This study will characterise markers of blood clot risk and systemic inflammation in response to prolonged air travel in highly-trained athletes. Many athletes undertake regular prolonged air travel to engage in training and competition and as such may be subjecting themselves to increased risk of venous thrombosis due to the combined effects of travel, training and injuries (http://www.stoptheclot.org/news/article126.htm). This study will improve sports scientists’ understanding of the level of risk and will assist in developing strategies to prevent adverse events, thus benefiting athlete outcomes and reducing the likelihood of serious injury or fatality in this group.