Hey Richard, your doing great and hope we both stay at it. If the treadmill inclines, that may help get your heart rate up, I can put it on 6-8% incline and about 4 MPH and my rate hits around 130. Not holding on the handles and the arms swing helps a great deal too. I had knee surgery about 17 years ago and I don't run either. I try to mix it up and do the treadmill, elliptical, stationary bike, rowing machine and stepper. I'm now down 35 pounds since 11/2009 and have found out I have to keep raising the resistance on the cardio and weights. Guess that is what we all are shooting for, being more fit.
Keep us posted on the progress and good luck,