
While there is no scientific evidence that lifting an amount of weight sufficient to fatigue your muscles by 8-repetitions will cause you to “bulk up”, anecdotal information suggests this may be true for a few individuals. For the majority of women, lifting this amount strengthens and tones muscles and actually causes them to drop a dress size or two.
However, there are some individuals (like yourself) who may build muscle more easily than others. If you prefer to lift a slightly lighter amount of weight - one which you can lift 12-15 times in good form before needing a rest - that is fine. You will still strength your muscles and bones, and enjoy the slimming effects of lifting weights regularly.