If lack of time is stopping you from exercising then doing a 20 second all out sprint just three times a week has been shown to reduce your risk of diabetes and increase aerobic fitness.  Try this… three times per week, walk at a moderate pace for 9 minutes, then sprint for 20 seconds as fast as you possibly can.  If you have back, joint, knee problems or just hate running, use a bike instead. If you haven’t exercised for a while get a quick check up with the doc before starting.