I don't believe being in shape or not, caffiene intake, or the phase of the moon has anything too do with good offhand shooting. There is only one way to be good at it, it's called "practice", and lot's of it. Get a good .22 and shoot 50 or a hundred rounds a day. Can't get outdoors? How about an air rifle? There are no shortcuts here. Going to a gym might make you feel good, but without constant target practice, it won't help offhand shooting one bit.