feet numbness

Question
I am average runner and a personal trainer and recently quite a few of my clients have ask me just why there feet seem to go numb while they are on the elitical machine, jogging or just running. Do you have any idea why that happens?

Answer
I think part of the reason they go numb on an elliptical is because of the weightless-feel it has.  I imagine it has to do with blood flow going more to the lower extremities and perhaps not getting enough blood flow down to the feet.  I remember in college that there's a vascular 'pump' within our bodies that works with gravity to help pump the blood back 'uphill' in the body.  When gravity is reduced as far as resistance being offered goes, this could affect that 'pump's ability to get blood to return/move properly.  I know I have heard this same kind of thing happening to cyclists with their feet, too, and have only experienced it on really long rides.  I personally don't like elliptical's because of their false sense of getting something done.  I tried working out on Precor's and it could never feel like I could match the same intensity that a run could provide me.

Rick Karboviak