At a Boston fundraiser Wednesday, Sen. Elizabeth Warren, D-Mass., joked about how First Lady Michelle Obama's well-toned arms show she has a tough fighting spirit.

"I love Michelle Obama. She's a real fighter. Just take a look at those biceps," Warren said to laughter and applause at a Democratic Senatorial Campaign Committee fundraiser at the Taj Boston Hotel on Wednesday.

One day after President Obama officially endorsed Rep. Ed Markey in the Massachusetts Senate race, Mrs. Obama headlined the fundraiser benefiting the Democratic Senate candidate's campaign against Republican candidate Gabriel Gomez. A Markey aide said the fundraiser raised at least $600,000.

"My husband can't do it alone," Mrs. Obama said. "He absolutely needs folks like Ed Markey in the Senate to make it happen. So here in the state of Massachusetts, we need you do everything you can over these next four weeks to get Ed Markey elected."

While in Boston, the first lady was scheduled to meet with survivors of the Boston Marathon bombing whom she visited in the hospital last month. In the evening, Mrs. Obama will attend two DNC fundraisers in New York City, including a DNC LGBT gala featuring Jason Collins, the first openly gay active player in the NBA.