Impaired muscle glycogen resynthesis after a marathon is not caused by decreased muscle GLUT-4 content

Abstract

Our purpose was to investigate whether the slow rate of muscle glycogen resynthesis after a competitive marathon is associated with a decrease in the total muscle content of the muscle glucose transporter (GLUT-4). Seven well-trained marathon runners participated in the study, and muscle biopsies were obtained from the lateral head of the gastrocnemius muscle before, immediately after, and 1, 2, and 7 days after the marathon, as were venous blood samples. Muscle GLUT-4 content was unaltered over the experimental period. Muscle glycogen concentration was 758 +/- 53 mmol/kg dry weight before the marathon and decreased to 148 +/- 39 mmol/kg dry weight immediately afterward. Despite a carbohydrate-rich diet (containing at least 7 g carbohydrate.kg body mass-1.day-1), the muscle glycogen concentration remained 30% lower than before-race values 2 days after the race, whereas it had returned to before-race levels 7 days after the race. We conclude that the total GLUT-4 protein content is unaltered in the lateral gastrocnemius after a competitive marathon and that the slow recovery of muscle glycogen after the race apparently involves factors other than changes in the total content of this protein.

Metabolic Consequences of Exercise-Induced Muscle Damage

“…However, a subsequent study by Asp et al (1997) [3] which investigated muscular injury in trained runners following participation in a standard marathon failed to show a decrease in GLUT4 content.…”

“…However, a number of studies have shown muscle glycogen synthesis to be impaired following eccentric exercise resulting in EIMD [2][3][4]6,14,17,18,20] . Some studies have even shown muscle glycogen concentrations to be lower 24-48 hours later compared to immediately after the completion of the exercise bout [48] , suggesting the complete inhibition of glycogen synthesis.…”

“…Type II fibres are predominantly glycolytic and type I fibres are predominantly oxidative [36] , yet both muscle fibre types have been shown to be equally glycogen depleted following predominantly eccentric exercise [2,3,6] , indicating that there is no preferential use of a particular fibre type during eccentric exercise. In a one legged exercise model that required concentric exercise to be performed 2 days after an eccentric exercise bout, Asp et al (1998) [4] demonstrated an increased use of glycogen in the eccentrically damaged leg.…”

“…The symptoms of EIMD are common and easily characterised, and include; stiffness and swelling, decreased force of muscular contraction and delayed onset muscular soreness (DOMS) [1] . In addition, EIMD is often characterised by the presence of the intramuscular enzyme creatine kinase (CK) in the blood [2][3][4][5][6][7][8][9][10][11] .…”

“…These include bench stepping [15] , drop jumps [9,11] and downhill running protocols [8'16] . Other research has examined EIMD following exhaustive exercise containing a large number of SSC contractions, such as marathon running [3,5,10,[17][18][19][20] .…”