Which factor primarily propels blood toward the heart during the calf muscle pump?

• A. Arterial pulsations
• B. Gravity
• C. Lymphatic pumping
• D. Contracting leg muscles

Answer: (D)

Calf muscle contraction acting as a pump is the main driver of venous return from the leg. When the calf muscles contract, they compress the deep leg veins, raising intraluminal pressure and pushing blood upward through the one-way venous valves. The valves prevent backflow, so the blood moves toward the heart with each squeeze. When the muscles relax, the valves stay closed to stop retrograde flow, and the cycle repeats with the next contraction. Gravity can influence blood flow depending on position, but without muscle contraction the return is slow and pooling can occur. Arterial pulsations affect arteries, not the venous return in this context. Lymphatic pumping moves lymph, not blood, so it doesn’t propel venous blood back to the heart.