A FIGHTER WOULD HAVE TO BE ALL WET NOT TO LIKE THIS WATER-FILLED BAG

The first real improvement in the heavy bag in 111 years gives a boxer the sensation of having popped someone in the gut. "It feels human," says Tom Critelli of his water-filled invention. "It's 95 percent fluid." In 1872 Simon D. Kehoe patented the bag that's still in general use. It consists of a tube of canvas and leather crammed with sand. After the bag is punched around for a couple of years, the sand tends to settle and lump up; it can get as hard as a column of marble. "I practiced on one as a kid," Critelli says, "and I'd cry every time I hit it." That's why he invented his own.

Critelli is a former Niagara County (N.Y.) deputy sheriff with a black belt in karate who worked out regularly on a conventional bag. Then one day two years ago, he filled a plastic utility bag with water, slugged it and got drenched. But he liked the feel of it. It gave like somebody's belly. So he began experimenting with other materials, and within two weeks he had a working model.

Critelli's Powair Fitness bag is cylindrical like its ancestor, with a vinyl covering and a vulcanized rubber bladder that he guarantees won't burst when you punch it. "For the beating it takes, it's very good," says Donald Hayes, manager of the Times Square Boxing Club in New York, where, among other places, the bag was monitored before being widely offered for sale.

The water bag comes in five sizes, ranging from 55 to 150 pounds. Though slightly more expensive than the sand version (the water bag costs from $92 to $300, compared with about $80 to $290 for sand), the new bag is worth it. Its firmness is adjustable, and it's portable; you can drain it and carry it with you.

Critelli originally tried putting mannequin-like arms onto the bag to make it more lifelike, but the seams kept splitting. Still, he thinks it's the nearest thing to a human body you can hit. It's a lot better than the side of beef Rocky trained on. And it's cheaper than hiring old pugs as sparring partners. Besides, the Powair bag won't sag, crumple or take a dive into the tank.