Someone"s been hitting the gym again! The First Lady"s designer gown reveals her ever-so-toned back muscles

Someone's been hitting the gym again! The First Lady's designer gown reveals her ever-so-toned back muscles

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UPDATED:

14:02 GMT, 16 March 2012

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.

Worth the weights: Michelle Obama, ever a fan of working out, sported a very toned back at last night's black tie state dinner

Worth the weights: Michelle Obama, ever a fan of working out, sported a very toned back at last night's black tie state dinner

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.

Blue belles: Samantha Cameron, left, could have flaunted some decolletage at the tuxedo event but instead chose to cover up

Blue belles: Samantha Cameron, left, could have flaunted some decolletage at the tuxedo event but instead chose to cover up

Fine figure: Mrs Obama's arms have always garnered praise, but last night it was her back that looked finely honed after hours in the gym

Tone it up: Arms as slim and well-defined as ever, the First Lady looked graceful, assured and statuesque in her Marchesa gown

Tone it up: Arms as slim and well-defined as ever, the First Lady looked graceful, assured and statuesque in her Marchesa gown

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.

Ever-competitive: The First Lady takes on Ellen DeGeneres on her TV show, demonstrating her strong back muscles as she easily completed a set of push-ups

Ever-competitive: The First Lady takes on Ellen DeGeneres on her TV show, demonstrating her strong back muscles as she easily completed a set of push-ups

Keep movin': Mrs Obama dropped down and gave us ten in May 2011 as part of her Let's Move initiative

Keep movin': Mrs Obama dropped down and gave us ten in May 2011 as part of her Let's Move initiative

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.'