Physical activity and risk of venous thromboembolism. The Tromsø Study - Borch, Knut Håkon; Hansen-Krone, Ida; Brækkan, Sigrid Kufaas; Mathiesen, Ellisiv B.; Njølstad, Inger; Wilsgaard, Tom; Hansen, John-Bjarne (Haematologica, 2010)