Most members of Congress work out by visiting the House or Senate gymnasiums. But Rep. Howard C. Nielson, R-Utah, got a workout last week when he decided to give his office interns, some tourists and a reporter a special tour of the Capitol dome.

Visitors may walk up the 384 stairs that wind among girders in the airspace between the painted, cast-iron outside of the dome and the iron inside of the rotunda - but only if accompanied by a member of Congress. Nielson, 64, is one of the few who is willing - and in good enough shape - to often lead such expeditions. Construction in the Capitol hadn't allowed such tours for a year and a half - so Nielson had plenty of rest for this trip, and he ended up needing it.The extra work for him started after he led his group from his office in the Longworth Building to a room in the Capitol where he was supposed to meet some tourists. He found the guides had gone to Longworth to meet him.

So he left his group in the Capitol and backtracked the few blocks toward his office. He hurried, in part because a vote was coming up in the House that he didn't want to miss and he wanted to finish the tour before it came.

Once the group was together again, it started winding up the stairs with Nielson stopping often to point out interesting items - such as where the top of the old Capitol dome had been sawed off, or where an artist drew his own face in a tree on a mural and was fired for it.

Halfway up the dome, the inevitable happened. A beeper went off, meaning the vote in House was being taken. Rather than cut the trip short, Nielson left the group with a guide and ran down the dome and over to the House chamber to cast his vote. He then ran back across the Capitol and up the dome to find his party waiting at the very top of the rotunda.

All that running to cast the vote would be the rough equivalent of running up the Washington Monument - or some other skyscraper - just for fun.

Nielson was huffing a bit but was not out of breath, and he quickly launched into an explanation of the surrounding paintings, giving their precise dimensions and whom they depicted, and gave a demonstration of unique acoustics at the rotunda's top.

He then led the group up the final distance in the airspace to just below the statue of Freedom atop the dome. He still had enough breath to explain how in the old days candles were lighted in front of windows there when either House was in session at night so members' spouses would know when to cook dinner.

He then led the group through an outside door and spent several minutes on a windy walkway atop the dome pointing out nearby buildings of interest and their unique architectural characteristics.

Nielson took the group all the way back down the 384 stairs but then decided to take them down several more flights for a personal tour of the Old Senate Chambers, complete with detailed descriptions of how members in the old Senate had to use sand to dry the ink on paper from old quills.

As he walked back toward his office, he revealed his plans for the evening: He was going to play tennis in a doubles match with some of the young college-aged interns a third his age.

Nielson may look a little overweight and a little on the older side, but don't ever get in an endurance race with him - and don't walk with him in the Capitol unless you expect a history lesson no matter what the impediments.