actually using heavy weight stimulates the fast twitch which is the the whiite fibers.. usually meant for building the nervous system to be able to handle controled heavy lifting.. these fibers consist of type a & type b fast twitch fibers ... and the red fiber are the slow twitch were these fiber and handle long resistance and they dont fatigue easy,, the way fast twitch fibers do.. these are endurance fibers usually for hypertrophy & conditioning training.. (for separation & tie-ins of muscle).. these are at a pace of 8 to 25 reps per set..

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