Charisma influences how likable you are not how powerful you appear. Highly charismatic people can draw you into their mindset and thus get you to believe what they want (mostly abstract things). I do not see how it has anything to do with appearances of strength or weakness. Indeed a highly charismatic person can make you like them as they metaphorically stick the knife between your ribs.
in response to: 'Charisma influences how likable you are not how powerful you appear.'
well actually in game it does.
And It takes some charisma to be able to act, and have people truely believe that what you're doing isn't acting. Charisma is also being able to fool people, decieve, etc etc.
Thus by Body language, one could decieve another into believing they have a limp, or fake being injured, and make it believeable, on the other hand they could fake being tough, or stronger then they really are
Some nature examples on earth: Certian Owls will Puff themselves up when they feel threatened! This makes them look bigger, and tougher, so others will leave them alone
However there are rodants and lizards that fake being dead to drive predators away.
Both are examples of using Charisma and body language to decieve others into thinking you're stronger then you really are, or dead, However instead of dead in PS it would be just making yourself look like a wimp.