With the double-secret-probation-style mystery shrouding the Senate members-only gym, outsiders are left to imagine what happens there, like whether Sen. Jon Tester, D-Mont., uses the treadmill.

This is precisely what HOH asked the No. 2 Senate Democrat, Majority Whip Richard J. Durbin of Illinois, in a wide-ranging sit-down interview about the gym.

“You know, I’ve seen him on the StairMaster, the rowing machine. Jon really pours his heart into it. He really goes at it hard,” Durbin said.

As part of a stakeout of the gym last week, keeping close track of which senators arrived and left and when, Tester’s appearance before 7 a.m. was one of the most surprising sights.

There’s something about the Paul Bunyan-esque myth of Tester — a myth propagated by his crew cut, seven fingers, generous use of profanity and proficiency with a tractor — that makes it tough to imagine him being a gym rat, as opposed to just waking up, walking to the fridge and downing a dozen raw eggs.

Perhaps Tester also bench-presses some of his colleagues, say, Alabama Republican Jeff Sessions? “You could see him doing that,” Durbin mulls, letting out a smile. “He’s a pretty big fella.”