Foot pumps are rehabilitation exercises to prevent vein clots when the lower limb is likely to be immobilised for a period of time.
Forcibly rocking the foot from the ankle activates the muscle pump in the calf.
As the calf muscles contract and compress the vein, the blood can only move in one direction - back to the heart.
The muscle pump in the calf
The veins of the lower limbs rely on a series of valves to help move the blood back to the heart. As the calf muscles contract, the blood - unable to go back down because of the valves - moves up back to the heart. This keeps the circulation going, and helps to prevent blood clots in the calf (deep vein thrombosis).
Foot pumps without graduated compression stockings for prevention of deep-vein thrombosis in total joint replacement: efficacy, safety and patient compliance Pitto RP and Young S. Int Orthop. 2008 Jun; 32(3): 331–336.