What happens when there is increased compliance of the vein wall?

Increased compliance of the vein wall allows for a greater volume of blood to be accommodated within the vein at a given pressure. This means that when the vein walls can expand more easily, they can hold more blood and thus may contribute to elevated pressures within the venous system after exercise. When muscles contract during physical activity, they push blood toward the heart, and if the veins are more compliant, they will expand to hold the extra volume being returned. This accommodation can lead to an increase in post-exercise venous pressures, as the increased blood volume does not result in a proportionate decrease in pressure due to the ability of the compliant vein walls to stretch and hold more blood.

In contrast, if vein compliance were lower, you would expect more systemic resistance and potentially lower capacity to accommodate the increased volume from muscular activity, which would not correspond to the situation described in this question.