well ... because my question is about how i've known some girls with legs that are much more muscular than than mine but not as strong ... hence the question about muscular size vs. strength
I want more muscular legs ... not really stronger legs (although as a by-product I really wouldn't mind that)
Makes me wonder if I should be doing lunges and aerobics like a lot of these girls rather than squats which they rarely do ?
Well, the pic of the girl you showed looks in competition condition, so any time you have someone whose bodyfat is lower they appear more muscular ... but the short answer is, yes, a person can have larger muscles and not have the same level of strength. Strength and hypertrophy are, in a strange way, almost two different animals.
Also, there's a lot that goes into making a muscle appear large. I mentioned bodyfat, but you also need to consider height and frame size. I'll use myself as an example. If I flex my upper arm right after working out I can probably get over 16" but big deal
I'm a long limbed 5'9" it really doesn't look like much. Put that same 16" upper arm on mesomorphic girl who stands 5'3" and it's a whole different ball of wax.
Going back to your original post, you are interested in what is called HYPERTROPHY. A program like a 5 x 5 is geared more towards overall strength development, it's a solid core program, and certainly a great starting point. But I'm sorry, there is no magic number (pulling or pushing a certain amount of weight) that will give you a certain muscular look. How your muscles develop is entirely dependent on what type of muscle fiber you've got in any given body part. Being able to squat 225 may not necessarily give your legs the look you want, neither may squatting 550. Legs are notoriously difficult to get to bulk up for a lot of people (for which there is a perfectly good evolutionary reason, legs are generally made up of slow twitch fibers which are better for endurance). Slow twitch muscles are more efficient at using oxygen to generate more fuel (known as ATP) for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch fibers and can go for a long time before they fatigue. Therefore, slow twitch fibers are great at helping athletes run marathons and bicycle for hours.
Fast twitch fibers use anaerobic metabolism to create fuel, they are much better at generating short bursts of strength or speed than slow muscles. However, they fatigue more quickly. Fast twitch fibers generally produce the same amount of force per contraction as slow muscles, but they get their name because they are able to fire more rapidly. Having more fast twitch fibers can be an asset to a power lifter or body builder, since they need to quickly generate a lot of force.
As a general rule of thumb, slow twitch muscles have a longer appearance and don't bulk and bunch in the same way as fast twitch muscles (think of it this way, Lance Armstrong would probably NEVER make a good bodybuilder).
I mean, I'm by no means an expert, but just trying to give you a starting point.
And in the final analysis, even if you're considering stepping on a stage someday, weight training is about competing against yourself. Setting
your goals, achieving them, and surpassing them. Comparing your abilities or appearance against another person a formula for permanent disappointment. There is
always someone out there (of either gender), who is bigger, stronger or more cut than you will ever be. On the other hand, there truly are no limits to the potential your own body has, how much you can do or how far you can take yourself.
Please Scroll Down to See Forums Below 
