LIVER GLYCOGEN AND LIVER VOLUME CHANGES WITH EXERCISE

Abstract

The contribution of the liver to glucose provision during exercise is less well studied than that of muscle. Few studies have measured liver glycogen and volume changes as a result of exercise in trained subjects. PURPOSE To measure liver glycogen and liver volume changes as a result of long-lasting exercise. METHODS Six trained males (mean ± SD age 35.8 ± 7.3 yrs, mass 73.5 ± 5.1 kg, VO2max 60.8 ± 6.4 ml·min-1.kg-1) cycled 120 min (one subject 107 min) at 65% VO2max. Standardised evening meal, breakfast and snack (2 hr before testing) were eaten, and no exercise was done 24 h, before testing. Immediately before and after exercise liver volume and glycogen were measured. Glycogen was measured with MRS (Siemens 1.5T). To distinguish liver from muscle, outer volume suppression was used and chemical shift imaging was used to select a voxel of liver tissue of 125 ml. The coil configuration consisted of a 1H coil (15 cm diameter) for decoupling and a 13C surface coil (13 cm diameter) for acquisition. Volume was measured with multi-slice MRI with the 1H coil. Blood samples were taken for glucose and insulin concentration at rest and every 30 min during, and upon completion of, exercise. RESULTS Liver glycogen decreased by 49 ± 30%. Two subjects had extremely low glycogen use (14, 17%). One of these two subjects had higher resting insulin concentration (17 versus range others 6–9 mlU.L-1) and both had higher exercise insulin concentration (mean of 4 samples during exercise: 7 and 8 versus range others 1.8 – 3.3 mIU.L-1). Liver volume (n=5) deceased from 1.74 ± 0.1 to 1.52 ± 0.05 L, i.e. by 12.6 ± 2.4% CONCLUSION Decreases in liver glycogen concentration with 65% VO2max cycling are in line with the limited data published to date with submaximal exercise to exhaustion. An extremely large variation in liver glycogen use was observed. It is probable that non-compliance to the prescribed eating, as indicated by high insulin values and possibly, in one subject, altered glucose regulation and insulin production account for the extreme variability.