By these numbers, Fesenko had 263 lbs of non-fat body mass (muscle, bone, organs, etc.) in Sept. 2009 but only 253 lbs in Sept. 2010. You basically have him losing 10 pounds of muscle. Something is not adding up.
First and foremost, it's almost impossible to lose fat without losing some muscle as well. Without the assistance of steroids it is impossible.
Looking at these numbers Fes lost 25 lb's total, 10 of which were muscle. That still leaves 15 lbs of fat that he lost as well. That's not a shabby trade off as he now can jump higher & move faster because he has a better muscle to fat ratio. He quite literally has less weight to move around and more muscle ratio wise than before.
Look at it this way. If you take a car that has 500 hp and replace all the metal body cladding with fiberglass reducing the overall weight by 25% and then replace the engine with a 450 hp engine it is going to be faster than the original car even with the smaller engine. There is simply less weight to move. The power to weight ratio has been improved.
Ever wonder why offensive linemen in the NFL are some of the fattest players yet are also some of the strongest players on the field? If you're active it literally takes more muscle to help move that fat around. That's why lard *** linemen can be so strong. Yeah, they are fat asses but they are active fat asses that work out and get exercise. Their bodies quite simply need more muscle to move all that fat around. Now if these same linemen sat around, quit being active and quit working out they would likely lose weight yet their total body fat by weight would stay the same. The weight loss would be due to a loss of muscle mass due to inactivity. Even though they lost weight their body fat % would skyrocket.