I currently stump shoot (ie: jog/run/jump cross-country and take pot-shots at around 85% of full draw weight/length) with self-bows I carve. My average draw weight is 90lbs @ 28.5" full draw, but occasionally I break out my 120lbs @ 28" full draw yew war bows to add some challenge. There's a certain satisfaction in sending an arrow the size of an axe handle at 220'/s across a lake. For non archers, this is like holding a resistance band in each arm and pulling it apart until the resistive force is
X pounds with my two hands
28 inches apart, with one arm using mainly upper back and biceps, and the other using triceps and shoulder muscles.
I'm trying to become comfortable with stump shooting with a 135lbs bow, but seem to have hit a plateau. I personally think the biggest problem is no specialized weight training or plyometrics training methods available. At the advice of forums members from PrimitiveArchery and other archery sites, I've read all four volumes of the Bowyer's Bible, but could only find historical information on the builds (and deformities) of English longbow archers, and nothing about their training regimen.
Are there any resources on training to use well above average draw weight war bows, or training regimens that could aid me? It seems like a very specialized action, so no particular exercises or tools/equipment come to mind.
I've taken care not to over-bulk, am currently at 270lbs @ 13% BF, and have tried various shoulder and back plyometric and powerlifting drills, but they have little impact, while adding extra (un-needed) weight. Any advice is appreciated.