A seat exercise device for use onboard a mobile platform such as a commercial aircraft is disclosed, wherein a passenger engages the exercise device while seated to reduce the risk of deep vein thrombosis (DVT) during extended periods of travel. The preferred embodiment of the present invention comprises a leg support secured to a passenger seat and a foot support secured to a lower end of the leg support. A trombone spring is secured between the leg support and the foot support such that a passenger may push down on the foot support to flex and contract thigh muscles. Additionally, a pivot spring is secured between the leg support and the foot support such that a passenger may pivot the foot support to flex and contract calf muscles. Accordingly, the flexing and contracting of leg muscles increases blood circulation and reduces the risk of DVT during long flights.