Fat people shouldn't climb stairs for exercise because it can put dangerous stress on their hearts, a physician says.

"Stair climbing is excellent exercise for individuals who are not overweight. However, stair climbing is not the best way for overweight people to lose weight," said Dr. Marque Hunter, a University of Texas Medical Branch pulmonary specialist who tested 20 men at or near their ideal weight and 10 who were 30 percent overweight on a miniature "escalator" sold for exercise."An overweight person must perform an excessive amount of work to climb stairs even at a modest pace," Hunter told the Federation of American Societies for Experimental Biology.

The men were tested at 40, 50, 60 and 70 steps a minute for five minutes at each speed, going without a rest from one speed to the next. Heart rates and oxygen consumption were measured throughout.

Fifty steps a minute is about normal climbing speed, but only three of the fat men managed to get past 40 steps a minute, Hunter said. "Seven of the 10 reached exhaustion in three or four minutes at the lowest speed. The other three reached exhaustion in the next five minutes."

Nearly all of the other group got to 60 or 70 steps a minute for 20 to 25 minutes' exercise, he said.

That kind of activity can cause an extreme rise in heart rate, researchers said. Walking, bicycling or swimming are safer, better and more appropriate exercises.