Sit in your wheelchair with your feet resting on the floor, and ensure the brakes are applied.
Attach a weight around your lower leg just above your ankle.
Tie a resistance band around your knees under moderate tension.
Position your feet a shoulders width apart against the resistance of the band with your feet flat on the floor.
When ready, lift your foot off the floor by straightening your knee, taking your toes toward the ceiling.
Return your foot to the floor and then repeat.
