from the vastus lateralis at 0, 2, and 4 h postexercise. Blood samples were obtained from an antecubital vein before and during exercise and at specific times after exercise. Muscle glycogen immediately postexercise was not significantly different for the P-EX and 2P-EX treatments. During the first 2 h postexercise, the rate of muscle glycogen storage was 7.7 mumol.g wet wt-1.h-1 for the P-EX treatment, but only 2.5 mumol.g wet wt-1.h-1 for the 2P-EX treatment. During the second 2 h of recovery, the rate of glycogen storage slowed to 4.3 mumol.g wet wt-1.h-1 during treatment P-EX but increased to 4.1 mumol.g wet wt-1.h-1 during treatment 2P-EX. This rate, however, was still 45% slower (P less than 0.05) than that for the P-EX treatment during the first 2 h of recovery. This slower rate of glycogen storage occurred despite significantly elevated plasma glucose and insulin levels. The results suggest that delaying the ingestion of a carbohydrate supplement post-exercise will result in a reduced rate of muscle glycogen storage.

The purposes of this study were to determine whether the muscle insulin resistance of the obese rat is due to a defect in the glucose transport process and whether the insulin resistance is fiber-type specific. The hindlimbs of fasted, 14-wk-old obese (fa/fa) and lean (fa/?) Zucker rats were perfused with perfusate containing 8 mM glucose and no insulin or 8 mM glucose and either a physiological (0.15 mU/ml), a submaximal (1.50 mU/ml), or a maximal (15.0 mU/ml) insulin concentration. Glucose uptake was determined after which the initial rate of glucose transport was determined using 3-O-methyl-D-glucose (3-OMG). Glucose uptake of the obese rats was depressed by 40, 33, 42, and 47% in the absence of insulin and in the presence of the physiological, submaximal, and maximal insulin concentrations, respectively, when compared with lean littermates. Glucose transport in the absence and in the presence of the three insulin concentrations was significantly lower in the soleus (slow-twitch, oxidative fibers), red quadriceps (fast-twitch, oxidative, glycolytic fibers), and gastrocnemius (mixed fibers) of the obese rats when compared with lean rats. Glucose transport in the white quadriceps (fast-twitch, glycolytic fibers) was significantly lower in the obese rats in the absence of insulin and in the presence of the submaximal and maximal insulin concentrations. The glycogen concentration and the activity of hexokinase were the same and the glycogen synthase activity was higher in the muscles for the obese rats when compared to lean rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Two treatments that increase skeletal muscle insulin action are exercise training and high-carbohydrate diet. The purpose of the present study was to determine whether exercise training and a diet high in carbohydrates could function synergistically to reduce the muscle insulin resistance in the obese Zucker rat. Obese rats 4 wk of age were randomly assigned to an exercise or sedentary group. Each group was subdivided by diet with one-half of the rats fed a high-carbohydrate diet and one-half fed a high-fat diet. Lean Zucker rats fed the high-fat diet were used as controls. Muscle insulin resistance was assessed during hindlimb perfusion with a submaximally stimulating concentration of insulin. Exercise training and the high-carbohydrate diet increased the rate of muscle glucose uptake in the obese rat by 46 and 53%, respectively. More importantly, the combined effect of exercise training and high-carbohydrate diet was greater than the sum of their individual effects. Glycogen synthesis paralleled glucose uptake and was the major pathway for intracellular glucose disposal. Muscle glucose uptake for exercise-trained, high-carbohydrate fed obese rats was comparable with that of lean controls. It is concluded that exercise training and the high-carbohydrate diet functioned synergistically to reduce the muscle insulin resistance in the obese rat.

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