While the others in the group griped and groaned on a recent Tuesday, Representative Tulsi Gabbard, 34, her Hindu prayer beads wrapped around a wrist for her daily yoga meditation, said little.

"Tulsi, you hearing a lot of whining?" asked Representative Markwayne Mullin, a burly Oklahoma Republican and former professional mixed martial arts fighter who leads the workouts, mocking the complaints of her companions.

"I'm feeling like whining," she replied between push-ups.

Ms. Gabbard, Democrat of Hawaii, has a reputation among her colleagues for being a composed, contemplative presence in a chamber more prone to reaction than reflection.