Which factor below does NOT assist venous return of blood?

C: While contraction of smooth muscle can decrease the volume of veins and so shift more blood to the arterial side (and increase blood pressure), This is not the same as assisting the continuous return of blood to the right atrium. Breathing (the respiratory pump) assists the return of blood from the abdomen; skeletal muscle contraction (and valves) assist return from the limbs; and gravity assists return from the head.