How Veins Work - Normal Veins and Valves

When normal veins undergo "pumping" by movement of the muscles in the legs, the veins get squashed. This results in the blood getting forced upwards into the pelvis.

However, when the muscles relax and the veins open again, the blood would rush back into the leg (called reflux) if it weren't for the valves stopping this from happening.

The prevention of this reflux by the valves is the key to how veins protect the legs in normal people. When the valves are working the vein is said to be "competent".