What happens to insulin levels during exercise, and how does this affect glucose uptake?

• A. Insulin increases; this reduces glucose uptake
• B. Insulin decreases while exercise stimulates muscle glucose uptake
• C. Insulin remains constant; glucose uptake stops
• D. Insulin becomes inactive; glucose uptake is unchanged

Answer: (B)

During exercise, working muscles need more glucose, and they can take it up even when insulin levels are not high. Muscle contraction itself triggers a pathway that moves GLUT4 glucose transporters to the muscle cell membrane, increasing glucose uptake independently of insulin. At the same time, plasma insulin tends to fall or stay low because of the body’s hormonal response to exercise. The combination means glucose uptake by active muscle rises despite lower insulin.

That’s why this option is the best: insulin decreases, yet muscle glucose uptake is stimulated by the contraction signal. The other ideas—insulin increasing, glucose uptake stopping, or uptake being unchanged—don’t fit because contraction-driven GLUT4 translocation boosts uptake even without insulin and insulin levels typically don’t rise during exercise.