Vacuum Pump
I hafta admit I was skeptical until I got mine done. It takes a 'firm foot' alright, to lock 'em all up on dry land, but not at all what I'd call excessive. And like I said, my legs are not all that strong, anymore.
I can't walk far, can't be on my feet long, and break out the 'lectric wheelchair for air / car shows or fairs.