hello, I did a half marathon (13.1 miles) recenlty and I did not carbo load. I finished rather easily.. I had packedtwo snicker bars in my pocket. At the end
of half marathon I had 1 and 1/2 bar left..I did drink some ( a cup or two) powerade & water...

If you just use carb as fuel.. you gonna get lactic acid buildup after some time..(that threshold) fat metabolism does not lead to lactic acid buildup and hence no muscle ache.. my pet theory.. ( hey it is true..)