Y'know, pointing out the use of specifically the ankle to move the pedal brings up something similar to using your arm or your wrist or your fingers when playing with a drum stick. Generally, the larger the muscle group the more potential for volume there is, but there's less potential for speed as well. It's an inverse relationship between the two attributes, so as you get faster, you could say that you start with perhaps your hip or your knee, then your ankle, and then I guess you're using your toes! Although that sounds silly, it would be a good idea to look into using different joints and muscle groups and types of movement in your playing, OP. Bass pedal technique is pretty difficult to pin down because of how little real hard research there is on it.