A womans body is not proportioned like mans. Not only is the length of her limbs different, so is the amount of muscle and the distribution of body mass. In fact, anthropomorphic studies show women to have roughly half the upper body strength that men do as a result of our shorter torso, fewer and smaller muscles fibers and additional body fat. What that translates to is a lower ratio of strength to weight and a disadvantage when it comes to comfort and performance - most bikes have top tube lengths that are appropriate for men but require a woman to sustain more force in her shoulders. For a man and woman of the same height, she will be more comfortable on a bicycle with a shorter top tube.