How to: Workout to get lean rather then bulk
Whenever I train with people, especially women, I get the comment “I do not want to bulk up. I just want to tone.” I usually go into a quick explanation as to why that should not be a concern. They should be more concerned about not lifting intense enough to get the significant results they are after or simply known as “toning.”
Although, this generalization is not going to apply to every women I train. You’"ll see the occasional woman at the gym with definition that rivals any man, or even the blatantly buff physique of any Ms. Universe contestant. Extraordinary muscle hypertrophy, or muscle growth achieved by these women, are not results from typical training routines.
Three factors predict muscle growth: relationship of resistance and reps or intensity, distribution of fast and slow-twitch fibers in the trained muscle, and the individuals’ level of testosterone. Increasing muscle mass requires a definitive amount of overload on the trained muscle group anywhere from six to 12 repetitions. Completing fifteen reps or more before fatigue sets in does not result in significant growth of the muscle. While low reps (three to five) with high intensity leads to more neurological adaptations.
Also, fast-twitch, apposed to slow-twitch, fibers are more influential in actual muscle growth. The first two factors in muscle growth (intensity and fiber type) are still dependent on testosterone levels produced by an individual and determines muscle building capability. Testosterone is the difference in muscle building potential between males and females.
So the moral of the story, lift big or go home.
Source; American Council on Exercise