I will put my 2 cents in. I have worked for many years in the compound bow industry, first producing/selling and now manufacturing. Here are some simple physics as they apply to compounds, and I would believe to all bows. "You don't get something for nothing," is a simple way to say this, but when a lighter weight bow shoots as fast as a heavier weight bow, it's not magic; the lighter bow is storing as much energy as the heavier one. Energy is stored via the bow being pulled, and you have to pull it. Therefore, you do as much work pulling the lighter bow as you do the heavier bow, although the draw cycle will be (and feel) different. Morrison's bows are known to be on the upper end of fast trad. bows. Is your bow noticeably faster than the other 53lb bows you own, say comparable to a bow in the 56-57lb range? If so, you are doing the same amount of work to store energy with that bow as you are to shoot the heavier bow. Simple physics: energy in, energy out. Delivered energy also depends on bow effieciency, but I doubt the Morrison is decidedly more efficient than your other bows. His bows have a draw cycle that allows them to store more energy, and even if you think it feels the same, or just as smooth, you are doing harder work when you draw it. Hence, your shoulder feels as though you have been shooting a bow 4-6lbs heavier than usual. WHEW! That was way too in-depth, sorry. This is just an observation based on seeing hundreds of prototypes tested in the compound world, and talking to designers who are way smarter than I am. If the bow shoots faster, you have to do more work to pull it, simple. JMHO, Paul.