Michelle Obama Has a New Workout for 50: More Yoga, Less Cardio

We all know about the bicep curls behind her famous Michelle Obama Arms.

Now, as the First Lady turns 50 this week, throw in a downward dog for good measure.

In her only interview on the occasion of her milestone birthday Jan. 17, Mrs. Obama tells PEOPLE she's tweaked her workout routine with an eye toward her 70s and 80s.

"I'm seeing myself shift from weight-bearing stuff – even though that continues to be important – and the heavy cardio and running, to things like yoga that will keep me flexible," says Mrs. Obama, who will be feted Saturday at a dance party hosted by President Obama at the White House.