If someone hasn't lifted weights in several years, would it be a good idea to start with pushups and situps for a few weeks before starting weights. I've had back injuries that put me out for a while and am ready to get back in shape. I have about 30lbs of fat to lose and I'm currently walking/jogging and riding a bike for 1hr 5 times a week. Still working on my diet to get it in check. Any advise will be appreciated.....