Strut-n-Rut has the same thought I had.......you don't need to hold your arm straight out in mid air on the deer(unless of course he's staring a hole thru you! <img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_big.gif border=0 align=middle>)

You can simply hold tight with your back muslces against the wall, and lower your bottom limb until it rests on your thigh......you'd be surprised how long you can hold the bow back without having to hold it UP also.
I drew on a nice buck a few years ago just as his head went behind the only tree on the trail in front of my stand......A big white oak.
I figured it was a slam dunk until he stopped with just his head and shoulders sticking out on my side.
There was a kid playing on a motorbike way up at the top of the field edge, and the buck was locked up watching what that stinkin kid was doing.
I was afraid to let down he was so close, but managed to get the bottom limb resting on my thigh.
I'm not kidding when I say I think I held that bow back for 5-6 minutes......adrenaline helps.
When he finally committed and took 2 more steps the pin was back up and on him with very little movement and it was over........when I released , I realized just how tired my back muslces were, but I NEVER would have gotten that buck trying to hold the bow straight out.
Your back muscles will take much more strain than your much smaller arm muscles, so use them if you have to.