Question from TOUR reader Jürgen Sch.: I have been cycling road bikes and MTBs for 16 years. After two deep vein thromboses in my calf, which were successfully treated, I am worried about whether I can continue to cycle competitively and take part in cycling marathons. I got one thrombosis after a training break of several weeks and the other after a 14-hour journey. Should I inject heparin before longer journeys in future?
Dr Robert Eifler answers: Your leg vein system is probably damaged by the first thrombosis - despite the treatment that dissolved the blood clot. Anyone who has ever had a deep vein thrombosis, i.e. a clot in the large veins deep inside the leg, has a significantly higher risk of suffering something similar again. During extensive endurance training, the haematocrit value initially falls because the amount of blood plasma - i.e. the liquid component of the blood - increases as an adaptation. After a longer break, the blood becomes more viscous again, as the amount of plasma decreases faster than the number of red blood cells. This increases the risk of thrombosis. For this reason, it is unfortunately not advisable for you to take part in alpine cycling marathons. Intensive road cycling with heavy gears or up steep mountains increases the venous pressure far more than easy pedalling.
Heparin is recommended for longer flights (more than three hours) in conjunction with support stockings. This generally applies to highly trained endurance athletes. The altitude promotes thrombosis. The risk is lower in the car; breaks in the journey with exercise (walking around, gymnastics) have a positive effect here. Low doses of heparin are largely unproblematic in terms of blood clotting in the event of a fall, side effects apart from possible allergic reactions are not to be expected and endurance performance does not change.
