Q I am an airline pilot and spend about 80 hours a month on flights from six to 10 hours long. I have heard you should avoid training after flying for a time equivalent to the time you’ve spent airborne. Is this true? Am I at risk from blood clots?
A At the cabin altitude of 7,000ft blood chemistry gradually changes with pro-clotting factors going up and anti-clotting factors going down. Fluids tend to accumulate in the lower legs. As long as you remain immobile, your risk of forming clots in the lower legs increases steadily. Sudden swelling of one leg would indicate a clot, but sometimes clots move on before they cause swelling. A moving clot is called an embolism. If it lodges in a lung it can cause pain or death. Unfortunately, there is no way to know you have an embolism until it manifests itself in pain or death.
A surprisingly large amount of cases of clotting involve athletes – particularly endurance athletes. Rather than avoiding training too soon after a flight, you need to pay attention to preventing clots forming during flight: frequently flex the lower legs, wear compression stockings and drink isotonic drinks (one cup per hour). These are explained at www.airhealth.org .
If an unstable clot is forming, waiting a few hours before training would probably not make any difference. In most cases, no symptoms of clots are noticed until several days after the flight. Exercising immediately might keep a clot from growing larger but this by itself would not be a good reason to exercise vigorously soon after air travel; it’s more important to pay attention to avoiding clots.
—Mike Reynolds, Executive Director, www.airhealth.org