The major mechanism promoting venous return by the contracting muscles squeezing the veins as they change shape is:

• A. Pocket Valves
• B. Respiratory Pump
• C. Venous Pressure
• D. Skeletal Muscle Pump

Answer: (D)

The main idea is that when skeletal muscles contract they act as a pump for the veins. As muscles shorten and bulge, they squeeze the veins embedded between them, raising the pressure inside the veins. The one-way valves in these veins ensure blood is pushed toward the heart and cannot flow backward. This skeletal muscle pump is a key driver of venous return, especially during activity when muscles are actively contracting. The respiratory pump and venous valves play supporting roles, but the description of contracting muscles squeezing veins to change their shape and move blood toward the heart points to the skeletal muscle pump.