I've found I can do 30 minutes on the stationary bike pretty easily any more. Starting out was pretty tough, but it got easier as I kept after it.  I think that's true with just about any exercise.  
  
 I'm with your docs, James.  I know it hurts, but anything you can do, give it a try.  
  
 The gate theory does sound interesting.  I'll google that when I get a minute.  
  
 Dan