The effect of acute exercise on glycogen synthesis rate in obese subjects studied by 13C MRS

Abstract

In obesity, insulin-stimulated glucose uptake in skeletal muscle is decreased. We investigated whether the stimulatory effect of acute exercise on glucose uptake and subsequent glycogen synthesis was normal. The study was performed on 18 healthy volunteers, 9 obese (BMI = 32.6 ± 1.2 kg/m(2), mean ± SEM) and 9 lean (BMI = 22.0 ± 0.9 kg/m(2)), matched for age and gender. All participants underwent a euglycemic hyperinsulinemic clamp, showing reduced glucose uptake in the obese group (P = 0.01), during which they performed a short intense local exercise (single-legged toe lifting). Dynamic glucose incorporation into glycogen in the gastrocnemius muscle before and after exercise was assessed by (13)C magnetic resonance spectroscopy combined with infusion of [1-(13)C]glucose. Blood flow was measured to investigate its potential contribution to glucose uptake. Before exercise, glycogen synthesis rate tended to be lower in obese subjects compared with lean (78 ± 14 vs. 132 ± 24 μmol/kg muscle/min; P = 0.07). Exercise induced highly significant rises in glycogen synthesis rates in both groups, but the increase in obese subjects was reduced compared with lean (112 ± 15 vs. 186 ± 27 μmol/kg muscle/min; P = 0.03), although the relative increase was similar (184 ± 35 vs. 202 ± 51%; P = 0.78). After exercise, blood flow increased equally in both groups, without a temporal relationship with the rate of glycogen synthesis. In conclusion, this study shows a stimulatory effect of a short bout of acute exercise on insulin-induced glycogen synthesis rate that is reduced in absolute values but similar in percentages in obese subjects. These results suggest a shared pathway between insulin- and exercise-induced glucose uptake and subsequent glycogen synthesis.

Fig. 1

Euglycemic hyperinsulinemic clamp procedure. Glucose remains constant, while insulin levels increase. Time series of plasma glucose (upper row), glucose infusion rate (middle row) and increase in APE ¹³C glucose in blood due to [1-¹³C]glucose infusion (lower row). Data for lean subjects are indicated by black squares and data for obese subjects by open circles. The dashed vertical line indicates the time at which the exercise was performed

Fig. 2

Typical increase of the ¹³C MR signals of [1-¹³C] glycogen and the α and β anomers of [1-¹³C] glucose during hyperinsulinemia before and after acute exercise in (top) a lean subject and (bottom) an obese subject. Note the steeper signal increase in the spectra of the lean subject

Fig. 3

Glycogen synthesis rates before and after exercise in combination with the exercise-induced increment in lean (black bars, n = 9) and obese subjects (open bars, n = 9). ***P = 0.0001 for lean and P < 0.0001 for obese compared with rates before exercise; ^&& P = 0.004 compared with lean; ^& P = 0.03 compared with lean

Fig. 4

Exercise-induced increments in insulin-stimulated glycogen synthesis as function of whole body glucose uptake; black squares lean, open circles obese. a Individual data and b mean values (±SEM) per group

Fig. 5

Blood flow before and after exercise in lean (top, n = 5) and obese subjects (bottom, n = 3)