Flingblade is spot on concerning strength training to avoid any shoulder issues. I'm 62 and have been doing some form of strength training on a regular basis since I was 14. I would call most of what I do now endurance strength. I'm of the belief of most shoulder issues for bowhunters being related to an imbalance from just shooting a bow. However, if you will dedicate yourself to strength training, this can be avoided. I have everything from free weights, kettle bells, heavy ropes, various weight sledge hammers (up to 41#), and bands in my garage. There are many ways to skin a cat as they say (really cased is the only way to skin a cat). Very little equipment is required as you can use body weight exercises, sand bags, or firewood for progressive resistance. Just use your imagination.