Flying to the marathon

Marathon running has significantly increased in popularity over the past three decades. Running enthusiasts from all corners of the globe submit themselves on a weekly basis to the most arduous bouts of training to prepare for race day. Some are so serious about competing that they may even travel great distances to participate in faraway races.

In a recent study, published in the Clinical Journal of Sports Medicine, researchers from Hartford Hospital examined the effect of air travel on exercise-induced coagulation and fibrinolysis in endurance athletes. The study found that spending all those hours sitting in an aircraft may not be the wisest choice for those who participate in marathon running.

During coagulation, an important part of homoeostasis, the blood becomes more viscous (thicker). The blood forms clots which prevent excessive bleeding in case of a severe wound or cut. In healthy humans, blood clots are constantly formed via the coagulation cascade and broken down to maintain haemostatic balance. While it has been established that endurance exercise activates the coagulatory system, this increase in coagulation is generally paralleled by an activation of fibrinolysis (or clot breakdown).

However, air travel further augments the coagulatory system. Therefore, it is possible that the stress of strenuous endurance exercise, such as marathon running, and prolonged air travel increases the risk of blood-clot formation. Indeed, several documented cases of deep vein thrombosis (DVT, a blood clot in the deep leg veins) and pulmonary embolism (PE, blood clots in the lungs), conditions that are related to pathological clot formation, have been reported in otherwise healthy runners who have travelled via car or aircraft to and from a competition.

Blood needs to travel fluidly through arteries and veins to fulfil basic bodily functions. The circulatory system is compatible with a grouping of multiple interconnected hoses — interconnecting freeways, if you will — that need to be clear to provide for a fluid flow of traffic. A disruption in that flow, for example, caused by a blood clot in the legs, leads to inflammation and swelling, preventing blood from getting back to the heart. In a similar fashion, a clot in the lungs prevents blood from getting the oxygen it needs during breathing.

The small study, led by Dr Beth Parker, examined 41 adults who participated in the 114th Boston Marathon, including one group that flew more than four hours to attend the event and one that lived less than two hours away by car.

The results of the study showed that the combination of air travel and marathon running induces an acute hypercoaguable state.

This haemostatic imbalance was found to be exacerbated with increasing age.

The results of the study have important implications for certain groups of runners. In a phone conversation, Dr Parker explained the major practical applications of her study and research. "Runners with a family history of DVT and PE, those with clotting disorders, older runners and women using oestrogen-based contraception, may want to take certain precautionary steps when travelling to a race," Dr Parker said. "Making sure one does not sit still for a long time, avoiding tight clothes around the thigh that disrupts venous return, staying well hydrated and using tight compression stockings that prevent blood from pooling in the lower extremities are some of the precautionary measures that are advisable."

When I asked her if it would be advisable to extend those precautionary measures to other groups of runners, she was hesitant. Dr Parker noted that such alarm was unwarranted and could actually do more harm than good by actually discouraging active people from accruing the well-established benefits of daily exercise.

For now, just to be extra-cautious, runners could choose to just follow some of Dr Parker's precautionary measures if en route to a faraway race by air, even if these runners don't fall into one of the risk groups. Others may just find all this information a good excuse to stay close to home and just run the neighbourhood marathon.

Ricardo Guerra is an exercise physiologist. He has a Masters of Science in Sports Physiology from the Liverpool John Moores University. He has worked with several clubs and teams in the Middle East and Europe, including the Egyptian and Qatari national teams.