A 47-yeаr-оld wоmаn presents with unilаteral calf swelling and tenderness 2 days after returning frоm an international trip. She has no history of trauma or recent surgery and does not take estrogen-containing medications. She reports spending most of the 10-hour flight seated and sleeping without getting up to walk. Which pathophysiologic mechanism most directly contributed to her increased risk for venous thrombosis?