Re: I had to (Sob!!) give up my MB.
I think your wanting to get into shape is admirable. What about a compromise? When I first started motorizing bicycles I tinkered around with bike bug motors which were front wheel friction drive and had a whopping 26CCs of squirrel power. Enough to cruise along at modest speed on flats, but not enough for going from a dead stop or climbing hills. With a lever reminiscent of a car floor shift (chrome rod with a round knob on the end) the motor easily engages with the wheel or disengages on the fly. Disengaged there is no contact with the tire, so no drag. Quiet, and unassuming it is a kind of pedal assist and still gives some of the fun of motor bicycling, yet requires some effort on your part, too. Best of both worlds maybe. Just a thought...
Someday when I grow up I will probably lose interest in toys with wheels, but until then...