The First Lady is known to be a fan of working out - never one to shy away from a chance to support her push for a healthier America, Michelle Obama has been spotted playing tennis, running, dancing, even potato sack racing in recent weeks.
So it's perhaps no surprise, then, that she sported a rippling, muscular back at last night's black tie state dinner.
The 48-year-old's dark teal, off-the-shoulder Marchesa gown revealed an impressive set of trapezius muscles - the look topped off with string after string of shimmering blue pearls and beads by Tom Binns.
Admired for her toned and slender arms, the First Lady cut a fine and assured figure alongside Samantha Cameron and their powerful husbands, British Prime Minister David Cameron and President Obama at the star-studded dinner.
But Mrs O has proved she is as comfortable in black tie formality as she is in sneakers and workout kit, and, just weeks ago, threw herself into a gym workout on the Ellen DeGeneres show, pulling a set of exercise moves and challenging the host to a push up a challenge.
Clearly not afraid to walk the walk, she backed up her support of the Let's Move campaign by proving her fitness with an impressive one-armed push up last May, keeping up with the students less than half her age at a DC sports celebration.
Not long after, the fearless Mrs O took on Jimmy Fallon in the White House, inviting the TV host to a tug-of-war contest and even a very unpresidential sack race.
In the past, she had admitted to hitting the gym twice a day in the White House - an occupational hazard that she says stems from the security measures that means she is unable to walk as much as she once did. Her defined arms, legs and now her back have all impressed onlookers.
The hard work is clearly paying off, but not only does Mrs Obama have an enviable body, her sartorial choices of late have won her praise.
An astute choice, the Marchesa gown was designed by Georgina Chapman, who attended the ball and was thrilled to have been chosen to dress the famous fashion maven.
Another designer responsible for dressing both Mrs Obama and Mrs Cameron, London-based Roksanda Ilincic, was clearly impressed: 'First lady Mrs. Obama always looks so chic and modern. I love the addition of texture with the Tom Binns necklace.'