We already have a system about correlation of general fatigue (breathing) and sight Swaying. With this tandem we get an interesting management of human powers, and accordingly even more interesting infantry combat simulator.
This fatigue is not forcing us to rest indefinitely, but only makes the spending power right at the right time.
This will work good with weapon resting(if it's added), and without it.
Usefull links.
http://www.ncbi.nlm.nih.gov/pubmed/12834134
http://digitalscholarship.unlv.edu/thesesdissertations/1038/
http://en.wikipedia.org/wiki/Recoil_operation