I've had to let up on more than one occasion. Buck walks behind tree, I draw, buck stops behind tree, I hold at full draw, buck stays behind tree, I begin to shake violently and sweat profusely, buck still behind tree, I have to let up. This has happened a couple of times. Sometimes you just can't do anything about it. I like the trick davidmil talked about. If one of these situations ever happens again, and I'm sure it will, I'll have to give it a try. Oh yea, I've never timed how long I can hold at full draw but it's probably not much over a minute.