there are more than a few good bow holding weight training programs. here's a super simple one where you can use yer current bow as a training tool for holding heavier weights.
with your current, easy to shoot bow, and without using an arrow, draw the bow to your normal anchor, then pull it past that anchor to a predetermined second "anchor" point and maintain proper form.
as an example, if your normal anchor is side-of-mouth, continue drawing to the back of your jaw line. or it could be to your ear.
you should definitely feel this added holding weight tension, but it should not be a strain. it should be effort. there should be no pain.
again, this assumes you have complete control over your current bow - you can draw to full anchor with good form, good line up of your upper body, and hold at full anchor without creeping for at least TWO seconds. if not, you really need to work this training program.
hold the second anchor for a count of 1 or 2 or 3, whatever is easiest for starters. let down.
if yer having an issue holding at your NORMAL anchor, do NOT go to a second anchor, train at your normal anchor first.
do this in increasing reps and hold times, daily.
for the best of shoulder/arm conditioning, hold your bow in your drawing hand (reversed!) and draw it a few times ONLY to your anchor. no weight training for this side of your body, only stretch balance conditioning.
how many training reps? it can vary, you don't want to strain, you want to train. this is important. if something feels like its too much, don't do it. go VERY slow, take it easy, and don't do this if yer not up to it physically or mentally (too tired, sick, stressed out over something, etc). if you do too much, too soon, you will tear down instead of break down and build up. and as we age, we need to slow down, do things easier and for longer periods of time.
for the average person, inside of a month you will be able to easily handle 5 to 8 pounds more holding weight. inside of two months it could be as much as 15 or more pounds of additional holding weight.
this has nothing to do with your physical build or current state of strength. this is a repetitive muscle isometric isolation program and must be done daily or all bets are off. it has helped me (in my advancing years) to continue to hold a 55# bow with very little effort. i know, i know - not a "heavy weight" bow, but for me it means the difference between the 55# i enjoy to having to go down to 45#.
this exercise can also be done with a simple "rubber band" - a bicycle inner tube. so for you white collar desk jockeys, there's no excuse not training to keep in shape with yer current holding weight, or work on holding more weight.