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Using a heavier bow to train with has been a practice technique for a long time. I recently read a very old treatise on archery from China which indicated that once an archer learned how to shoot well using a “light-drawing bow” they needed to train to be able to draw much heavier draw weights. Please note that their example of a light-drawing bow was one of roughly 60 pounds of draw. The heavier bows were 80 pounds and higher.
So, advantages of modern technology have changed things and the requirements of target archery have changed them again.
Ordinary archers in ancient historical (means “for which we have written records”) times were in essence artillerymen. These archers lobbed relatively heavy arrows into masses of men and animals in the expectation that they would hit something because there were so many “targets” all clumped together. The actual “marksman” was quite rare. The accounts of extreme marksmanship usually came from martial arts schools (which can be trusted to always tell the truth, right?).
So, to address the question of training using a heavier bow.
This is not a regular thing. This is done to increase stamina or to build strength to support a heavier bow during regular shooting. The vast majority of your practice should be at the draw weight you compete in. This is because archery is a “feel” sport and the “feels” of the two bows are quite different.
Consider the example of a baseball player in the “on deck” circle preparing to bat during a game. They often use a heavier bat or add weights to their own bats which gets their muscles warmed up and makes their regular bat feel light in their hands. But before they approach the plate, they swing their normal bat several times, often trying to synchronize their swings with the pitcher’s pitches. Imagine what would happen if the batter took a heavier bat into batting practice and batted with nothing but it. When the game rolled around he would find his timing destroyed and he would be unable to hit at all.
The occasional use of a higher drawing bow to develop stamina and strength is advisable. So, you might do ten minutes of reversals with the heavier bow (always focused on having proper form) every other practice or during a fitness program supporting your archery. Something like that. You could go on a more extensive regimen to prepare for a draw weight increase (which are limited to 2# at a time for recurve archers so as to not destroy the form already learned). The draw weight should be something you can handle but noticeably heavier than you are used to, e.g. 5-10#.
The reason we draw such lighter weights today is that for target archery, we are shooting very small targets (and one designated beforehand), we are shooting a great many more arrows, and our arrows are considerably lighter than those of antiquity, plus our bows are more consistent. All of these factors favor shooting with a lower draw weight over a higher one.