Christie - I have MS (diagnosed in 2002). It's common for people with neurological issues to have weakness in the signal to the muscles that lift the foot (the foot is really far away from the brain). Also (this is kind of cool), dorsiflexion is one of the last movement patterns we develop, and it's interesting that it's one that is easily lost. I have workshops on neurological disease if you're interested, and there's one here on Pilates Anytime - Neuroscience and Exercise - that you might find helpful.