[gwern]

There are studies supporting that, yes, but there is also a study or two which seem to say that the muscle model is a self-fulfilling prophecy! It's a complicated area, let us say. See:

http://lesswrong.com/lw/2y2/willpower_not_a_limited_resource...

http://lesswrong.com/lw/1fe/antiakrasia_technique_structured...

See also

http://lesswrong.com/lw/1fe/antiakrasia_technique_structured...

http://lesswrong.com/lw/1yn/what_would_you_do_if_blood_gluco... (and all the studies in the comments especially)

http://lesswrong.com/lw/h3/superstimuli_and_the_collapse_of_...