Glycogen and lactate synthetic pathways in human skeletal muscle in relation to obesity, weight reduction and physical training

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Abstract
The effects of obesity, weight reduction, and physical condition on the concentrations of glucose-6-phosphate (G-6-P) and glycogen, and the activities of glycogen synthase (GS) and lactate dehydrogenase (LD) were determined in resting vastus or gastrocnemius muscles of 40 healthy subjects. In obese women the activity of GS was 50% (P < 0 .cntdot. 05) lower than in lean women with similar levels of glycogen and G-6-P, whereas no difference was found in the activity of LD. Calorie restriction induced a 4 .cntdot. 5% (P < 0 .cntdot.05) decrease in body weight from 82 .cntdot. 5 kg corresponding to a 3 .cntdot. 2% (P < 0 .cntdot.05) decrease in body mass index from 30 .cntdot. 9 kg m-2. The total and fractional activities of glycogen synthase were increased by 50% (P < 0 .cntdot. 05), whereas muscle glycogen content was reduced by 40% (P < 0 .cntdot. 05). The G-6-P concentration and the activity of LD remained unchanged. In well-trained young men the concentrations of G-6-P and glycogen were, respectively, 250% (P < 0 .cntdot. 05) and 50% (P < 0 .cntdot. 05) higher than in non-trained. The fractional and total activities of GS were 90% (P < 0 .cntdot.05) and 50% (P < 0 .cntdot. 05) higher, respectively, and the total activity of LD was only half (P < 0 .cntdot. 05) that of non-trained subjects. In conclusion, physical training enhances the activity of GS, despite a concomitantly increased glycogen content, and thus seems to exert a more efficient stimulus on glycogen synthase than weight reduction. It is indicated that physical training may provide a clinically important contribution to blood glucose reduction in hyperglycaemic conditions.

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