When using 'ankle pumps' or any exercise for lower extremity circulation, use the drinking straw analogy.  If you take rapid, weak sips out of a straw, you don't move much fluid effectively through the straw to your mouth. Likewise, if you perform rapid, weak ankle pumps, you will not move the fluid effectively up the veins toward the heart. Try and move fully in each direction and tense the muscles, holding for a five count. This is a much more effective means of circulation promotion.  It's like taking a slow, deep sip from a straw.