From what I can gather, this is an extreme case of varicose veins and it's mainly congenital. The condition is caused by faulty valves in the veins of the leg. The valves are supposed to prevent blood from backsliding and collecting in the leg in between heartbeats but in individuals with varicose veins, the valves are stuck open causing blood to collect and the resulting pressure enlarges the veins. The only way that cycling could exacerbate it is because his legs are vertical for long periods at a time during races and so gravity causes the blood to collect in the veins where the faulty valves are located.




