well I eat alot and watch alot of tv.
kidding aside exercise is going to help but practice and you need to get the right positions as proper off hand is not about being in olympic condition but about the position.
bone structure does not move or tire like muscles.
here is a exercise that some rifle teams use for off hand.
set your timer for 1 minute and have someone say mount your rifle. what you do is to get your off hand position and fire the shot and then the timer starts for 1 minute you need to keep the rifle in the fireing position. you do that for 22 times in a row and you get a 1 minute break between shots.
cruel but a very effective way to learn a good solid position.
also here is another one that I have used and know that others also use.
you need to be perfectly honest in you shooting as it can be used when dry fireing at home with out ammo.
try to do 10 shots in a row on a target or spot and if any of the shots are not right down the middle you stop and take a couple minute break and think about what went wrong on that one shot and then start over, keep going untill you get 10 in a row thats right.
another one that gets you on the right track is to dry fire with out ammo and do this.
put the sights or scope on the target or spot and pull the trigger and watch the sights after you pull the trigger as they should not move off the center of the target and if they are you are doing something wrong like jerking the trigger or grabbing wood or other things.
its a great exercise for trigger control as are all of the others.
go to the marine or army amu shooting site and look at the off hand positions they fire from and you will get a great ideal on what your position should look like. look at everything in the stance, arm placement, feet position, upper body to lower body placement and so forth.
went out in yesterday and shot some but the wind keep knocking the target off the stand so quit early but before the wind started up real bad I did the dry fire 10 shot thing and after I felt I did it by dry fireing I then did 10 shots in a wind up to 15 mph at my 200 yard sr target with open sights and keep them all in the black with only 2 nines.