I do not believe its body fat - I believe it is over all body mass and the distribution of it that affects performance - I would expect a 6'2 225 pound weight lifring type with 8% body fat to be much slower than a 6'2 180 pounder with 10% body fat.<br><br>
I like to keep a nice chunk of body fat in my ass to give me a low center of cravity
Apart from being an important fuel source, (distance running) body fat is dead weight.<br><br>
The two examples Flounder gives 8% and 10% are in the athletic range and I would doubt, depending on ability and given the same amount of training that there would be little difference in performance.
Body fat doesn't help you move.. Muscle is helping you move your body forward...<br><br>
I'd expect someone 5'4 140 lb 18% body fat to run better than someone 5'4 140 lb 25% body fat, even given similar training.