Glucose uptake is increased in trained vs. untrained muscle during heavy exercise.
Endurance training increases muscle content of glucose transporter proteins (GLUT-4) but decreases glucose utilization during exercise at a given absolute submaximal intensity. We hypothesized that glucose uptake might be higher in trained vs. untrained muscle during heavy exercise in the glycogen-depleted state. Eight untrained subjects endurance trained one thigh for 3 wk using a knee-extensor ergometer. The subjects then performed two-legged glycogen-depleting exercise and consumed a carbohydrate-free meal thereafter to keep muscle glycogen concentration low. The next morning, subjects performed dynamic knee extensions with both thighs simultaneously at 60, 80, and until exhaustion at 100% of each thigh's peak workload. Glucose uptake was similar in both thighs during exercise at 60% of thigh peak workload. At the end of 80 and at 100% of peak workload, glucose uptake was on average 33 and 22% higher, respectively, in trained compared with untrained muscle (P < 0.05). Training increased the muscle content of GLUT-4 by 66% (P < 0. 05). At exhaustion, glucose extraction correlated significantly (r = 0.61) with total muscle GLUT-4 protein. Thus, when working at a high load with low glycogen concentrations, muscle glucose uptake is significantly higher in trained than in untrained muscle. This may be due to the higher GLUT-4 protein concentration in trained muscle.
Kristiansen
S
S
Department of Human Physiology, Copenhagen Muscle Research Centre, University of Copenhagen, DK-2100 Copenhagen, Denmark.
Gade
J
J
Wojtaszewski
J F
JF
Kiens
B
B
Richter
E A
EA
D000222:Adaptation, Physiological; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007866:Leg; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology*; D012016:Reference Values; D013848:Thigh
D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; D006003:Glycogen; D005947:Glucose