I've found with classes there is some degree of accountability. Last year I took Pulmonary Rehab for my IPD, it was a good start for me. In the early fall, my wife started water aerobics at the local Y (free thru AARP) both going together allowed me to keep up with the needed aerobics. When she paused for knee replacement surgery and follow up PT, the timing didn't work for me (too short of a waiting period from dropping her off to picking her up) and I fell out of the habit. Now we're back to the Y a couple of days a week.