Threshold foot drop.
Do you see it in this gait? No. There is a clue though, the EHL on the right (extensor hallucis longus) does not seem to be all that hearty and robust during gait, the toe is not as extended/dorsiflexes as on the left foot. A Clue ? Yes.
This client had true blatant foot drop, but it was caught relatively immediately, and the source resolved and recovery ensued. There is still some residual weakness, as you see at the end of the video, but making steady gains. Previously, gait showed obvious foot drop, foot slap, abrupt knee flexion (the "catch" response as we call it as the client's knee suddenly flexed forward as foot slap occurs). But, as you can see , the gait is pretty much normal now except for a little EHL strength lag. But, at the end of the video, when they heel walk, one can see the weakness, they cannot keep the ball of the foot off the ground during attempted heel walk. We like to call this "threshold weakness", it is just hovering below the surface, when taxed, it can be seen, but doesn't show up in gait. But, it does show up in longer endurance based walking events. This may be when your client's symptoms show up, as fatigue expresses limitations in the system. It just goes to show you, if you are not testing and looking for these things, you just might not find the source of your clients knee pain, foot pain, hip or low back pain. Heel and toe walking takes 10 seconds, do not forget to check them off. It just might be the "big reveal" for you, and them !
-Shawn and Ivo, the gait guys