Elmer,
Going up 30-40#'s in draw weight is a challenge, and how you progress depends a lot on your age, physical condition and athletic aptitude.Do it right, and you will be happy.
If you are young and athletic you may be able to go up comfortably, and shoot the heavy bow very well in 3-6 months. If you are over 45 it may take a year.
Now, most people will find they can build the strength to shoot the heavier bow, even 30-40#'s heavier, much faster than that. That is not the problem. Injuries are the problem.
They come to the tendons and suppoting muscles which develop much more slowly than the big muscles you would think make for pulling heavier bows. And,they can ruin your day, week, season, year.
Avoiding injuries requires careful progress:
1. Always warm up before shooting a heavy bow. Not just by shooting a lighter bow, Do some pushup, pull-ups, shrugs, rowing, or cable exercises. Warm up - or else.
2. Regular workouts for the back and shoulders to build the supporting muscles. Shooting the bow is not enough.
3. Go slow. As soon as you think, "this is easy" and push it - you'll be sorry!
4. Stop when you develop any soreness, and let it rest a few days. Ice packs.
Injuries typically appear in the tendons and supporting muscles. The older you are the more likely you are to force an injury by pushing too fast, too heavy, too much repitition. Tendonitis can appear in the draw hand fingers and bowarm elbow. Muscle strains (even tears) can happen in the shoulder rotator cuff muslces and tendons of both arms, especially the bow arm if you do not line up with good form.
Back off at soreness as these do not get better with more exercise. You have let it heal then start back lower and go slower. If you get one of those "pops' that hurts like the dickens later in the day or next day, you are out for weeks. These injuries can force you to stop shooting at all for 2-3 months to heal - a real set-back for an avid archer. Go slow to go fast, or you can spend a year working through injuries. Ice packs help soreness and real injuries require a total layoff for 2-3 months.
Allen is right, practice with the lighter bow especially to warm up. Then limit your work on the heavier bow to a few shots, and do not shoot it every day. Slowly build up. Byron Ferguson shoots 73#'s and says he has to limit practice to every other day now.
Also the back and shoulder excercises help to develop the suppoting muscles which shooting the bow does not. Shooting the bow builds the muscles that are pushing and pulling the bow. The supporting muscles in the rotator cuff just sit there until one day, you are not lined up in good form, under heavy boww strain and "pop" a supprting muscle is sudenly called into action way over its limit.That's bad. Do excercises to build the shoulders and rotator cuff muscles. Don't go for the olympics here, or you can injure these little muscles in over-done workouts.
I was 54 when I jumped from a 50# recurve to a 70# longbow. Wow! The bow was not so hard to build up to, and I shot it every day, after two moths hitting a tennis ball regularly. Yep, got all of the above injuries, and finally one day I shifted my bow arm under strain, and "Pop" - had to lay off completely for 3 months to let the bow-arm rotator cuff heal. Could not even shoot the 50# bow to stay sharp.
After that I built up slowly and did regular, slowly increasing, weight training.
When i started back I ran into soreness, and found if I always warm up before I shoot a heavy bow in practice, that does not happen. Hunting is not so hard on you, as you may only shoot one or two arrows.
Today, I'm 56, and just got my 85# Howard Hill Wesley Special. It's a dream to shoot, and smoothly accurate. I can shoot it easily, but I warm up, and limit my number of arrows as I grow into it. This is the danger zone, as the strain/injury potential at 85# is greater than ever.
Two years from 50# to 85#, but we have to see if I can avoid injuries in this territory.
Good shooting!