I'm not a believer in doing an isolated muscle group while neglecting the remainder of your body. An all around fitness routine that covers the basics in flexibility, endurance, and strength is a better route.
I'm also not a believer in overextending your draw to artificially increase draw weight, I think such practice has a potential to form bad habits and may increase risk for injury. Working towards absolutely mastering your bow weight so that you have complete control at full draw is a better route. Mix up your hold times using your best form at full draw until you reach the point that you can easily dominate your current bow weight. No shaking, no trembling, no I cant hold full draw no more than a second or two. You should be able to easily reach full anchor and hold full anchor for a good duration of time. I've never timed my max hold, but I don't think I'd have any difficulty holding my 67pound longbow 30 to 40 seconds without difficulty. You should completely dominate your current bow weight before going up at all.
At this point, If you wanted to up the weight, the next bow you select add around 5 pounds or so and go at it again. I settled on the 65-70pound range many years ago and have been happy to stay at that weight. I thought about going up a time or two, but have been very pleased at this weight as being ideal for all hunting.
Spend your time gaining complete control over what you have and work your way up slowly over time, and you will be far better off in the long run with better muscle memory and an injury free healthy body.
Tip, a Hill style swing draw where you use a low shoulder and relaxed bow arm elbow will greatly reduce stress and strain on the body.
Best,
DB