The longbow was made of a single piece of yew wood, with the heartwood forming the inside of the bow and the sap wood facing out. The heartwood resisted compression and the sapwood provided elasticity. I think that's how it goes...
They found an intact longbow preserved in a cold deep river some years ago. They were “surprised” at how heavy the pull was. For some reason they never said what it actually was. Some bow hunters present when I read the article guessed 200lbs. I’d bet higher given the way they practiced. It’d be nice to know.