I would say working out would be the best for you and shoot as much as you can.

I started bow hunting at 15 years old. I started at 35#. I am 45 years old now and hunt at 60#. My advise is to practice practice practice. The strength will come. I would also advise you to hunt at a draw weight that is really easy for you to pull. especially if you hunt in colder weather. It will help you keep movement to a minimum while drawing on a deer and allow you to hold longer if the deer freezes up on you. You will also be more accurate. If you wonder if lower weights kill deer just check out my web site. The proof is there.A well placed arrow beats draw weight every time.
Good luck hunting.

One year on a good working farm will get you in shape real quick.....id suggest some good labor over the summer..

Keep shooting it at those #'s. When I bought my first 60-70# I was younger and had the same problem. At first It was difficult for me to pull back even at 60. I thought I just purchased a bow that was way too much for me!! Couple weeks of practice and I was cranking it up and shooting with ease.

Good Luck

Push-ups, do them every day and increase the amount by 5 every week!

Milk...does a body good!

I would also say that shooting a lot is the best way to build the shooting muscles up. I'm 23 and if I haven't shot in awhile even I start to get a little shaky after about a dozen shots. Besides shooting you should try working out a little bit. You don't even need weights or a gym, I would start just by doing some push ups (some with your hands in tight to your body, others with your hands spread out wider...works different muscles) and some pull ups (really concentrate on using your muscles in your back and not just your arms). In short order that 40 lbs will start to feel like a breeze to pull back.

The best thing I can say is just keep shooting. Work on drawing your bow slowly with proper form...elbow up, it helps you use your back muscles more. You can always draw your bow without shooting in and hold it then let it down. Good luck man, have a blast.

Just keep shooting and you can probably increase just a little at a time. Get plenty of rest, eat plenty of good venison, drink milk, eat home made pasta, do physical work, stay away from the computer, shoot every other day until you are tired andrest.