A few years ago, I was working as a juvenile probation officer and the county got a hair-brained idea to send all the PO's through the police academy. At the time I wasn't working out at all. I had three weeks notice, so I immediately started walking. 10 minutes a day for 3 or so days, lots of stretching before and after. Then increased it to 15 or 20 minutes w/ more stretching. Then I went up to 30 minutes per day and even more stretching. Then I'd walk for 10 minutes, jog for 5, then walk the rest of the half hour. I slowly replaced the walking w/ jogging and then a fast run, so that I was walking the first and last five minutes. We started running the first day in the academy and I did fine, while some of my co-workers and the LEOs in the academy got shin-splints or pulled muscles,etc. We worked up to doing 5-7 mile runs, nothing outrages, but I dropped my 1.5 mile time from 18 m to 12 m in the course of a month. Not bad for a guy who's broken both ankles, dislocated a knee cap and has arthritis in the knee.
I did other core exercises as well, pushups, situps (I hate situps), leg lifts, crunches, curls, squats, etc.
I've lost 38 lbs since January b/c I was sore every morning when I woke up and got winded after two flights of stairs. Neither one of these happen no and all I've done is lost the weight. Cardio is next.