This post is about something that might be a simple typographical error. Or it might be about spoilers. Or it might be about nothing at all. It is about Shingeki no Kyojin, and although I have read all the manga chapters currently available and seen all the anime episodes that have aired, I will attempt to avoid discussing anything that would be an actual spoiler. Well, unless the above image is itself a spoiler, in which case...oops. I will also discuss all characters in the present tense, but do not assume that has any bearing on whether or not a character lives or dies. Knowing who doesn't die is as much of a spoiler as knowing who does die. Right? [Spoilers: Chiyo lives.] According to this image, Mikasa is 170 cm tall and weighs 68 kg. That seems unusually heavy for an anime character, particularly one of her apparent build. It's not inappropriate for a sufficiently muscular real life girl of her proportions to weigh that much, but from an anime standpoint she's a beast.1 This would not be noteworthy at all if the rest of the characters depicted in that picture had similar builds, but if you accept all those numbers as accurate, Mikasa's fellow soldiers are kinda shrimpy compared to her. Every depicted character who weighs more than Mikasa is both male and at least 5 cm taller.
So, why is that? Well, the simple answer is that Mikasa is a badass. She's the BEST GIRL in Attack on Titan (even though Sasha can tear into a hot potato like none other) and she's probably my current front runner for 2013 Girl of the Year. Being hard core enough to do the things she does, it's sensible that she would be much more muscular than the other characters, even if they're all drawn pretty much the same way in the anime and the manga. The other answer is purely speculation based on something that has already been depicted in the anime but has not been explicitly explained in the first 45 chapters of the manga. For that reason, maybe it counts as spoilers, and maybe it's pure bullshit. I guess it's minor spoilers for people either not watching or a few episodes behind on the anime, and spoilers about what probably won't get explained anytime soon in the anime: In the flashback where young Eren convinces Mikasa to fight, the anime and manga both show a brief "power up" sequence of liquid kickass coursing through her muscles before she attacks, gripping the knife so hard she crushes its hilt and launching herself at her target with such ferocity she shatters a floorboard. Did these things literally happen? Are they unusual events within the in-universe laws of physics? (Which, remember, allow people to Spider-Man their way around town with cans of compressed gas and spring-coiled cables.) We know that childhood bullies were terrified of her and that she's freakishly strong, but does she actually have the ability to Hulk out with superhuman strength that nobody seems willing to question? We know Eren's possibly-up-to-no-good dad visited Mikasa for undefined purposes and has some Important Thing in the basement that everyone's forgotten about after the first episode, but is Mikasa different because she's Just That Good or is she different because of some sort of genetic/magic enhancement? (One that makes her weigh more than her fellow soldiers who seem to have tears and anxiety in the places where Mikasa stores extra beatdowns.)
Note 1: The Body Mass Index calculator for 15-year-old girls at CDC.gov reports Mikasa has a healthy weight.