You know, I really like this idea! It is a perfect cover story! This needs to be the plot for a side villain, because I would so read it!
It is part of the job to flaunt the body, but it also has an element of classiness and prestige as a traditional dance art which gives it respectability in most parts of the world. Unless you are just
[Redacted]. No offense
[Redacted] and
[Redacted]. You know, I had a rather offensive joke here that goes a
wee bit too far into the personal roasting, so Imma just remove that
. I was channeling my inner Moxie's opera opinions too much...
And I'll contrast what
@SailusGebel said, because he's wrong, obviously not understanding the capabilities of a ballerina. Despite their - on average - light weight class (and one can keep in mind, this could be an especially tall ballerina who was chosen to stand out amidst the rest of the ballet troupe), they regularly perform feats of strength on levels outmatching other sports. The amount of force required to support themselves on the tips of their toes is frankly absurd, and the kicks they do day in and day out, giving them a considerable advantage when it comes targeting blows that can cause serious bruising and bone shattering, potentially even internal hemorrhaging for particularly good blows. They also require considerable grip strength to perform feats of agility, which makes strangling people (according to the California Courts, only 11 pounds of force applied on both carotid arteries for 10 seconds to induce unconsciousness, only FOUR POUNDS on the jugular for 10 seconds to induce unconsciousness, and 33 pounds to crush the trachea. And one shouldn't underestimate the originality that applying their teachings should allow them for using their impressively developed muscle strength in their legs and core strength to absolutely demolish your average joe (particularly in a surprise ambush with a bait of some variation to obtain isolation and privacy for their dirty deeds, as most serial killers do).
And on top of the more traditional strengths of the ballerina, SailusGebel is unaware of the fact that modern ballerinas are including a LOT more weightlifting and traditional exercises. Crosstraining using other sports is not uncommon. According to The Guardian, one ballerina is cited as repping 220 pounds. You get tricked, buddy, and you could get knocked flat easy with the right leverage, leaving you brain damage and or brain death to boot to boot. On average, they can do twice their weight, easy. That matters quite a bit, regardless of whether you are a heavy wuss or not.
AND! On top of that, you are ignoring the small, noticeable, effect that exercising one part of the body, despite not touching another, will still increase that part's muscle by a bit (New York Times). So on top of the huge amounts of work they already do on the upper body, if you still want to focus on more traditional upper body strength, they will be getting those returns from their even greater amounts of exercise on the lower body.