Without getting too nerdy and going too deep into the physiology of the deal... the cells in your muscles store a bit of fuel for instant use. It takes about a minute for that fuel to be replaced. So, if you're not taking a full minute between the release of one arrow till drawing the next, you're running your muscles out of fuel and making them get fatigued.

That's especially true if you're putting your muscles under a great load, at the upper end of their capability. If 70 pounds is all you can draw, then those muscle cells are using up nearly all their fuel each shot. If you're shooting more than an arrow a minute, you're not giving them time to 'recharge' and it's not going to take long before the fuel is completely depleted.You feel fatigue set in.

That's as far as I'm going with that. I've done my best to forget everything I learned in those 16 hours of anatomy and physiology classes, and recalling even that much has given me a headache.If you want to be nerdy andknow more about the basics of it, this is a fairly decent article: http://www.bodybuilding.com/fun/drobson24.htm

If you don't want to know more, can't say I blame you.

Anyway, bottom line is,if you want to shoot more then reduce your draw weight and wait a minute between each arrow. Then you should be able to shoot for hours.

For target shooters (and I'm talking about the NFAA paper punchers who shoot 4 arrows per target and 112 arrows per round, not thewimply 3D guys who can't shoot more than one arrow per target and 30-40 arrows a day is 'challenging'[8D]) it's not uncommon for their target bows todraw at least 10 pounds lighter than their hunting bows.