How does exercise acutely increase glucose uptake by muscles?

• A. Muscle contraction activates AMPK and other pathways that promote GLUT4 translocation to the cell membrane, increasing glucose uptake independent of insulin.
• B. Exercise increases insulin secretion to raise glucose uptake.
• C. Liver glycogenolysis is stimulated to supply glucose to muscles.
• D. Adipose tissue releases insulin-like growth factor to enhance uptake.

Answer: (A)

During exercise, muscles need glucose fast, and they gain it through contraction-activated signaling that moves GLUT4 transporters to the muscle cell surface. When a muscle contracts, energy demand rises, triggering an increase in the AMP/ATP ratio and calcium signaling. These cues activate AMPK and related pathways, which cause GLUT4-containing vesicles to translocate to the plasma membrane. With GLUT4 at the surface, glucose enters the muscle more readily, and this happens even if insulin isn’t driving uptake. This rapid, insulin-independent mechanism lets active muscles quickly fuel glycolysis and maintain performance.

Insulin secretion isn’t the main trigger for this immediate uptake during exercise, and liver glycogenolysis mainly affects glucose availability in the blood rather than directly boosting muscle uptake. IGF-related effects from adipose tissue aren’t the driving factor for acute, contraction-mediated glucose entry into muscle.