More repetitions will help build leaner and defined muscle, but if you want to put on mass you should do less repetitions and more weight. Rest is key.

"After you workout, your body repairs or replaces damaged muscle fibers through a cellular process where it fuses muscle fibers together to form new muscle protein strands or myofibrils. These repaired myofibrils increase in thickness and number to create muscle hypertrophy."

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"Don't be upset by the results you didn't get with the work you didn't do."