I haven't been here in months, so busy, but I hope my response helps you!
I don't know if we're talking about the same thing, but I find when I'm doing cardio, whether it's aerobics or stationary bike, elliptical, whatever, my feet get pins and needles and go numb.
I went to a podiatrist earlier this year and mentioned it to her and she said it's a common problem.
There is a growth of tissue that commonly occurs between the bones in the foot, kind of in the middle. Something to do with the metatarsal (sp?) region. That's what's affecting the feeling in my feet anyway. She said it starts as a small problem, but gets worse with age, causing more pain and inconvenience. She gave me a small adhesive pad which sits in my work shoes, pressing on the area between the ball of my feet, and the arch. It helps to spread the bones of the feet out so they don't rub together and inflame the lump.
Sounds gross, but might be something to think about. Hope I've helped