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Did you know that you can change pure fast-twitch fibers ( type IIB) into fast-twitch oxidative fibers (type IIa) by high-volume training such as long duration aerobics or intense high intensity training.

Furthermore, this type of training actually increases the number of mitochondria in fasttwitch fibers to levels higher than those found in slowtwitch fibers. With more mitochondria in muscle cells,the fast-twitch muscle fibers burn more fat. Through
high-volume training your body literally becomes as fat-burning machine. 
 
check out this blog

http://www.muscledog.com/blog/view/208/WEIGHT_TRAINING_EFFECT_ON_FAT_BURNING#

That makes sense, that’s probably why marathon runners look the way they do and sprinters/lifters look the way they do, even after not having done it for very long.

In muscle fibers, fast or slow depends on the motor neuron that is innervating that particular fiber or motor unit.  The number of mitochondria depends on activity level and type.  This applies to both fast and slow.

IMO, and research supports this, the best way to lose weight is not to think about burning fat, but to regularly deplete muscle and liver glycogen via high intensity exercise.