I had two hip replacements a year ago Jan. I am not permitted to do any impatct aerobics. I have a hard time getting my heart rate up on the elliptical and the treadmill. I am still having problems with my flexbility in one leg. The muscles are too tight. Who would ever think that would be a probem; too tight muscles? I would appreciate any suggestions out there on how to improve my cardio indurances.