I have been involved in weight training for 45 years and I have never met a man or woman who truly had an issue with building muscle mass(bulk) too easily. I have heard of this phenomenon, but have yet to see it.  It requires a manaical effort to acheive excessive muscle hypertrophy. As far as reps go, if you attend any track meet, the person with the higest degree of muscle tone( 100 yard sprinters< 10 secs) , spends the least amount of time at their discipline. If duration(reps) was the key to muscle tone, marathoners would be strung like a bow string. Instead, most of them look like they are suffering from TB. Intensity, not duration, is the key to acheiving muscle tone. Intensity(6-8reps), rest, and nutrition are the three axioms of success. It is difficult for most people to be completely intense for more than 6-8 reps. Many of the health/fitness magazines feature pictures/articles and recommendations of men/women who are manipulating hormones in an effort to acheive a look that by many standards is considered dramatic.

I liked that reply Kaposta.  Really you should just workout and not worry about bulking up or anything because if you ar not intending to bulk up you most likely won't.  It is just to much to really pack on lots of muscle without trying to.  But steady workouts will help you stay toned and in overall better health.